回應1
pele159:
1. 請問 HCl(aq) & HCl(g)係咪compound ?
2. 地球最多的 element 係咪 oxygen ??地球最多的 metal咪 Iron ??
3. conc.H2SO4 + heat 係咪react cu ?Iron heat conc.H2SO4 係會出咩呀 ??
4. 係咪只有HNO3 stored in brown bottles ?
5. 其實而家應該做出面練習的mock 定係 redo 錯嘅野,溫下書好呀 ??
化學友:
1. HCl係covalent compound， (aq)同埋(g)只係代表唔同嘅states。
2. 地球最多嘅 element 係oxygen(之前寫錯,多謝網友指正)。地球最多嘅 metal係 aluminium。
3. Cu + 2H2SO4 --> CuSO4 + SO2 + 2H2O
Iron heat conc.H2SO4:
Fe + 2H2SO4 --> FeSO4 + SO2 + 2H2O
4. 除咗HNO3, 仲有AgNO3同埋KMnO4。CE chem大約知咁多就得o架喇
5. 化學友覺得你應該redo錯嘅野喇，同埋溫番dnote，唔好剩係做題目，會更有效。
回應2
pele159:
1. 86 Q.2The melting points of diamond, sodium chloride and potassium increase in the order:
A. diamond, sodium chloride, potassium
B. potassium, sodium chloride, diamond
C. sodium chloride, diamond, potassium
D. sodium chloride, potassium, diamond
請問 Metallic bond 和 ionic bond , 邊果melting points 大 d 呀 ?
2. 86 Q.38Bromine exists in two isotopic forms, 3579Br and 3581Br . The relative atomic mass of bromine is79.9. Which of the following statements is/are correct?
(1) The relative abundance of each isotopic form is about the same.
(2) The two isotopes have different numbers of protons.
(3) The two isotopes have different numbers of neutrons.
A. (2) only
B. (3) only
C. (1) and (2) only
D. (1) and (3) only
請問(1)點解arm 呀 ?
3. 87 Q.32(1) Nitrogen does not react readily with other elements or compounds.
(2) The outermost electron shell of the nitrogen atom is completely filled.
點解(1) 係arm 呀 ?? 乜Nitrogen 唔係covalent bond ?? 如果要does not react readily with other , 乜唔係 Noble gas 果d咩 ??
化學友:
1. 一般o黎講ionic bond強過metallic bond。所以ionic compound 嘅melting point 係高過metal。
2. 其實當年marking係錯o架。因為79Br有55%而81Br有45%，所以relative abundance is not about the same。
3. nitrogen(N2)內有nitrogen-nitrogen triple bond。化學反應時，需要好高energy才可以break nitrogen-nitrogen triple bond，所以佢係好少reaction，好unreactive。但係佢都有reaction嘅，例如: 3Mg + N2 à Mg3N2。
當然noble gases比N2 unreactive得多啦。
回應3
carmenlee:
你好，我有個chem既問題想問下OCl-會turn red litmus paper blue then white啦;咁H2SO3 turn完blue litmus paper red之後會唔會turn white?p.s.我見d solution都冇寫佢會turn white，但係SO3 2-唔係都bleach到野架咩?
化學友:
carmenlee，你係correct o架。但係SO32-嘅bleaching power比較mild，要long time先可以turn litmus paper white，所以ans只係寫即時observation。
回應4
sinying:
我想問下呢:alkonal加Na,CH3COOH加Na係唔係會都出H2??我睇書話佢地都係會出OH- ion,所以有H2放但咩唔係只係H+ion加Na先會出H2咩?OH-加Na為何出H2,而且CH3COOH唔係ACID來的嗎?咩唔係會出H+...........THX
化學友:
係呀，佢地會出H2 o架:
2CH3CH2OH + 2Na --> 2CH3CH2ONa + H2
2CH3COOH + 2Na --> 2CH3COONa + H2
sinying，化學友唸你睇錯o野喇。凡親一隻compound有H+或者hydroxyl group(-OH group 唔係OH- ion)就可以同Na react to give H2 o架啦。CH3CH2OH有 -OH group而CH3COOH有H+，所以有reaction。
2007年4月29日 星期日
會考化學(12)
係第五章Redox(氧化還原)裡面，同學仔記住要留意以下幾點:
1. 連接兩個half-cells(半電池)之間所用嘅salt bridge(鹽橋)，目的嘅係容許half-cells內嘅ions(離子)互相通過。 睇睇下面嘅pastpaer:
1995 Paper I 9b
2004 Paper II 40
2006 Paper II 40
2. 好多時卷二都有條計氧化數同埋判斷邊條係氧化還原反應嘅mc，e兩年好多考生都錯，所以要小心。睇睇下面嘅pastpaer:
2005 Paper II 8
2006 Paper II 3
2006 Paper II 27
3. 如果我地想acidify potassium permanganate(酸化高錳酸鉀)或者係sodium dichromate(重鉻酸鈉) 所用嘅acid應該係dil. sulphuric acid (硫酸)。唔用HCl(aq)(氫氯酸) 嘅原因係MnO4-會oxidize(氧化)Cl-(氯離子)。 唔用HNO3(aq)(硝酸)嘅原因係HNO3自已都係1隻oxidizing agent(氧化劑)，佢嘅存在會同MnO4-或Cr2O72-爭住oxidize另一隻reducing agent，出現unexpected result。睇睇下面嘅pastpaer:
1999 Paper II 15
4. 比較Fe2+同埋Fe3+嘅difference:
Fe2+
colour: pale green(淺綠色)
+ NaOH: dirty green precipitate
+acidified KMnO4: pale green --> yellow
Fe3+
colour: yellow(黃色)
+NaOH: brown precipitate
+acidified KMnO4: no observable change
5. 解釋reaction係唔係redox, 只需寫出reducing agent(還原劑) 或者係oxidizing agent (氧化劑) 嘅 change of oxidation number (氧化數轉變)。例如，2Na + Cl2 --> 2NaCl係redox，因為嘅O.N. of Na increases from 0 to +1 / O.N. of Cl decreases from 0 to -1。
6. 注意在electroplating(電鍍)裡，anode(陽極)、cathode(陰極)和electrolyte(電解質)嘅配搭。睇睇下面嘅pastpaer:
1993 Paper I 2a
1995 Paper II 11
1996 Paper I 9b
係第六章重要嘅工業產品裡面，同學仔要留意以下幾點:
1. Chlorine(氯氣)溶係NaOH係一個redox reaction(氧化還原反應)，而最重要係Cl同一時間 oxidized同埋reduced。
Cl2 + 2NaOH --> NaCl + NaOCl + H2O
Cl嘅O.N.changes from 0 to -1(Cl2--> NaCl)
at the same time Cl嘅O.N. changes from 0 to +1(Cl2 --> NaOCl)
睇睇下面嘅pastpaer:
1997 Paper II 21
1999 年 Paper II 36
2. compare chlorite ion(次氯酸根離子)同埋sulphite ion(亞硫酸根離子)作為bleachingagent(漂白劑)嘅分別:
睇睇下面嘅pastpaer:
1998 Paper II 32
2001 Paper I 9d
2005 Paper II 17
3. Conc. sulphuric acid(濃硫酸)同dilute sulphuric acid(稀硫酸)不同嘅特性。只有conc. sulphuric acid有 oxidzing property同埋dehydrating property，而di. sulphuric acid就冇。
Oxidizing(氧化性) of conc. sulphuric acid:
Cu + 2H2SO4 --> CuSO4 + SO2 + H2O
C + 2H2SO4 --> CO2 + SO2 + 2H2O
S + 2H2SO4 --> 3SO2 + 2H2O
Dehydrating(脫水性) of conc. sulphuric acid:
CuSO4.5H2O --> CuSO4 + 5H2O
C12H22O11 --> 12C + 11H2O
(C6H10O5)n --> 6nC + 5nH2O
4. conc. sulphuric acid同埋dil. sulphuric acid都有嘅相同特性。
同alkali solution(鹼溶液) react:
H2SO4 + 2NaOH -->Na2SO4 + 2H2O
同carbonate salt(碳酸鹽)嘅反應:
H2SO4 + Na2CO3 --> Na2SO4 + CO2 + H2O
1999 Paper II 7
2001 Paper I 9c
5. o向計算molar volume(摩爾體積)時，要留意以下兩點
i. 在same no. of moles(相同的摩爾)下，gas嘅體積比liquid同埋solid大好多，所以記住一mole N2同一moleNaCl或者一moleH2O嘅volume係唔同。睇睇下面嘅pastpaer:
1998 Paper II 46
2000 Paper II 48
ii. 留意計diatomic gas molecule(雙原子氣體分子)時，係問atom(原子) 定係問molecule(分子)，d考生成日都wrong o架。睇睇下面嘅pastpaer:
2001 Paper II 27
1. 連接兩個half-cells(半電池)之間所用嘅salt bridge(鹽橋)，目的嘅係容許half-cells內嘅ions(離子)互相通過。 睇睇下面嘅pastpaer:
1995 Paper I 9b
2004 Paper II 40
2006 Paper II 40
2. 好多時卷二都有條計氧化數同埋判斷邊條係氧化還原反應嘅mc，e兩年好多考生都錯，所以要小心。睇睇下面嘅pastpaer:
2005 Paper II 8
2006 Paper II 3
2006 Paper II 27
3. 如果我地想acidify potassium permanganate(酸化高錳酸鉀)或者係sodium dichromate(重鉻酸鈉) 所用嘅acid應該係dil. sulphuric acid (硫酸)。唔用HCl(aq)(氫氯酸) 嘅原因係MnO4-會oxidize(氧化)Cl-(氯離子)。 唔用HNO3(aq)(硝酸)嘅原因係HNO3自已都係1隻oxidizing agent(氧化劑)，佢嘅存在會同MnO4-或Cr2O72-爭住oxidize另一隻reducing agent，出現unexpected result。睇睇下面嘅pastpaer:
1999 Paper II 15
4. 比較Fe2+同埋Fe3+嘅difference:
Fe2+
colour: pale green(淺綠色)
+ NaOH: dirty green precipitate
+acidified KMnO4: pale green --> yellow
Fe3+
colour: yellow(黃色)
+NaOH: brown precipitate
+acidified KMnO4: no observable change
5. 解釋reaction係唔係redox, 只需寫出reducing agent(還原劑) 或者係oxidizing agent (氧化劑) 嘅 change of oxidation number (氧化數轉變)。例如，2Na + Cl2 --> 2NaCl係redox，因為嘅O.N. of Na increases from 0 to +1 / O.N. of Cl decreases from 0 to -1。
6. 注意在electroplating(電鍍)裡，anode(陽極)、cathode(陰極)和electrolyte(電解質)嘅配搭。睇睇下面嘅pastpaer:
1993 Paper I 2a
1995 Paper II 11
1996 Paper I 9b
係第六章重要嘅工業產品裡面，同學仔要留意以下幾點:
1. Chlorine(氯氣)溶係NaOH係一個redox reaction(氧化還原反應)，而最重要係Cl同一時間 oxidized同埋reduced。
Cl2 + 2NaOH --> NaCl + NaOCl + H2O
Cl嘅O.N.changes from 0 to -1(Cl2--> NaCl)
at the same time Cl嘅O.N. changes from 0 to +1(Cl2 --> NaOCl)
睇睇下面嘅pastpaer:
1997 Paper II 21
1999 年 Paper II 36
2. compare chlorite ion(次氯酸根離子)同埋sulphite ion(亞硫酸根離子)作為bleachingagent(漂白劑)嘅分別:
睇睇下面嘅pastpaer:
1998 Paper II 32
2001 Paper I 9d
2005 Paper II 17
3. Conc. sulphuric acid(濃硫酸)同dilute sulphuric acid(稀硫酸)不同嘅特性。只有conc. sulphuric acid有 oxidzing property同埋dehydrating property，而di. sulphuric acid就冇。
Oxidizing(氧化性) of conc. sulphuric acid:
Cu + 2H2SO4 --> CuSO4 + SO2 + H2O
C + 2H2SO4 --> CO2 + SO2 + 2H2O
S + 2H2SO4 --> 3SO2 + 2H2O
Dehydrating(脫水性) of conc. sulphuric acid:
CuSO4.5H2O --> CuSO4 + 5H2O
C12H22O11 --> 12C + 11H2O
(C6H10O5)n --> 6nC + 5nH2O
4. conc. sulphuric acid同埋dil. sulphuric acid都有嘅相同特性。
同alkali solution(鹼溶液) react:
H2SO4 + 2NaOH -->Na2SO4 + 2H2O
同carbonate salt(碳酸鹽)嘅反應:
H2SO4 + Na2CO3 --> Na2SO4 + CO2 + H2O
睇睇下面嘅pastpaer:
1998 Paper I 8a1999 Paper II 7
2001 Paper I 9c
5. o向計算molar volume(摩爾體積)時，要留意以下兩點
i. 在same no. of moles(相同的摩爾)下，gas嘅體積比liquid同埋solid大好多，所以記住一mole N2同一moleNaCl或者一moleH2O嘅volume係唔同。睇睇下面嘅pastpaer:
1998 Paper II 46
2000 Paper II 48
ii. 留意計diatomic gas molecule(雙原子氣體分子)時，係問atom(原子) 定係問molecule(分子)，d考生成日都wrong o架。睇睇下面嘅pastpaer:
2001 Paper II 27
回應(會考化學)
回應1
正式嘅解釋化學友都唔敢肯定，大致係指alcohol可以溶解blood裡頭嘅fat，令到blood嘅viscosity降低(即係令d blood冇咁黏)。如果dblood黏，可能會引至血管閉塞，咁就會有heart attack。
Sinying:
1. 我想問下呢~detergent 的hydrolysis.係唔係有得用H2SO4用NaOH架??兩種有D咩分別??
唔該哂
2.係sacrificial potection 裏,如Zn用來protect Fe,我想問Zn會唔會oxidize 同oxygen 會唔會form around Zn??
3.ZnO + hydroxide ion係會出d咩? ZnO又唔會溶水,有冇REACTION,仲會唔會redissolve架??
超級thanks
化學友:
1. 唔係o架。只有NaOH + fat/oil先會做成soap，H2SO4係唔得o架。你可以睇o下下面化學友回應pele159嘅回應丫。化學友比多兩條equations你睇，可能會更易明:
2. Sacrificial protection 係用Zn 代替 Fe loss electrons變成Zn2+，而oxygen and water react形成OH-，Zn2+會同OH-react生成zinc hydroxide around zinc。
3. e條有少少out c o架。ZnO同Zn(OH)2一樣會redissolve in excess OH-生成Zn(OH)42-
Maryuen:
我想知道關於alcohol的什麼是thinning of blood?
它跟being less rpone to heart attack有什麼關係??
正式嘅解釋化學友都唔敢肯定，大致係指alcohol可以溶解blood裡頭嘅fat，令到blood嘅viscosity降低(即係令d blood冇咁黏)。如果dblood黏，可能會引至血管閉塞，咁就會有heart attack。
回應(會考化學)
回應1
pele159:
1. 請問寫essay 洗唔洗寫 equation ??
2. Preparation of sulphuric acid係咪 Contact process ??
3. 如果想整 Conc. Nitric acid 可以點整呀 ?
4. 請問係咪有個新方法整 soap ( acid hydrolysis of fat or oil ) ?
Fat/oil + water <=> fatty acids + glycerol
5. 整soapless detergent 係咪要 conc.H2SO4 & NaOH 呀 ??
6. 你上次答NaOH同hydrolysis裡面形成嘅carboxylic acid neutralize生成salt of carboxylic acid(即係soap) 咁我英文可以點答呀 ??
7. 請問點解 soap 係 alkaline ( 佢又冇OH-ion ) ?
化學友:
1. 寫essay 係唔洗寫 equation，因為essay係考communication skill (傳意技能)，以文字表達chemical knowledge。除非係題目要求，平日係唔使寫equation嘅，仲要記住唔好以point form寫出，真係會扣分o架。
6. pele159，睇吓咁樣寫O唔OK: NaOH neutralize the carboxylic acid formed to give sodium salt of carboxylic acid which is the soap.
7. 因為當soap溶咗落水，佢會同水有化學化應生忒OH-。雖然條equation out c，但係都寫比你睇下啦: RCOO- (soap) + H2O <=> RCOOH + OH-
回應2
Maryuen:
1. 化學友，我想知道怎麼看CH3CO2H->CH3CH2OH的oxidation no.?? oxidation no.是什麼??
2. 1998 5: how to use the test tube given? wt is the answer in the marking scheme?
3. 7aiii3: why ethanol can dissolve unpolymerized monomer (vinyl chloride)?(joint us answer)
4. 7bii3: PVC is not suitable for making electric socket since the current pass through it will produce heat and melt it??
5. 9aiii: how to write the equation with [O] for the reaction between propan-1-ol and acidified potassium dichromate solution?
6. 9avi1: State TWO observable changes when the contents of the test tube (ester) were added to the sodium carbonate solution.
can i write a thin colourless layer form on top of the sodium carbonate solution??
化學友:
1. 要計到e d oxidation no. 需要d F.6 嘅concept。 化學友記得e條係pastpaper mc，其實你可以simple d 咁睇: CH3CH2OH --> CH3COOH (ethanol --> ethanoic acid)係oxidation，所以CH3COOH --> CH3CH2OH就係相反嘅reduction。
2. d test tubes 係用o黎裝d chemicals嘅
3. 因為vinyl chloride同埋ethanol都係organic compounds，化學友唸你老師應該教過'like dissolves like'嘅concept，所以ethanol可以dissolve vinyl chloride。
4. 正確d o黎講係防止火警時高溫會 melt 咗d PVC，咁copper wire外露會非常dangerous，引至explosion或漏電。
5. maryeun，你係唔係想問e絛equation: CH3CH2CH2OH + [O] à CH3CH2COOH ?
6. 係可以o架，因為ester係insoluble in water，而且浮o向水面。
pele159:
1. 請問寫essay 洗唔洗寫 equation ??
2. Preparation of sulphuric acid係咪 Contact process ??
3. 如果想整 Conc. Nitric acid 可以點整呀 ?
4. 請問係咪有個新方法整 soap ( acid hydrolysis of fat or oil ) ?
Fat/oil + water <=> fatty acids + glycerol
5. 整soapless detergent 係咪要 conc.H2SO4 & NaOH 呀 ??
6. 你上次答NaOH同hydrolysis裡面形成嘅carboxylic acid neutralize生成salt of carboxylic acid(即係soap) 咁我英文可以點答呀 ??
7. 請問點解 soap 係 alkaline ( 佢又冇OH-ion ) ?
化學友:
1. 寫essay 係唔洗寫 equation，因為essay係考communication skill (傳意技能)，以文字表達chemical knowledge。除非係題目要求，平日係唔使寫equation嘅，仲要記住唔好以point form寫出，真係會扣分o架。
2. 係呀，整sulphuric acid嘅industrial process係指Contact process(接觸法)。
3. 整conc. nitric acid嘅industrial process已經out c喇，不過都俾你參考吓啦!
首先係catalytic oxidation of ammonia (氨嘅催化氧化)，用Cu or Pt做catalyst。
4NH3(g) + 5O2(g) -->4NO(g) + 6H2O(g)
跟住NO再同空氣中嘅O2react生成NO2
2NO(g) + O2(g) --> 2NO2(g)
最後dissolve NO2落水就製成HNO3
4NO2(g) + O2(g) + 2H2O(l) --> 4HNO3(aq)
4. 唔係呀pele159，fatty acid係唔同soap，fatty acid係 carboxylic acid，佢唔溶於水。而soap係ionic compound，佢溶於水先至有清潔效能。化學友估你可能同ester 嘅acidic or alkaline hydrolysis撈亂咗，無錯fat/oil係ester，佢哋係可以carry out acidic or alkaline hydrolysis。但係當fat/oil carry out acidic hydrolysis，就只會出咗隻唔溶於水嘅fatty acid，呢隻compound係唔會有cleaning power。如果fat/oil carry out alkaline hydrolysis，就會出soap。
5.係呀，petroleum fraction + conc. H2SO4，然後加入NaOH，就會做成soapless detergent。6. pele159，睇吓咁樣寫O唔OK: NaOH neutralize the carboxylic acid formed to give sodium salt of carboxylic acid which is the soap.
7. 因為當soap溶咗落水，佢會同水有化學化應生忒OH-。雖然條equation out c，但係都寫比你睇下啦: RCOO- (soap) + H2O <=> RCOOH + OH-
回應2
Maryuen:
1. 化學友，我想知道怎麼看CH3CO2H->CH3CH2OH的oxidation no.?? oxidation no.是什麼??
2. 1998 5: how to use the test tube given? wt is the answer in the marking scheme?
3. 7aiii3: why ethanol can dissolve unpolymerized monomer (vinyl chloride)?(joint us answer)
4. 7bii3: PVC is not suitable for making electric socket since the current pass through it will produce heat and melt it??
5. 9aiii: how to write the equation with [O] for the reaction between propan-1-ol and acidified potassium dichromate solution?
6. 9avi1: State TWO observable changes when the contents of the test tube (ester) were added to the sodium carbonate solution.
can i write a thin colourless layer form on top of the sodium carbonate solution??
化學友:
1. 要計到e d oxidation no. 需要d F.6 嘅concept。 化學友記得e條係pastpaper mc，其實你可以simple d 咁睇: CH3CH2OH --> CH3COOH (ethanol --> ethanoic acid)係oxidation，所以CH3COOH --> CH3CH2OH就係相反嘅reduction。
2. d test tubes 係用o黎裝d chemicals嘅
3. 因為vinyl chloride同埋ethanol都係organic compounds，化學友唸你老師應該教過'like dissolves like'嘅concept，所以ethanol可以dissolve vinyl chloride。
4. 正確d o黎講係防止火警時高溫會 melt 咗d PVC，咁copper wire外露會非常dangerous，引至explosion或漏電。
5. maryeun，你係唔係想問e絛equation: CH3CH2CH2OH + [O] à CH3CH2COOH ?
6. 係可以o架，因為ester係insoluble in water，而且浮o向水面。
2007年4月28日 星期六
回應(會考化學)
回應1
Yin ni:
我mc卡住係30-35 ge range
係呢3日有咩方法可以提升呢?
做左97-05pp 了
做多次有效嗎?
化學友:
yin ni，30 - 35條mc大約得到C-D grade。化學友suggest你將所有錯嘅mc再做多幾次(唔使全部再做，冇咁多時間o架啦)，你應該會發覺成日都係錯類似嘅o野，o個d就係你嘅弱項，會令你mc一路冇乜進步。主攻改善弱項應該會令你有明顯嘅improvement。跟住去明報o個website download幾份mock做practice丫:
http://life.mingpao.com/htm/hkcee2007/cfm/main1.cfm
化學友覺得咁樣會最effective。盡力啦yin ni，化學友以前有d學生mc都係卡住o向30-35，但係佢地跟住化學友講嘅咁做，最後都得到B。
回應2
Cathy:
我想問有關1998年既paper1既6ai/2
唔係standard solution放係burette到咩???我想知邊樣放係burette同conical flask呢???
化學友:
Cathy，standard solution一定要放o向burette到係好多年前嘅做法，e家standard solution可以放o向burette或者conical flask都得o架。
回應3
小白:
您好，有些問題想問您：
Q1在會考中，泡騰現象是否專來形容生成二氧化碳氣體。
Q2Ca(OH)2，CaCO3，它們是微溶於水，但寫化學式時卻有時是(s)，有時是(aq)....怎麼區分。還有...是不是只有Mg跟Ca會微溶於水??
Q3：除了氮外還有甚麼氣體不溶於水，所有貴氣體？(會考程度)
Q4：溴與碘溶液作電解時，只有極稀濃度時才不會優先放電嗎？還是說稀時也不能= ="?
Q5：鍚還是鐵活潑？錫與鋅還有甚麼分別(除了鋅有毒)，因為做了一題MC說鍍錫不宜作防止鐵船生銹，但鋅卻可以。
Q6：為甚麼肥皂容易被生物降解，不是說只有沒有支鏈才容易被生物降解嗎？但肥皂必定沒有支鏈的嗎？
Q7：金屬氧化物加熱能夠生生成氧氣的就只有汞(II)嗎？銅的煅燒跟直接加熱有甚麼不同嗎？
化學友:
1. 唔係呀。凡親一個reaction出好多gas bubbles就叫做泡騰(effervescence)。所以Ca+ 2H2O ---> Ca(OH)2 + H2 都可以叫泡騰。
2. 小白，其實(aq)同埋(s)都correct。如果你e家覺得唔知幾時寫(aq)或者(s)，化學友suggest你CE chem時唔好寫state symbol，因為唔會扣分o架。
Metal當中只有K, Na同埋Ca會溶水(佢地同水react產生metal hydroxide，而metal hydroxide溶o向水到)，其他metal唔會溶水。
3. H2, N2, CO同埋所有noble gases(貴氣體):唔溶水
O2, CO2, Cl2: 少少溶水
4. 其實你做街外買嘅exercise時，有時唔知幾時會出I2幾時會出O2。但CE chem會好明顯: conc. NaI就出I2，至於very dil. NaI就出O2。dil. NaI就有時出I2，有時出O2，但條question會明示想你寫邊o個答案。
5. Zn(鋅) is more reactive than Fe而Fe is more reactive than Sn(錫) (活潑性:Zn>Fe>Sn)。
因為防止鐵船生銹係用sacrificial protection(犧牲性保護)，所以一定要用一隻活潑過Fe嘅metal例如Zn做protection。
6.小白你完全correct呀。只有冇支鏈嘅先容易被生物降解，而所有肥皂一定冇支鏈o架。
7. 仲有Ag2O遇埶會生成氧氣呀(2Ag2O --> 4Ag + O2)。Cu直接加埶生成CuO (2Cu + O2 --> 2CuO)。而Cu metal冇煅燒o架，煅燒(roasting)係形容化合物o向空氣度加熱，Cu metal係elemnt，所以冇煅燒。
明白嗎小白?
Yin ni:
我mc卡住係30-35 ge range
係呢3日有咩方法可以提升呢?
做左97-05pp 了
做多次有效嗎?
化學友:
yin ni，30 - 35條mc大約得到C-D grade。化學友suggest你將所有錯嘅mc再做多幾次(唔使全部再做，冇咁多時間o架啦)，你應該會發覺成日都係錯類似嘅o野，o個d就係你嘅弱項，會令你mc一路冇乜進步。主攻改善弱項應該會令你有明顯嘅improvement。跟住去明報o個website download幾份mock做practice丫:
http://life.mingpao.com/htm/hkcee2007/cfm/main1.cfm
化學友覺得咁樣會最effective。盡力啦yin ni，化學友以前有d學生mc都係卡住o向30-35，但係佢地跟住化學友講嘅咁做，最後都得到B。
回應2
Cathy:
我想問有關1998年既paper1既6ai/2
唔係standard solution放係burette到咩???我想知邊樣放係burette同conical flask呢???
化學友:
Cathy，standard solution一定要放o向burette到係好多年前嘅做法，e家standard solution可以放o向burette或者conical flask都得o架。
回應3
小白:
您好，有些問題想問您：
Q1在會考中，泡騰現象是否專來形容生成二氧化碳氣體。
Q2Ca(OH)2，CaCO3，它們是微溶於水，但寫化學式時卻有時是(s)，有時是(aq)....怎麼區分。還有...是不是只有Mg跟Ca會微溶於水??
Q3：除了氮外還有甚麼氣體不溶於水，所有貴氣體？(會考程度)
Q4：溴與碘溶液作電解時，只有極稀濃度時才不會優先放電嗎？還是說稀時也不能= ="?
Q5：鍚還是鐵活潑？錫與鋅還有甚麼分別(除了鋅有毒)，因為做了一題MC說鍍錫不宜作防止鐵船生銹，但鋅卻可以。
Q6：為甚麼肥皂容易被生物降解，不是說只有沒有支鏈才容易被生物降解嗎？但肥皂必定沒有支鏈的嗎？
Q7：金屬氧化物加熱能夠生生成氧氣的就只有汞(II)嗎？銅的煅燒跟直接加熱有甚麼不同嗎？
化學友:
1. 唔係呀。凡親一個reaction出好多gas bubbles就叫做泡騰(effervescence)。所以Ca+ 2H2O ---> Ca(OH)2 + H2 都可以叫泡騰。
2. 小白，其實(aq)同埋(s)都correct。如果你e家覺得唔知幾時寫(aq)或者(s)，化學友suggest你CE chem時唔好寫state symbol，因為唔會扣分o架。
Metal當中只有K, Na同埋Ca會溶水(佢地同水react產生metal hydroxide，而metal hydroxide溶o向水到)，其他metal唔會溶水。
3. H2, N2, CO同埋所有noble gases(貴氣體):唔溶水
O2, CO2, Cl2: 少少溶水
4. 其實你做街外買嘅exercise時，有時唔知幾時會出I2幾時會出O2。但CE chem會好明顯: conc. NaI就出I2，至於very dil. NaI就出O2。dil. NaI就有時出I2，有時出O2，但條question會明示想你寫邊o個答案。
5. Zn(鋅) is more reactive than Fe而Fe is more reactive than Sn(錫) (活潑性:Zn>Fe>Sn)。
因為防止鐵船生銹係用sacrificial protection(犧牲性保護)，所以一定要用一隻活潑過Fe嘅metal例如Zn做protection。
6.小白你完全correct呀。只有冇支鏈嘅先容易被生物降解，而所有肥皂一定冇支鏈o架。
7. 仲有Ag2O遇埶會生成氧氣呀(2Ag2O --> 4Ag + O2)。Cu直接加埶生成CuO (2Cu + O2 --> 2CuO)。而Cu metal冇煅燒o架，煅燒(roasting)係形容化合物o向空氣度加熱，Cu metal係elemnt，所以冇煅燒。
明白嗎小白?
會考化學(11)
係第三章Metal(金屬)裡面，同學仔要留意以下幾點。
1. Ca放在進水裡嘅observation: Ca沉於水及有colourless gas釋出，記住絕無brick-red flame(磚紅色火焰)，只有Na同埋K遇水先會有yellow同埋lilac flame。留意下面嘅pastpaper:
200o paper I 9a
2003 paper I 2
2004 Paper I 1
2000 Paper II 33
2. 會考寫equation唔使寫state symbol，唔會扣分。(除非條題寫明要寫state symbol)
3. Anodized aluminium(陽極氧化鋁)只會加強corrosion resistant (抗腐蝕 性)，並唔會加強佢嘅strength。同埋鋁嘅usage係同佢係最高蘊藏量無關。 留意下面嘅pastpaper:
1993 Paper I 1a
2001 Paper I 5
2005 年 Paper II 48
係第四章Acid and base(酸和鹼)裡面，同學留意以下幾點:
1. 測試ammonia(氨)的方法：NH3能將moist red litmus paper(濕潤的紅色石蕊 試紙)轉為blue(藍色)。留意下面嘅pastpaper:
2005 年 Paper I 12
2006 年 Paper I 4
2. Metal ions+ hydroxide ion (from NaOH或者NH3) --> precipitation 。e種reaction叫做precipitation reaction(沉澱反應)
Equation Colour of precipitate
Zn2+(aq) + 2OH-(aq) --> Zn(OH)2(s) white
Pb2+(aq) + 2OH-(aq) --> Pb(OH)2(s) white
Al3+(aq) + 3OH-(aq) --> Al(OH)3(s) white
Cu2+(aq) + 2OH-(aq) --> Cu(OH)2(s) blue
Fe2+(aq) + 2OH-(aq) --> Fe(OH)2(s) dirty-green
Ni2+(aq) + 2OH-(aq) --> Ni(OH)2(s) bluish-green
Fe3+(aq) + 3OH-(aq) --> Fe(OH)3(s) brown
Cr3+(aq) + 3OH-(aq) --> Cr(OH)3(s) green
仲有Al(OH)3, Zn(OH)2 and Pb(OH)2 dissolve in excess NaOH，而Zn(OH)2同埋Cu(OH)3 dissolve in excess NH3。留意下面嘅pastpaper:
2001 年 Paper I 2b
2003 年 Paper I 8b
2005 年 Paper I 4c
3. Cu同alkanoic acid(烷酸)、dilute hydrochloric acid(稀氫氯酸)同埋dilute sulphuric acid (稀硫酸)係冇化反應o架(d考生一考試就成日錯o架啦)。留意下面嘅pastpaper:
2005 年 Paper I 3b
2005 年 Paper II 38
4. Acid-base titration (中和滴定) 嘅mole calculation (摩爾計算題)同埋 experimental procedure(實驗過程)。差唔多年年都考。留意會考化學(7)。
5. 當然仲有rate of reaction啦，今年大機呀。留意會考化學(7)。
1. Ca放在進水裡嘅observation: Ca沉於水及有colourless gas釋出，記住絕無brick-red flame(磚紅色火焰)，只有Na同埋K遇水先會有yellow同埋lilac flame。留意下面嘅pastpaper:
200o paper I 9a
2003 paper I 2
2004 Paper I 1
2000 Paper II 33
2. 會考寫equation唔使寫state symbol，唔會扣分。(除非條題寫明要寫state symbol)
3. Anodized aluminium(陽極氧化鋁)只會加強corrosion resistant (抗腐蝕 性)，並唔會加強佢嘅strength。同埋鋁嘅usage係同佢係最高蘊藏量無關。 留意下面嘅pastpaper:
1993 Paper I 1a
2001 Paper I 5
2005 年 Paper II 48
係第四章Acid and base(酸和鹼)裡面，同學留意以下幾點:
1. 測試ammonia(氨)的方法：NH3能將moist red litmus paper(濕潤的紅色石蕊 試紙)轉為blue(藍色)。留意下面嘅pastpaper:
2005 年 Paper I 12
2006 年 Paper I 4
2. Metal ions+ hydroxide ion (from NaOH或者NH3) --> precipitation 。e種reaction叫做precipitation reaction(沉澱反應)
Equation Colour of precipitate
Zn2+(aq) + 2OH-(aq) --> Zn(OH)2(s) white
Pb2+(aq) + 2OH-(aq) --> Pb(OH)2(s) white
Al3+(aq) + 3OH-(aq) --> Al(OH)3(s) white
Cu2+(aq) + 2OH-(aq) --> Cu(OH)2(s) blue
Fe2+(aq) + 2OH-(aq) --> Fe(OH)2(s) dirty-green
Ni2+(aq) + 2OH-(aq) --> Ni(OH)2(s) bluish-green
Fe3+(aq) + 3OH-(aq) --> Fe(OH)3(s) brown
Cr3+(aq) + 3OH-(aq) --> Cr(OH)3(s) green
仲有Al(OH)3, Zn(OH)2 and Pb(OH)2 dissolve in excess NaOH，而Zn(OH)2同埋Cu(OH)3 dissolve in excess NH3。留意下面嘅pastpaper:
2001 年 Paper I 2b
2003 年 Paper I 8b
2005 年 Paper I 4c
3. Cu同alkanoic acid(烷酸)、dilute hydrochloric acid(稀氫氯酸)同埋dilute sulphuric acid (稀硫酸)係冇化反應o架(d考生一考試就成日錯o架啦)。留意下面嘅pastpaper:
2005 年 Paper I 3b
2005 年 Paper II 38
4. Acid-base titration (中和滴定) 嘅mole calculation (摩爾計算題)同埋 experimental procedure(實驗過程)。差唔多年年都考。留意會考化學(7)。
5. 當然仲有rate of reaction啦，今年大機呀。留意會考化學(7)。
會考化學(10)
今日開始想同同學仔講吓每個Chapter重要嘅位，唔好睇小e d points呀，如果同學仔守住e d points唔錯嘅話，可能可以攞高一個grade。
係第一章大氣(atmosphere)裡面，同學會對熔點、沸點與物質三態嘅關係都會容易混淆，所以係會考成日出o架。
熔點(melting point)係指物質由固態轉成液態嘅溫度(solid --> liquid)。如果果樣物質嘅熔點係高過25°C，佢就係固體o黎。
沸點(boiling point)係指物質由液態轉成氣態嘅溫度(liquid --> gas)。如果果樣物質嘅沸點係低過25°C，佢就係氣體o黎。
如果25°C係位於果樣物質嘅沸點同熔點之間，佢就係液體o黎。
你可能會覺得化學友咁淺嘅o野都講，有冇攪錯呀。但係化學友發覺每次考e樣o野，d同學仔就勁錯wor。想知自已識唔識，就做下面幾條mc丫，其中有d係奸奸地:
1. 2004 PaperII 29
2. 2005 Paper II 3
3. 2006 Paper II 6
另外一樣要留意就係問過裝石灰水Ca(OH)2果樽口果d白色固體係咩黎? 答案就係CaCO3。係由於石灰水同空氣嘅CO2反應而成(Ca(OH)2 + CO2 -->CaCO3 + H2O)。睇吓e條mc 2004 Paper II 11。
至於第二章Microscopic world(微觀世界)裡面，同學仔記住留意下面幾點:
1. Definition of isotopes(同位素定義) - Atoms of same element which have the same number of protons but they have different number of neutrons. (相同元素內的不同原子，它們之間有相同的質子但有不同的中子數目。)
2. 留意1998 Paper II 1同埋2002 Paper II 1,關於electronic arrangement (電子排佈)，有d tricky。
4. 留意一d平日o向書本甚少見到嘅化合物嘅電子結構圖畫法。例如:S2Cl2 and H2O2(d考生成日畫錯e兩個圖o架:
係第一章大氣(atmosphere)裡面，同學會對熔點、沸點與物質三態嘅關係都會容易混淆，所以係會考成日出o架。
熔點(melting point)係指物質由固態轉成液態嘅溫度(solid --> liquid)。如果果樣物質嘅熔點係高過25°C，佢就係固體o黎。
沸點(boiling point)係指物質由液態轉成氣態嘅溫度(liquid --> gas)。如果果樣物質嘅沸點係低過25°C，佢就係氣體o黎。
如果25°C係位於果樣物質嘅沸點同熔點之間，佢就係液體o黎。
你可能會覺得化學友咁淺嘅o野都講，有冇攪錯呀。但係化學友發覺每次考e樣o野，d同學仔就勁錯wor。想知自已識唔識，就做下面幾條mc丫，其中有d係奸奸地:
1. 2004 PaperII 29
2. 2005 Paper II 3
3. 2006 Paper II 6
另外一樣要留意就係問過裝石灰水Ca(OH)2果樽口果d白色固體係咩黎? 答案就係CaCO3。係由於石灰水同空氣嘅CO2反應而成(Ca(OH)2 + CO2 -->CaCO3 + H2O)。睇吓e條mc 2004 Paper II 11。
至於第二章Microscopic world(微觀世界)裡面，同學仔記住留意下面幾點:
1. Definition of isotopes(同位素定義) - Atoms of same element which have the same number of protons but they have different number of neutrons. (相同元素內的不同原子，它們之間有相同的質子但有不同的中子數目。)
2. 留意1998 Paper II 1同埋2002 Paper II 1,關於electronic arrangement (電子排佈)，有d tricky。
3. 留意1998 Paper II 33、1999 PaperII 11同埋2001 Paper II 18,佢地好相似o架，係關於structures and properties，有機會番炒。
4. 留意一d平日o向書本甚少見到嘅化合物嘅電子結構圖畫法。例如:S2Cl2 and H2O2(d考生成日畫錯e兩個圖o架:
2007年4月27日 星期五
會考化學(9)
頭先收到Clara電話(化學友嘅F5學生，佢成績一向都好好)，佢話好擔心，因為做左成七，八份mock exercise，long question就做得幾好，但係mc一般就只係o岩得43條左右(一般o黎講，CE chem mc最少要o岩45條先會A)。其實clara太擔心o者，化學友對佢就好有信心喇，佢應該會A嘅。因為好似2006年咁，化學友就只係得14個學生o向mc獲A，但係turn out出o黎就有21個人A，類似現象2005同埋2004都一樣。咁即係話，化學友獲A嘅學生o向long question嘅表現足以compensate左mc嘅失分。所以，同學仔記住要用多d時間practise long question，因為long question對你得到乜o野grade比mc重要得多。(同學仔可能會問點解化學友會知有幾多人mc獲A。其實每間學校每年比少少$，就可以知道學生o向會考每科mc嘅表現。)
會考化學(8)
同學仔唔好意思，因最近好忙，所以化學友post d 考試攻略同埋回覆問題比較慢，化學友e兩日如果有時間會寫多d o野o架喇。大家一齊add oil啦!!
今次化學友想同同學仔講吓paragraph length(段落式) question(一般人叫e d題目做essay)，大家一定要對佢嘅出法要有d認識。同學仔做過05同埋06pastpaper都知道卷一有兩條呢d題目，一條出自核心部份而另一條出自延展部份。一般o黎講每條佔9分，6分係內容分而3分係傳意技能(communication)。
通常6分內容分即係要答6個points，記住at least要寫到6個points先好停手。仲有訝chem essay唔使要求你寫引子同埋結尾o架，所以唔好waste time去寫呀‧
至於傳意技能嘅3分係依據以下條件俾分：
1分係俾以paragraph length寫出(即使唔係用point form或者table，而係一段一段咁寫出o黎)
另1分係俾文章嘅前文後理通唔通順(如果用english寫essay，accuracy of using english都計埋o架)
最後1分係俾無化學知識上嘅失誤(例如你寫combustion of fuel in factories會產生CO2, SO2，而CO2 同埋SO2會引至global warming就會冇左e一分，因為SO2係唔會引至global warming)
至於今年化學友嘅熱門心水題包括
核心部份:
(i) Metal extraction (金屬提取);
(ii) Neutralization (中和作用);
(iii) Preparation of chlorine bleach and its reactions (氯漂白水製備及反應);
(iv) Preparation of sulphuric acid and its reactions (硫酸製備及反應);
(v) Distinguish different types of organic compounds (辨別不同類型有機化合物)
延展部份:
(i) Aluminium corrosion and anodization (鋁的腐蝕及陽極氧化);
(ii) Design experiment related to titration (設計與滴定法有關實驗);
(iii) Design experiment on rate of reaction (設計反應速率實驗)
(iv) Compare and contrast of soapy and soapless detergent (比較皂性與非皂性清潔 劑)
最後要remind同學仔:
1. 寫essay要用complete sentence。
2. 盡量唔好寫symbol或者formula，要寫全名，例如唔好寫C同埋NO要寫carbon同埋nitrogen oxide。
3. 一般唔好用多過十分鐘寫一條essay，你會冇時間做其他題目o架。
今次化學友想同同學仔講吓paragraph length(段落式) question(一般人叫e d題目做essay)，大家一定要對佢嘅出法要有d認識。同學仔做過05同埋06pastpaper都知道卷一有兩條呢d題目，一條出自核心部份而另一條出自延展部份。一般o黎講每條佔9分，6分係內容分而3分係傳意技能(communication)。
通常6分內容分即係要答6個points，記住at least要寫到6個points先好停手。仲有訝chem essay唔使要求你寫引子同埋結尾o架，所以唔好waste time去寫呀‧
至於傳意技能嘅3分係依據以下條件俾分：
1分係俾以paragraph length寫出(即使唔係用point form或者table，而係一段一段咁寫出o黎)
另1分係俾文章嘅前文後理通唔通順(如果用english寫essay，accuracy of using english都計埋o架)
最後1分係俾無化學知識上嘅失誤(例如你寫combustion of fuel in factories會產生CO2, SO2，而CO2 同埋SO2會引至global warming就會冇左e一分，因為SO2係唔會引至global warming)
至於今年化學友嘅熱門心水題包括
核心部份:
(i) Metal extraction (金屬提取);
(ii) Neutralization (中和作用);
(iii) Preparation of chlorine bleach and its reactions (氯漂白水製備及反應);
(iv) Preparation of sulphuric acid and its reactions (硫酸製備及反應);
(v) Distinguish different types of organic compounds (辨別不同類型有機化合物)
延展部份:
(i) Aluminium corrosion and anodization (鋁的腐蝕及陽極氧化);
(ii) Design experiment related to titration (設計與滴定法有關實驗);
(iii) Design experiment on rate of reaction (設計反應速率實驗)
(iv) Compare and contrast of soapy and soapless detergent (比較皂性與非皂性清潔 劑)
最後要remind同學仔:
1. 寫essay要用complete sentence。
2. 盡量唔好寫symbol或者formula，要寫全名，例如唔好寫C同埋NO要寫carbon同埋nitrogen oxide。
3. 一般唔好用多過十分鐘寫一條essay，你會冇時間做其他題目o架。
回應(會考化學)
回應
Maryuen:
1. 我還想知道dilution of acid/alkali是不是都是exothermic?而dissolve NaOH pellets in water呢??can you explain?
2. polyvinyl chloride是可以用來make electrical insulaton for wires,但它不是thermosetting plastic,這樣都可以嗎??
3. wt is topax?(out c?)wt is monosodium glutamate?(out c?)wt is bronze?(out c?)
4. 是不是all non-metal produce acidic oxide?
化學友:
1. Yes ah。diliuting conc. acid、conc. alkali或者NaOH pellets都係exothermic (一般會考唔會問diluting dil. acid或dil. alkali，因為可能冇熱放出。所以考試一定係diluting conc. acid and conc. alkali)。
至於explanation呢就真係out c，要o向AL chem先會學。CE 程度好難解釋，而且唔會考o架。
2.係可以o架。因為thermosetting plastic好hard同埋rigid (因為有cross-link)，如果用佢o黎做insulation for wire，咁條電 線咪唔彎曲得同埋轉彎lor。所以insulation layer for wire都係要用thermoplastic o黎做，因為佢冇咁hard同埋rigid。
3. 冇錯呀，全部都out c o架。
4. 大部份non-metal oxides都係acidic，例如，CO2, SO2, SO3, NO2, Cl2O....etc。但係有小部份唔係，例如CO同埋NO就係neutral而唔係acidic。
(P.S. CO, CO, SO2, SO3, NO, NO2, Cl2O e幾隻oxides係CE常見嘅non-metal oxides)
OK ma maryuen?
Maryuen:
1. 我還想知道dilution of acid/alkali是不是都是exothermic?而dissolve NaOH pellets in water呢??can you explain?
2. polyvinyl chloride是可以用來make electrical insulaton for wires,但它不是thermosetting plastic,這樣都可以嗎??
3. wt is topax?(out c?)wt is monosodium glutamate?(out c?)wt is bronze?(out c?)
4. 是不是all non-metal produce acidic oxide?
化學友:
1. Yes ah。diliuting conc. acid、conc. alkali或者NaOH pellets都係exothermic (一般會考唔會問diluting dil. acid或dil. alkali，因為可能冇熱放出。所以考試一定係diluting conc. acid and conc. alkali)。
至於explanation呢就真係out c，要o向AL chem先會學。CE 程度好難解釋，而且唔會考o架。
2.係可以o架。因為thermosetting plastic好hard同埋rigid (因為有cross-link)，如果用佢o黎做insulation for wire，咁條電 線咪唔彎曲得同埋轉彎lor。所以insulation layer for wire都係要用thermoplastic o黎做，因為佢冇咁hard同埋rigid。
3. 冇錯呀，全部都out c o架。
4. 大部份non-metal oxides都係acidic，例如，CO2, SO2, SO3, NO2, Cl2O....etc。但係有小部份唔係，例如CO同埋NO就係neutral而唔係acidic。
(P.S. CO, CO, SO2, SO3, NO, NO2, Cl2O e幾隻oxides係CE常見嘅non-metal oxides)
OK ma maryuen?
2007年4月26日 星期四
回應(會考化學)
回應
Maryuen:
(6)2004 past paper 9cii2can i use water?
(7)What is duralumin?
(8) 2003 past paper 3biwhat is formula unit stated in the marking scheme?
(9) HBr and conc. H2SO4是什麼reaction?
(10) conc. H2SO4和sugar的reaction observation要write "the heat produced expand air inside the black carbon and rise it up"嗎??
(11) conc. H2SO4 used in the preparation of HCl and HNO3 acid out c了嗎??
(12) H2SO4 ionizes in water to give H3O+(aq) ions??
(13) H2SO4的half equation到底是什麼??
化學友:
(6) 唔得o架，一定要H+。因為只有H+先會react with RCOO- (RCOO- + H+ --> RCOOH)
(7) duralum係由aluminium做成嘅alloy(合金)，佢比aluminium more corrosion resistant同埋stronger。
(8) e o個term可以唔使識o架，其實你唔使學佢咁做，用你平日計mole嘅方法做就得o架喇。
(9) maryuen，你o向邊度見到e o個reaction? 照計out out地syllabus。不過寫比你睇下:
2HBr + H2SO4 --> Br2 + SO2 + 2H2O
e o個係redox reaction(因為Br嘅O.N.由-1 change to 0; 而S嘅O.N.由+6 change to +4)
(10) 一般會考答案唔係咁寫，你只要寫成咁就得喇:
i. sugar chars (sugar turns from white to black)
ii. misty fume(H2O(g) is given out
(11) out左喇
(12) 你可睇o下下面回覆pele159嘅答案，你地問緊同一樣o野呀。
(13) H2SO4 + 2H+ + 2e- --> SO2 + 2H2O 或者 4H+ + SO42- + 2e- --> SO2 + 2H2O
第一條accurate d 但會考兩條都接受。
Maryuen:
(6)2004 past paper 9cii2can i use water?
(7)What is duralumin?
(8) 2003 past paper 3biwhat is formula unit stated in the marking scheme?
(9) HBr and conc. H2SO4是什麼reaction?
(10) conc. H2SO4和sugar的reaction observation要write "the heat produced expand air inside the black carbon and rise it up"嗎??
(11) conc. H2SO4 used in the preparation of HCl and HNO3 acid out c了嗎??
(12) H2SO4 ionizes in water to give H3O+(aq) ions??
(13) H2SO4的half equation到底是什麼??
化學友:
(6) 唔得o架，一定要H+。因為只有H+先會react with RCOO- (RCOO- + H+ --> RCOOH)
(7) duralum係由aluminium做成嘅alloy(合金)，佢比aluminium more corrosion resistant同埋stronger。
(8) e o個term可以唔使識o架，其實你唔使學佢咁做，用你平日計mole嘅方法做就得o架喇。
(9) maryuen，你o向邊度見到e o個reaction? 照計out out地syllabus。不過寫比你睇下:
2HBr + H2SO4 --> Br2 + SO2 + 2H2O
e o個係redox reaction(因為Br嘅O.N.由-1 change to 0; 而S嘅O.N.由+6 change to +4)
(10) 一般會考答案唔係咁寫，你只要寫成咁就得喇:
i. sugar chars (sugar turns from white to black)
ii. misty fume(H2O(g) is given out
(11) out左喇
(12) 你可睇o下下面回覆pele159嘅答案，你地問緊同一樣o野呀。
(13) H2SO4 + 2H+ + 2e- --> SO2 + 2H2O 或者 4H+ + SO42- + 2e- --> SO2 + 2H2O
第一條accurate d 但會考兩條都接受。
回應(會考化學)
回應1
pele159:
H3O+(aq) ions = H+ ion ?
化學友:
pele159，你係唔係o向2003 Paper I Q4嘅marking見到H3O+ e o個答案呀?其實H3O+係同H+一樣o架。你o向CE考試寫H+就得喇，H3O+ out of syllabus o架。
回應2
maryuen:
你好!化學友~之前,我問過你一些問題~可是你還未回應我~我現在多post一次,麻煩你了~
(1)就是SiO2是一個giant covalent compound嗎??如果是,那為什麼沙都是一顆顆十分細小的?它跟SO2的分別又是什麼??
(2)2004 past paper 2awhy the marking scheme say that table salt gives misty fumes?
(3)2004 past paper 6aivhow to deduce the formula?好像很難的樣子..
(4)2004 past paper 8ciiwhy rinsing the mouth can lower the concentration of ethanol in breath?
(5)how to explain that the metal is malleable in term of its structure
化學友:
maryuen, sor 呀，因為化學友o向學校好多o野做，而又幫緊d F5學生prepare CE chem，所以未有時間答你d問題，e家答住你部份問題先喇。
1. maryuen我地唔會叫SiO2做giant covalent compound，咁寫o向會考有機會扣分o架，我地應該叫佢做compound with giant covalent structure。冇錯，理倫上每粒Si同埋O atom都係用covalent bond連埋，而隻compound嘅size應該冇窮冇盡咁大。但係e d 只係理倫o黎，世界上有好多種原因e.g. weathering會將compound with giant covalent structure變細。
SO2同SiO2唔同，SO2係由molecules組成，molecules之間有van der Waals forces，而S同O之間係covalent bond。所以SO2係compound with simple molecular structure。
2.因為發生左下面o個reaction:
NaCl + H2SO4(conc) --> NaHSO4 + HCl
white fume
e o個reaction有少少out of syllabus，不過都值得知道嘅。
3. Water (H2O) is an oxide of hydrogen. Electrolysis of water in the presence of sulphuric acid gives hydrogen and oxygen in a volume ratio of 2 : 1.
(i) Suggest suitable electrodes to be used in the electrolysis.
(ii) Write the half equation for the reaction at the cathode and that at the anode during the electrolysis.
(iii) What is the function of sulphuric acid in the electrolysis?
(iv) Is it possible to deduce the formula of water from the results of the electrolysis? Explain your answer.
其實由(ii)嘅答案，你可知道how to deduce:
anode: 4OH-(aq) --> O2(g) + 2HO(l) + 4e-
cathode: 2H+(aq) + 2e- -->H2(g)
咁即係話如果有4粒e-經過circuit，就會產生一粒O2同埋兩粒H2(即係H2:O2 = 2:1)。d H2同埋O2都係由水o黎，所以H同埋Oo向水裡面嘅比例都係2:1，而formula就係H2O。
4. 原本口裡面有ethanol，rinse之後將水吐出，口裡面ethanol嘅amount就少左好多。咁樣就冇乜ethanol由口腔去到鼻腔，所以concentration of ethanol in breath decreases。
5. Metals can be considered as making up of positive ions and a ‘sea’ of delocalized electrons. The attraction between themetallic ions and the delocalized electrons holds the particles together (metallic bond). Metallic bond is non-directional. Layers of atoms can easily slide over each another. Hence, metals are malleable.
就算會考問你why metals are ductile，答案一樣。
pele159:
H3O+(aq) ions = H+ ion ?
化學友:
pele159，你係唔係o向2003 Paper I Q4嘅marking見到H3O+ e o個答案呀?其實H3O+係同H+一樣o架。你o向CE考試寫H+就得喇，H3O+ out of syllabus o架。
回應2
maryuen:
你好!化學友~之前,我問過你一些問題~可是你還未回應我~我現在多post一次,麻煩你了~
(1)就是SiO2是一個giant covalent compound嗎??如果是,那為什麼沙都是一顆顆十分細小的?它跟SO2的分別又是什麼??
(2)2004 past paper 2awhy the marking scheme say that table salt gives misty fumes?
(3)2004 past paper 6aivhow to deduce the formula?好像很難的樣子..
(4)2004 past paper 8ciiwhy rinsing the mouth can lower the concentration of ethanol in breath?
(5)how to explain that the metal is malleable in term of its structure
化學友:
maryuen, sor 呀，因為化學友o向學校好多o野做，而又幫緊d F5學生prepare CE chem，所以未有時間答你d問題，e家答住你部份問題先喇。
1. maryuen我地唔會叫SiO2做giant covalent compound，咁寫o向會考有機會扣分o架，我地應該叫佢做compound with giant covalent structure。冇錯，理倫上每粒Si同埋O atom都係用covalent bond連埋，而隻compound嘅size應該冇窮冇盡咁大。但係e d 只係理倫o黎，世界上有好多種原因e.g. weathering會將compound with giant covalent structure變細。
SO2同SiO2唔同，SO2係由molecules組成，molecules之間有van der Waals forces，而S同O之間係covalent bond。所以SO2係compound with simple molecular structure。
2.因為發生左下面o個reaction:
NaCl + H2SO4(conc) --> NaHSO4 + HCl
white fume
e o個reaction有少少out of syllabus，不過都值得知道嘅。
3. Water (H2O) is an oxide of hydrogen. Electrolysis of water in the presence of sulphuric acid gives hydrogen and oxygen in a volume ratio of 2 : 1.
(i) Suggest suitable electrodes to be used in the electrolysis.
(ii) Write the half equation for the reaction at the cathode and that at the anode during the electrolysis.
(iii) What is the function of sulphuric acid in the electrolysis?
(iv) Is it possible to deduce the formula of water from the results of the electrolysis? Explain your answer.
其實由(ii)嘅答案，你可知道how to deduce:
anode: 4OH-(aq) --> O2(g) + 2HO(l) + 4e-
cathode: 2H+(aq) + 2e- -->H2(g)
咁即係話如果有4粒e-經過circuit，就會產生一粒O2同埋兩粒H2(即係H2:O2 = 2:1)。d H2同埋O2都係由水o黎，所以H同埋Oo向水裡面嘅比例都係2:1，而formula就係H2O。
4. 原本口裡面有ethanol，rinse之後將水吐出，口裡面ethanol嘅amount就少左好多。咁樣就冇乜ethanol由口腔去到鼻腔，所以concentration of ethanol in breath decreases。
5. Metals can be considered as making up of positive ions and a ‘sea’ of delocalized electrons. The attraction between themetallic ions and the delocalized electrons holds the particles together (metallic bond). Metallic bond is non-directional. Layers of atoms can easily slide over each another. Hence, metals are malleable.
就算會考問你why metals are ductile，答案一樣。
2007年4月24日 星期二
回應(會考化學)
回應
pele159:
你好 我有少少問題
1. 請問 detergent 有 branch 係咪唔 可以溶在水 ??不過點 g 稱為有 branch ??
2. solid citric acid 點解可以 turn moist blue litmus paper red ??
3. 請問整soap 中的 NaOH/H2SO4 係咪catalyst ??我呀sir 話係,不過我問同學,佢地又say no
4. Refer to 03 第9(a)題如果the inert electrode A is copper plate , the B is zinc rod .Sulphur is ZnSO4, sodium is CuSO4 In what the direction would the sulphate ion pass through the porus pot ? Explain your ans .
你可否比一比你個e-mail 我 ??我有圖但唔識 upload,問唔到 ....
化學友:
pele159，答住你部份題目先啦，因為而家畫唔到圖呀。
2. 因為moist blue litmus paper上面有水(即係moist)，部份solid citric acid dissolve o向d水到give out H+ ion，所以moist blue litmus paper turns red。
3.pele159，製造soap係要用NaOH(但係唔使用H2SO4；H2SO4係用嚟做soapless detergent)。NaOH有兩個作用:
i. as a catalyst in the hydrolysis of fat/oil
ii. 同hydrolysis裡面形成嘅carboxylic acid neutralize生成salt of carboxylic acid(即係soap)。
所以你阿sir係啱o架。
4.如果好似你咁講，ZnSO4(aq)就會越嚟越多Zn2+，因為Zn electrode gradually dissolves to give Zn2+(aq)，即係e部份嘅 electrolyte越嚟越+ve(因為Zn2+多左，但係SO42-冇多到冇少到)。而CuSO4(aq)就會越嚟越少Cu2+，因為Cu2+(aq) deposites on the Cu electrode，即係e部份嘅 electrolyte越嚟越-ve(因為Cu2+少左，但係SO42-冇多到冇少到)。為左中和d charge，SO42-就會由CuSO4 move to ZnSO4，令到兩面嘅electrolytes唔會太+ve或者-ve。明唔明呀?
pele159，你可以send幅圖去e嗰email丫: friendium@gmail.com
pele159:
你好 我有少少問題
1. 請問 detergent 有 branch 係咪唔 可以溶在水 ??不過點 g 稱為有 branch ??
2. solid citric acid 點解可以 turn moist blue litmus paper red ??
3. 請問整soap 中的 NaOH/H2SO4 係咪catalyst ??我呀sir 話係,不過我問同學,佢地又say no
4. Refer to 03 第9(a)題如果the inert electrode A is copper plate , the B is zinc rod .Sulphur is ZnSO4, sodium is CuSO4 In what the direction would the sulphate ion pass through the porus pot ? Explain your ans .
你可否比一比你個e-mail 我 ??我有圖但唔識 upload,問唔到 ....
化學友:
pele159，答住你部份題目先啦，因為而家畫唔到圖呀。
2. 因為moist blue litmus paper上面有水(即係moist)，部份solid citric acid dissolve o向d水到give out H+ ion，所以moist blue litmus paper turns red。
3.pele159，製造soap係要用NaOH(但係唔使用H2SO4；H2SO4係用嚟做soapless detergent)。NaOH有兩個作用:
i. as a catalyst in the hydrolysis of fat/oil
ii. 同hydrolysis裡面形成嘅carboxylic acid neutralize生成salt of carboxylic acid(即係soap)。
所以你阿sir係啱o架。
4.如果好似你咁講，ZnSO4(aq)就會越嚟越多Zn2+，因為Zn electrode gradually dissolves to give Zn2+(aq)，即係e部份嘅 electrolyte越嚟越+ve(因為Zn2+多左，但係SO42-冇多到冇少到)。而CuSO4(aq)就會越嚟越少Cu2+，因為Cu2+(aq) deposites on the Cu electrode，即係e部份嘅 electrolyte越嚟越-ve(因為Cu2+少左，但係SO42-冇多到冇少到)。為左中和d charge，SO42-就會由CuSO4 move to ZnSO4，令到兩面嘅electrolytes唔會太+ve或者-ve。明唔明呀?
pele159，你可以send幅圖去e嗰email丫: friendium@gmail.com
chemistry in action(AL10)
講吓講吓就到syllabus最後一個topic，而星期四就考Al chem喇，同學仔頂住頂住，要盡力一戰呀!!! 今次化學友要講嘅topic，莫講話學生唔熟，就算係老師一般都覺得好陌生。e個topic就係chemistry in action。入面包括polymers, drugs同埋green chemistry。就算係外國嘅syllabus都係最近先有嘅。
Polymers有d例子係會考讀過，但係更加要留意新加嘅例子，例如，Kevlar。而且同學仔特別要留意effect of structures on different polymers e一部份，要識嘅o野包括high density polyethene同埋 low density polyethene; nylon同埋 Kelvar; vulcanization of rubber ; biodegradable plastics。 精選pastpaper:
1. 1994 PaperII 9b
2. 2004 PaperII 7a
Drugs就主要學aspirin同埋 cis-platin嘅 five stages of drug development。其實e part冇乜精選pastpaper，不過都可以做o下下面兩條:
1. 1998 paperII 6c
2. 2006 Paper II 5b
至於Green chemistry梗係 要識12個green chemistry嘅principles尤其是atom economy係大熱。Specific examples 就有decaffeination using supercritical CO2同埋 use of H2O2 in the presence of manganese based catalyst as bleaching agent。如果仲有時間可以去e個website睇吓一個green chem有關嘅 experiment:
http://www.chem.cuhk.edu.hk/S6_ResourceBK.htm(選第12個實驗 - Green chemistry: an environmentally friendly preparation of 1,6-hexanedioic acid 綠色化學：1,6-己二酸的一種環保製法。有機會考o架。)
考評局出o個份sample paper都有 d同e個topics有關嘅questions：Paper I Q.6(a) - Polymers; Paper II Q.5(c) - Drugs, Paper II Q.7(c) - Green chemistry。如果仲有時間就做下啦。
同學仔呀，e一個月化學友寫嘅嘢，真係希望對你地o向AL有d幫助啦。衷心祝你地成功呀。如果你地覺得化學友o個blog對讀chem嘅弟弟妹妹親戚朋友師妹師弟男朋友仔女朋友仔....etc有用嘅話，叫佢地多d o黎睇下丫，化學友會盡力寫多d好o野o架喇。
最後，祝你地星期四打敗AL Chem e隻怪獸啦:
Polymers有d例子係會考讀過，但係更加要留意新加嘅例子，例如，Kevlar。而且同學仔特別要留意effect of structures on different polymers e一部份，要識嘅o野包括high density polyethene同埋 low density polyethene; nylon同埋 Kelvar; vulcanization of rubber ; biodegradable plastics。 精選pastpaper:
1. 1994 PaperII 9b
2. 2004 PaperII 7a
Drugs就主要學aspirin同埋 cis-platin嘅 five stages of drug development。其實e part冇乜精選pastpaper，不過都可以做o下下面兩條:
1. 1998 paperII 6c
2. 2006 Paper II 5b
至於Green chemistry梗係 要識12個green chemistry嘅principles尤其是atom economy係大熱。Specific examples 就有decaffeination using supercritical CO2同埋 use of H2O2 in the presence of manganese based catalyst as bleaching agent。如果仲有時間可以去e個website睇吓一個green chem有關嘅 experiment:
http://www.chem.cuhk.edu.hk/S6_ResourceBK.htm(選第12個實驗 - Green chemistry: an environmentally friendly preparation of 1,6-hexanedioic acid 綠色化學：1,6-己二酸的一種環保製法。有機會考o架。)
考評局出o個份sample paper都有 d同e個topics有關嘅questions：Paper I Q.6(a) - Polymers; Paper II Q.5(c) - Drugs, Paper II Q.7(c) - Green chemistry。如果仲有時間就做下啦。
同學仔呀，e一個月化學友寫嘅嘢，真係希望對你地o向AL有d幫助啦。衷心祝你地成功呀。如果你地覺得化學友o個blog對讀chem嘅弟弟妹妹親戚朋友師妹師弟男朋友仔女朋友仔....etc有用嘅話，叫佢地多d o黎睇下丫，化學友會盡力寫多d好o野o架喇。
最後，祝你地星期四打敗AL Chem e隻怪獸啦:
回應(AL)
回應
hahayi2007:
1. 你之前有題mechanism 有無答案?是不是HONO2 的OH的O打落去H2SO4個H到,甩左水,因為H2SO4係more acidic than HONO2跟住NO2+再比double bond of benzene attack,跟住就照做落去..
2. 我想問下..atom economy如果有隻reactant 係in excess,咁係計formula mass of reactant定係mass of reactant?thx.
化學友:
1. hahayi2007，其實o個mechanism寫到下面咁就滿分o架啦:
2. 任何時間都係用formula mass of reactants o黎計o架。
hahayi2007:
1. 你之前有題mechanism 有無答案?是不是HONO2 的OH的O打落去H2SO4個H到,甩左水,因為H2SO4係more acidic than HONO2跟住NO2+再比double bond of benzene attack,跟住就照做落去..
2. 我想問下..atom economy如果有隻reactant 係in excess,咁係計formula mass of reactant定係mass of reactant?thx.
化學友:
1. hahayi2007，其實o個mechanism寫到下面咁就滿分o架啦:
2. 任何時間都係用formula mass of reactants o黎計o架。
d block elements(AL9)
係 inorg chem裡面，d-block elements 係好重要o架。係今個syllabus只係改咗少少，取消咗d-block ions colour 嘅reason。新加嘅就有complex formation裡面嘅bidentate ligands (H2NCH2CH2NH2 同埋 C2O42-) 同埋 multidentate ligands (EDTA)。如果今年考complex formation，睇o黎都會考e d 新ligands。
同學仔要知道ligands嘅 relative strength：monodentate multidentate ligands (EDTA)。但係其實佢哋都係舊瓶新酒，e d內容係兩代前嘅syllabus都有o架啦。
同學仔，其實d block elements有好多值得做嘅pastpaper,不過化學友都盡力精選左幾條出o黎，希望精益求精啦:
1. 1992 Paper II 4a
2. 1996 Paper II 6b
3. 1998 paperII 8a
4. 1999 paper II 2d
5. 2000 PaperII 2c
6. 2003 PaperII 2b
同學仔要知道ligands嘅 relative strength：monodentate multidentate ligands (EDTA)。但係其實佢哋都係舊瓶新酒，e d內容係兩代前嘅syllabus都有o架啦。
同學仔，其實d block elements有好多值得做嘅pastpaper,不過化學友都盡力精選左幾條出o黎，希望精益求精啦:
1. 1992 Paper II 4a
2. 1996 Paper II 6b
3. 1998 paperII 8a
4. 1999 paper II 2d
5. 2000 PaperII 2c
6. 2003 PaperII 2b
2007年4月23日 星期一
回應(會考化學)
回應
pele159:
你好 我有少少問題
1. 請問 detergent 有 branch 係咪唔 可以溶在水 ??不過點 g 稱為有 branch ??
2. solid citric acid 點解可以 turn moist blue litmus paper red ??
3. 請問整soap 中的 NaOH/H2SO4 係咪catalyst ??我呀sir 話係,不過我問同學,佢地又say no
4. Refer to 03 第9(a)題如果the inert electrode A is copper plate , the B is zinc rod .Sulphur is ZnSO4, sodium is CuSO4 In what the direction would the sulphate ion pass through the porus pot ? Explain your ans .
你可否比一比你個e-mail 我 ??我有圖但唔識 upload,問唔到 ....
化學友:
pele159，答住你部份題目先啦，因為而家畫唔到圖呀。
2. 因為moist blue litmus paper上面有水(即係moist)，部份solid citric acid dissolve o向d水到give out H+ ion，所以moist blue litmus paper turns red。
3.pele159，製造soap係要用NaOH(但係唔使用H2SO4；H2SO4係用嚟做soapless detergent)。NaOH有兩個作用:
i. as a catalyst in the hydrolysis of fat/oil
ii. 同hydrolysis裡面形成嘅carboxylic acid neutralize生成salt of carboxylic acid(即係soap)。
所以你阿sir係啱o架。
4.如果好似你咁講，ZnSO4(aq)就會越嚟越多Zn2+，因為Zn electrode gradually dissolves to give Zn2+(aq)，即係e部份嘅 electrolyte越嚟越+ve(因為Zn2+多左，但係SO42-冇多到冇少到)。而CuSO4(aq)就會越嚟越少Cu2+，因為Cu2+(aq) deposites on the Cu electrode，即係e部份嘅 electrolyte越嚟越-ve(因為Cu2+少左，但係SO42-冇多到冇少到)。為左中和d charge，SO42-就會由CuSO4 move to ZnSO4，令到兩面嘅electrolytes唔會太+ve或者-ve。明唔明呀?
pele159，你可以send幅圖去e嗰email丫:friendium@gmail.com
pele159:
你好 我有少少問題
1. 請問 detergent 有 branch 係咪唔 可以溶在水 ??不過點 g 稱為有 branch ??
2. solid citric acid 點解可以 turn moist blue litmus paper red ??
3. 請問整soap 中的 NaOH/H2SO4 係咪catalyst ??我呀sir 話係,不過我問同學,佢地又say no
4. Refer to 03 第9(a)題如果the inert electrode A is copper plate , the B is zinc rod .Sulphur is ZnSO4, sodium is CuSO4 In what the direction would the sulphate ion pass through the porus pot ? Explain your ans .
你可否比一比你個e-mail 我 ??我有圖但唔識 upload,問唔到 ....
化學友:
pele159，答住你部份題目先啦，因為而家畫唔到圖呀。
2. 因為moist blue litmus paper上面有水(即係moist)，部份solid citric acid dissolve o向d水到give out H+ ion，所以moist blue litmus paper turns red。
3.pele159，製造soap係要用NaOH(但係唔使用H2SO4；H2SO4係用嚟做soapless detergent)。NaOH有兩個作用:
i. as a catalyst in the hydrolysis of fat/oil
ii. 同hydrolysis裡面形成嘅carboxylic acid neutralize生成salt of carboxylic acid(即係soap)。
所以你阿sir係啱o架。
4.如果好似你咁講，ZnSO4(aq)就會越嚟越多Zn2+，因為Zn electrode gradually dissolves to give Zn2+(aq)，即係e部份嘅 electrolyte越嚟越+ve(因為Zn2+多左，但係SO42-冇多到冇少到)。而CuSO4(aq)就會越嚟越少Cu2+，因為Cu2+(aq) deposites on the Cu electrode，即係e部份嘅 electrolyte越嚟越-ve(因為Cu2+少左，但係SO42-冇多到冇少到)。為左中和d charge，SO42-就會由CuSO4 move to ZnSO4，令到兩面嘅electrolytes唔會太+ve或者-ve。明唔明呀?
pele159，你可以send幅圖去e嗰email丫:friendium@gmail.com
Group IV(AL8)
講完晒 phy chem同 org chem後，到係時候同同學仔講 inorg chem。Inorg chem係e個syllabus改咗唔少，取消咗nitrogen 同埋sulphur兩個topics。但亦加入GroupIV e個topic。Group IV最特別係同一個group裡面嘅elements有好唔同properties。其實e o個topic都係舊瓶新酒，佢o向兩代前嘅syllabus都有o架啦。
e個topic有3個重點：
1. Interpretation of variation in melting point and boiling point of the elements in terms of structure and bonding (e個group由carbon係non-metal 到 silicon and germanium 係 semi-metals 到最後tin and lead 係metals)
經典pastpaper: 1993 Paper II 4b
2. decomposition of group IV oxides and chlorides (同學仔要知道group IV嘅compounds有兩個possible 嘅oxidation states +4同 +2；+4 嘅oxidation states stability decrease down the group; 而+2 oxidation state 嘅stability increase down the group; 佢嘅原因可以用inert pair effect 去解釋)
經典pastpaper: 1992 paper II 5b同埋1994 paper II 6
3. silicon and silicates，e part係全新內容，冇pastpaper。但係化學友發現教統局製作咗一份reference material可以幫助同學仔溫習，你地可以去e個網址睇吓:
http://cd1.emb.hkedcity.net/cd/science/chemistry/s67chem/chem.htm (click L&T activities然後o向other learning activities就會搵到Silicates 硅酸鹽嘅notes )
重點係留意silicate嘅不同嘅basic units。
e個topic有3個重點：
1. Interpretation of variation in melting point and boiling point of the elements in terms of structure and bonding (e個group由carbon係non-metal 到 silicon and germanium 係 semi-metals 到最後tin and lead 係metals)
經典pastpaper: 1993 Paper II 4b
2. decomposition of group IV oxides and chlorides (同學仔要知道group IV嘅compounds有兩個possible 嘅oxidation states +4同 +2；+4 嘅oxidation states stability decrease down the group; 而+2 oxidation state 嘅stability increase down the group; 佢嘅原因可以用inert pair effect 去解釋)
經典pastpaper: 1992 paper II 5b同埋1994 paper II 6
3. silicon and silicates，e part係全新內容，冇pastpaper。但係化學友發現教統局製作咗一份reference material可以幫助同學仔溫習，你地可以去e個網址睇吓:
http://cd1.emb.hkedcity.net/cd/science/chemistry/s67chem/chem.htm (click L&T activities然後o向other learning activities就會搵到Silicates 硅酸鹽嘅notes )
重點係留意silicate嘅不同嘅basic units。
Organic chem嘅mass spect同埋acids & bases(AL7)
新課程嘅新加 org chem. 部份仲有use of mass spectra to obtain structural information of common fragments such as R+, RCO+ and C6H5CH2+。同學仔都知mass spectrum e o個 topic不嬲都o向physical chem有o架，以前主要識molecular ion peak，relative abundance ratio同埋mass spectrometer嘅principles就OK。但係而家話明要識 fragementation ，就難左好多o架喇。化學友覺得今年AL都幾大機會會o向org chem嘅structural analysis一齊考(即係估structure呀)，每一年o向PaperII section B都會考一,兩條，而考生一般表現都唔好，所以同學仔唔好睇小e o個topic 呀。其實以前AL chem都有出過同fragmentation 有關嘅題目。雖然e條唔係太深同埋唔係organic compound嘅fragmentation，但係同學仔都值得睇下o架:
2002 Paper II Q.1(b)
如果同學仔平日冇乜做過e d題目，化學友就highly recommend你地去eo個網址睇o下(d questions嘅教統局同中大化學系合作出嘅)，非常有用o架:
http://cd1.emb.hkedcity.net/cd/science/chemistry/s67chem/chem.htm (click 'MS'就得o架喇)
Total有七條題目，Q.1-3 同R+有關; Q.4-5同RCO+有關; Q.6-7同C6H5CH2+有關。
另外係課程仲加咗兩個topics，佢哋係 organic acids and organic bases 同埋redox reactions。如果同學仔小心d對吓，其實佢哋係都係將舊syllabus重組過，有好多pastpaper關於e兩個topics。化學友比幾條好有用嘅pastpaper同學仔丫，做熟佢啦:
1. 1999 Paper II 6a
1. 2000 Paper I 6a
2. 2001 Paper II 6b
3. 2003 Paper I 6a
4. 2004 PaperII 6c
最後化學友d學生成日問iodoform test, silver mirror test, diazonium salt 係唔係 out of syllabus，係道順便同大家講埋，無錯佢哋係已經唔洗識o架啦。
加油呀同學仔!!!!
2002 Paper II Q.1(b)
如果同學仔平日冇乜做過e d題目，化學友就highly recommend你地去eo個網址睇o下(d questions嘅教統局同中大化學系合作出嘅)，非常有用o架:
http://cd1.emb.hkedcity.net/cd/science/chemistry/s67chem/chem.htm (click 'MS'就得o架喇)
Total有七條題目，Q.1-3 同R+有關; Q.4-5同RCO+有關; Q.6-7同C6H5CH2+有關。
另外係課程仲加咗兩個topics，佢哋係 organic acids and organic bases 同埋redox reactions。如果同學仔小心d對吓，其實佢哋係都係將舊syllabus重組過，有好多pastpaper關於e兩個topics。化學友比幾條好有用嘅pastpaper同學仔丫，做熟佢啦:
1. 1999 Paper II 6a
1. 2000 Paper I 6a
2. 2001 Paper II 6b
3. 2003 Paper I 6a
4. 2004 PaperII 6c
最後化學友d學生成日問iodoform test, silver mirror test, diazonium salt 係唔係 out of syllabus，係道順便同大家講埋，無錯佢哋係已經唔洗識o架啦。
加油呀同學仔!!!!
mechanism2(AL6)
化學友今日講第二個新課程嘅mechanism，佢就係carboxylic acid and its derivatives嘅nucleophilic acyl substitution。Acyl係指 -COX e個 functional group(X = Cl, OH, OCOR, OCR同埋 NH2)。 為o左區分佢同 haloalkane 嘅 nucleophilic substitution，所以同學仔記住要寫埋acyl e o個字。
其實化學友覺得e個mechanism好有用，佢能夠幫助同學仔明白點樣可以將carboxylic acid 變成佢嘅derivatives。課程指定嘅example係hydrolysis of acyl chloride。其他嘅examples就有 carboxylic acids react with thionyl chloride, alcohols, ammonia and amines同埋 acyl chlorides react with alcohols, ammonia and amines。
以下就係 hydrolysis of ethanoyl chloride 嘅mechanism，大家要記熟呀:
同學仔亦可以睇o下下面嘅simple animation丫，會令你容易d記o架:
其實化學友覺得e個mechanism好有用，佢能夠幫助同學仔明白點樣可以將carboxylic acid 變成佢嘅derivatives。課程指定嘅example係hydrolysis of acyl chloride。其他嘅examples就有 carboxylic acids react with thionyl chloride, alcohols, ammonia and amines同埋 acyl chlorides react with alcohols, ammonia and amines。
以下就係 hydrolysis of ethanoyl chloride 嘅mechanism，大家要記熟呀:
同學仔亦可以睇o下下面嘅simple animation丫，會令你容易d記o架:
2007年4月22日 星期日
回應(會考化學)
回應1
maryuen:
1. 我想知道什麼時候有depolymerizaton and 它是怎麼發生的??(有沒有example,會考有沒有機會出??)
2. 另外..2001 past paper 5那個anodization要不要寫eletrode的名?? sacrificial protection要寫example嗎??是不是所有essay都要有引入??
化學友:
1. maryuen，其實depolymerization o向近年嘅CE chem都好少好少出o架，化學友覺得就算出都會好容易嘅。你只要當佢係polymerization嘅相反就得o架o拉。例如:
睇到嗎maryeun o個reaction只係polymerization嘅相反。至於reaction conditions，一般都係high temperature同埋in the absence of air(否則d polymer會burns) 。
2. 2001 Paper I 5 : Explain why anodization, sacrificial protection and tin-plating can protect metals from corrosion. (9 marks)
maryuen，其實寫唔寫都冇問題o架，因為anodization一定係將aluminium做anode，所以唔都ok。2005嘅marking就冇要求你寫example，但係有時你唔知邊一年marking要寫example，所以化學友suggest你o向考試寫埋啦。CE chem嘅essay係唔使寫引子o架，一般9分嘅題目你寫夠6個points(6分)就滿分o架啦(其餘3分就係communication分)。關於essay嘅detail information，遲一、兩日再講比大家知丫。maryuen唔明再問我啦。
回應2
sinying:
1. 唔好意思........我想問ionization 同埋dissolve in water係點分架?HCL 係dissolve water 定ionize???咁NACL呢?
2. 我仲想問呢....Al2O3都係dehydrating agent 來的嗎?仲有d咩compond 係dehydrating agent呀??THX!!
化學友:
1. sinying，化學友唸你對一隻substance dissolves in water嘅方法唔係太了解。其實一隻substance dissolves in water係有唔同嘅途徑，下面係CE chem常見嘅,例如:
i. sugar溶落水。sugar只係simply dissolves in water，佢同水冇化學反應，溶之前佢係exist as sugar molecule，溶之後佢都係exist as sugar molecule。
ii. Na(s)溶落水。Na加落水時，Na同水產生化學反應生成NaOH(s)。而NaOH(s)係溶o向水to give NaOH(aq)，所以Na溶水係因為佢同水有化學反應。
iii. NaCl(s)溶落水。NaCl(s)裡面o個d Na+ ion同埋Cl-ion溶之前係 not mobile嘅，溶之後Na+ ion同埋Cl-ion變左mobile，同sugar一樣佢同水冇化學反應。
iv. HCl(g)溶落水。HCl(g)溶之前佢係exist as HCl molecule，溶之後發生ionisation:HCl --> H+ + Cl-，而H+同埋Cl-都係溶落水嘅。
簡單o黎講dissolve in water同ionisation冇乜關係，只不過有時一隻substance溶落水會發生ionisation咋。好似HCl咁，佢溶落水時會發生ionisation。
2. 凡親一隻substance可以將某一compound裡面嘅H同O remove 變成H2O, 佢就可以叫做dehydrating agent。CE chem syllabus裡面當我地剩係知遒conc. H2SO4係dehydrating agent，其他o個d dehydrating agent係唔使記，只要我地o向考試時見到隻substance可以將一隻compound嘅H2O remove，佢就係dehydrating agent o架喇。例如,
根據上面嘅定義，conc.H2SO4, Al2O3同埋P2O5都係dehydrating agent。唔使死記o架。答唔答到你呀sinying?
maryuen:
1. 我想知道什麼時候有depolymerizaton and 它是怎麼發生的??(有沒有example,會考有沒有機會出??)
2. 另外..2001 past paper 5那個anodization要不要寫eletrode的名?? sacrificial protection要寫example嗎??是不是所有essay都要有引入??
化學友:
1. maryuen，其實depolymerization o向近年嘅CE chem都好少好少出o架，化學友覺得就算出都會好容易嘅。你只要當佢係polymerization嘅相反就得o架o拉。例如:
睇到嗎maryeun o個reaction只係polymerization嘅相反。至於reaction conditions，一般都係high temperature同埋in the absence of air(否則d polymer會burns) 。
2. 2001 Paper I 5 : Explain why anodization, sacrificial protection and tin-plating can protect metals from corrosion. (9 marks)
maryuen，其實寫唔寫都冇問題o架，因為anodization一定係將aluminium做anode，所以唔都ok。2005嘅marking就冇要求你寫example，但係有時你唔知邊一年marking要寫example，所以化學友suggest你o向考試寫埋啦。CE chem嘅essay係唔使寫引子o架，一般9分嘅題目你寫夠6個points(6分)就滿分o架啦(其餘3分就係communication分)。關於essay嘅detail information，遲一、兩日再講比大家知丫。maryuen唔明再問我啦。
回應2
sinying:
1. 唔好意思........我想問ionization 同埋dissolve in water係點分架?HCL 係dissolve water 定ionize???咁NACL呢?
2. 我仲想問呢....Al2O3都係dehydrating agent 來的嗎?仲有d咩compond 係dehydrating agent呀??THX!!
化學友:
1. sinying，化學友唸你對一隻substance dissolves in water嘅方法唔係太了解。其實一隻substance dissolves in water係有唔同嘅途徑，下面係CE chem常見嘅,例如:
i. sugar溶落水。sugar只係simply dissolves in water，佢同水冇化學反應，溶之前佢係exist as sugar molecule，溶之後佢都係exist as sugar molecule。
ii. Na(s)溶落水。Na加落水時，Na同水產生化學反應生成NaOH(s)。而NaOH(s)係溶o向水to give NaOH(aq)，所以Na溶水係因為佢同水有化學反應。
iii. NaCl(s)溶落水。NaCl(s)裡面o個d Na+ ion同埋Cl-ion溶之前係 not mobile嘅，溶之後Na+ ion同埋Cl-ion變左mobile，同sugar一樣佢同水冇化學反應。
iv. HCl(g)溶落水。HCl(g)溶之前佢係exist as HCl molecule，溶之後發生ionisation:HCl --> H+ + Cl-，而H+同埋Cl-都係溶落水嘅。
簡單o黎講dissolve in water同ionisation冇乜關係，只不過有時一隻substance溶落水會發生ionisation咋。好似HCl咁，佢溶落水時會發生ionisation。
2. 凡親一隻substance可以將某一compound裡面嘅H同O remove 變成H2O, 佢就可以叫做dehydrating agent。CE chem syllabus裡面當我地剩係知遒conc. H2SO4係dehydrating agent，其他o個d dehydrating agent係唔使記，只要我地o向考試時見到隻substance可以將一隻compound嘅H2O remove，佢就係dehydrating agent o架喇。例如,
根據上面嘅定義，conc.H2SO4, Al2O3同埋P2O5都係dehydrating agent。唔使死記o架。答唔答到你呀sinying?
2007年4月21日 星期六
mechanism(AL5)
今日化覺友想講o下AL嘅org chem。Org chem 係今個syllabus大改咗，改以mechanism為主，每個functional group都要學一個mechanism 。其中有d都係同上一個syllabus相同，例如
1. alkane嘅free radical substitution
2. alkene嘅electrophilic addition
3. haloalkane嘅necleophilic substitution (SN1 and SN2)
4. carbonyl compound嘅nucleophilic addition
新加嘅就有
1. benzene嘅electrophilic substitution
2. carboxylic acid and its derivatives嘅nucleophilic acyl substitution。
其實e兩個mechanisms係前兩代嘅syllabus已經有o架啦。只不過係舊瓶新酒o者。
每一年AL exam都要同學仔寫其中一、兩個mechanisms，當然今年新加o個兩個就最大機會啦。所以化學友想講下e兩個mechanisms。首先，講嘅係benzene嘅electrophilic substitution，課程指定嘅example係mono-halogenation of benzene。 以下就係mono-chlorination of benzene嘅mechanism，同學仔一定一定要記熟呀:
下面係化學友做嘅simple animation，睇o下對你有冇用丫(按下先睇到):
教統局都有做咗幾個mechanisms嘅animations幫同學仔學習，可以去e個網址睇吓，做得幾好o架:
http://cd1.emb.hkedcity.net/cd/science/chemistry/s67chem/reaction_mechanism_animation_e.swf
最後就係俾條題目大家唸吓，考吓自己識唔識啦!
Methoxybenzene when treated with a mixture of concentrated HNO3 and H2SO4 gives 4-methoxy-1-nitrobenzene as one of the products. Outline a reasonable mechanism for this reaction.”
1. alkane嘅free radical substitution
2. alkene嘅electrophilic addition
3. haloalkane嘅necleophilic substitution (SN1 and SN2)
4. carbonyl compound嘅nucleophilic addition
新加嘅就有
1. benzene嘅electrophilic substitution
2. carboxylic acid and its derivatives嘅nucleophilic acyl substitution。
其實e兩個mechanisms係前兩代嘅syllabus已經有o架啦。只不過係舊瓶新酒o者。
每一年AL exam都要同學仔寫其中一、兩個mechanisms，當然今年新加o個兩個就最大機會啦。所以化學友想講下e兩個mechanisms。首先，講嘅係benzene嘅electrophilic substitution，課程指定嘅example係mono-halogenation of benzene。 以下就係mono-chlorination of benzene嘅mechanism，同學仔一定一定要記熟呀:
下面係化學友做嘅simple animation，睇o下對你有冇用丫(按下先睇到):
教統局都有做咗幾個mechanisms嘅animations幫同學仔學習，可以去e個網址睇吓，做得幾好o架:
http://cd1.emb.hkedcity.net/cd/science/chemistry/s67chem/reaction_mechanism_animation_e.swf
最後就係俾條題目大家唸吓，考吓自己識唔識啦!
Methoxybenzene when treated with a mixture of concentrated HNO3 and H2SO4 gives 4-methoxy-1-nitrobenzene as one of the products. Outline a reasonable mechanism for this reaction.”
2007年4月20日 星期五
會考化學(7)
同學仔，化學友o向之前分析左今年CE chem熱門嘅topics。但係記住呀除左o個d之外，仲有下面e幾個topics差o吾多年年都出o架，化學友比幾條typical pastpaper你o地，一定要做熟佢先好去考試呀。
titration(滴定):
1.1999 Paper I 7b
2. 2003 Paper I 8b
3. 2004 Paper I 7a
rate of reaction(反應速率):
1. 1994 Paper I 8
2. 2004 Paper I 8
electrolysis(電解):
1.2001 Paper I 9
2.2003 Paper I 7
2. 2005 Paper I 9
molar volume (摩爾體積):
1. 1998 Paper I 7b
2. 2000 Paper I 9a
3. 2002 Paper I 8a
化學友長氣咁講多次，記住做熟佢呀!!! 最後，記住做埋2005同埋2006嘅pastpaper，都有機返炒o架。下次化學友會同同學仔講下paragraphy-length question即係esaay呀。
回應(會考化學)
回應
Maryuen:
你好,化學友我想問C4H9OH->C4H8+H2O這個reaction什麼時候會發生??有沒有depolymerizaation??
化學友:
maryuen，我唸你e條問題同2004年CE chem mc差o吾多一樣:
2004 Paper II 27
Ethene can be prepared by heating ethanol with excess concentrated sulphuric acid. The reaction involved can be represented by the equation:
CH3CH2OH --> CH2=CH2 + H2O
The type of reaction involved in the preparation is
A. cracking.
B. condensation.
C. addition.
D. dehydration.
答案係D。e o個reaction有少少out of syllabus，但係你見到reaction之後ethanol(CH3CH2OH)會唔見左o個水(H2O)變成ethene，所以e o個reaction定為dehydration(脫水反應)。
Maryuen:
你好,化學友我想問C4H9OH->C4H8+H2O這個reaction什麼時候會發生??有沒有depolymerizaation??
化學友:
maryuen，我唸你e條問題同2004年CE chem mc差o吾多一樣:
2004 Paper II 27
Ethene can be prepared by heating ethanol with excess concentrated sulphuric acid. The reaction involved can be represented by the equation:
CH3CH2OH --> CH2=CH2 + H2O
The type of reaction involved in the preparation is
A. cracking.
B. condensation.
C. addition.
D. dehydration.
答案係D。e o個reaction有少少out of syllabus，但係你見到reaction之後ethanol(CH3CH2OH)會唔見左o個水(H2O)變成ethene，所以e o個reaction定為dehydration(脫水反應)。
通常當ethanol is heated with a dehydrating agent，例如conc. H2SO4或者Al2O3時，dehydration就會發生o架啦。
maryuen，你要留心呀e o個reaction同depolymerization一d關係都冇，depolymerization係發生o向polymer身上，而你見到e o個reaction冇polymer存在(只有ethanol)，所以一定唔係depolymerization。
回應(AL)
回應
Watson:
請問如果我想ethanal轉ethanol.可以寫NADH + H+嗎?
化學友:
Watson，雖然NADH+H+ 係可以reudce其他substance，但係考試o個時只係會o向 bio嘅respiration裡面用，考chem時係o吾接受e 隻o野o架。一般AL chem exam裡面將ethanal變成ethanol都係用下面兩個reactions:
Watson:
請問如果我想ethanal轉ethanol.可以寫NADH + H+嗎?
化學友:
Watson，雖然NADH+H+ 係可以reudce其他substance，但係考試o個時只係會o向 bio嘅respiration裡面用，考chem時係o吾接受e 隻o野o架。一般AL chem exam裡面將ethanal變成ethanol都係用下面兩個reactions:
2007年4月19日 星期四
回應(AL)
回應
02sing:
我想問下今年 syl 入面有咩係新加架?green chem 好似係..唔知點溫呀.. 點算好呀......
化學友:
02sing，你可以睇返化學友嘅第一篇文章(3月)，o個度寫左邊d係新加嘅topics，如果唔清楚，再留言比化學友丫。
02sing，好多同學仔都覺得green chem 好似讀左等於冇讀咁。其實唔使太驚o架，化學友好有信心green chem會好似下面嘅pastpaper咁，同其他topics一齊考:
1. 2003 Paper II 1c
2. 2006 Paper II 6b
仲有呀，記住下面o個12個green chem嘅 basic principles:
1. waste prevention
2. real-time analysis for pollution prevention
3. minimize the potential for accidents
4. design less hazardous chemical synthesis
5. design safer chemicals
6. design for energy efficiency
7. design for degradation
8. maximize atom economy
9. use safer solvents and auxiliaries
10. use renewable feedstocks
11. reduce derivatives
12. use catalysts
其中，8-12點最重要，一定一定要記得!!!因為考試會問你點解reaction A is better than reaction B in terms of green chemistry，通常你會用8-12點o黎做comparison。如果你冇乜時間，化學友suggest你可以睇下C C Lee 嘅green chem關於8-12嘅detail部份，唔係好多o架。不過，theory部份其實唔使睇太多，最重要係睇書裡面o個d examples，你會知道考試會點考o架喇，對你好有幫助。
最後，記住做熟atom economy嘅數，今年AL chem都幾大機會會出同埋勁易計錯o架。
02sing，加油同埋盡力呀!!!
02sing:
我想問下今年 syl 入面有咩係新加架?green chem 好似係..唔知點溫呀.. 點算好呀......
化學友:
02sing，你可以睇返化學友嘅第一篇文章(3月)，o個度寫左邊d係新加嘅topics，如果唔清楚，再留言比化學友丫。
02sing，好多同學仔都覺得green chem 好似讀左等於冇讀咁。其實唔使太驚o架，化學友好有信心green chem會好似下面嘅pastpaper咁，同其他topics一齊考:
1. 2003 Paper II 1c
2. 2006 Paper II 6b
仲有呀，記住下面o個12個green chem嘅 basic principles:
1. waste prevention
2. real-time analysis for pollution prevention
3. minimize the potential for accidents
4. design less hazardous chemical synthesis
5. design safer chemicals
6. design for energy efficiency
7. design for degradation
8. maximize atom economy
9. use safer solvents and auxiliaries
10. use renewable feedstocks
11. reduce derivatives
12. use catalysts
其中，8-12點最重要，一定一定要記得!!!因為考試會問你點解reaction A is better than reaction B in terms of green chemistry，通常你會用8-12點o黎做comparison。如果你冇乜時間，化學友suggest你可以睇下C C Lee 嘅green chem關於8-12嘅detail部份，唔係好多o架。不過，theory部份其實唔使睇太多，最重要係睇書裡面o個d examples，你會知道考試會點考o架喇，對你好有幫助。
最後，記住做熟atom economy嘅數，今年AL chem都幾大機會會出同埋勁易計錯o架。
02sing，加油同埋盡力呀!!!
回應(會考化學)
回應1
sinying:
我想問呢molecules 的3D stucture(不是指ionic struture o個d)同埋brown ring test,flavourings係唔係唔駛考架?thx
化學友:
sinying，唔使擔心呀，3D structure, brown ring test同埋flavourings全部都係out of HKCEE syllabus o架。
回應2
gladiolus:
你好,我係會考生,我想請問一d野
Which of the following is often used as a primary standard?
A.hydrochloric acid
B.oxalic acid
C.calcium hydroxide
D.sodium hydroxide
Why?
化學友:
答案係B 呀。gladiolus，可以做primary standard嘅chemical一定要
1. stable in air (唔容易decompose同埋唔會同空氣有化學反應。)
2. non-volatile (如果隻chemical volatile(揮發性)，咁佢嘅solution嘅concentration會慢慢跌。)
3. 唔吸moisture in air(空氣裡面嘅水)(吸左d水，重量會多左，咁measure嘅weight就唔準)
4. 好pure
仲有其他criteria o架，不過上面o個d係最重要嘅。citric acid fulfil 到上面嘅條件，所以可以做primary standard。
NaOH唔得，因為佢會吸moisture in air同埋react with CO2 in air (2NaOH + CO2 --> Na2CO3 + H2O)
Ca(OH)2唔得，有好多原因，其中一個同NaOH一樣，佢會react with CO2 in air (Ca(OH)2 + CO2 --> CaCO3 + H2O)
HCl(aq)唔得，因為HCl volatile。
明白嗎gladiolus?
sinying:
我想問呢molecules 的3D stucture(不是指ionic struture o個d)同埋brown ring test,flavourings係唔係唔駛考架?thx
化學友:
sinying，唔使擔心呀，3D structure, brown ring test同埋flavourings全部都係out of HKCEE syllabus o架。
回應2
gladiolus:
你好,我係會考生,我想請問一d野
Which of the following is often used as a primary standard?
A.hydrochloric acid
B.oxalic acid
C.calcium hydroxide
D.sodium hydroxide
Why?
化學友:
答案係B 呀。gladiolus，可以做primary standard嘅chemical一定要
1. stable in air (唔容易decompose同埋唔會同空氣有化學反應。)
2. non-volatile (如果隻chemical volatile(揮發性)，咁佢嘅solution嘅concentration會慢慢跌。)
3. 唔吸moisture in air(空氣裡面嘅水)(吸左d水，重量會多左，咁measure嘅weight就唔準)
4. 好pure
仲有其他criteria o架，不過上面o個d係最重要嘅。citric acid fulfil 到上面嘅條件，所以可以做primary standard。
NaOH唔得，因為佢會吸moisture in air同埋react with CO2 in air (2NaOH + CO2 --> Na2CO3 + H2O)
Ca(OH)2唔得，有好多原因，其中一個同NaOH一樣，佢會react with CO2 in air (Ca(OH)2 + CO2 --> CaCO3 + H2O)
HCl(aq)唔得，因為HCl volatile。
明白嗎gladiolus?
2007年4月18日 星期三
回應(AL)
回應
hahayi:
1.咩係methylating agent?
2.如果問題比左個concentration of reactant remain 同埋time of reaction ge表你,係咪一定要試晒order 0,1,2 先可以找到個答案出黎..我次次做都徙了很多時間..
3.幾時用back titration?
4.岩岩AL果題呢,點解CaCl2唔可以用黎dry solution of C6H5COOH?係咪同Cl會replace OH 有關?
化學友:
1. hahayi，methylating agent即係一隻chemical，佢好容易加個 methyl group (CH3)到其他compound身上。 o向AL chem exam CH3X (X= Cl, Br and I)係一隻出名嘅methylating agent。Through SN reaction (nucleophilic substitution)，個methyl group好容易加到其他compound上。例如:
RO- + CH3I --> ROCH3 + I-
alkoxide methyl group
ion is added to alkoxide ion
2. 你唔使太擔心呀，大部份AL exam題目都會明示、暗示叫你draw邊種graph o架。睇o下下面嘅例子:
2006 Paper II 3a (ii)
An experiment is conducted, at 293 K, to study the kinetics of the decomposition of H2O2(aq) in the presence of peroxidase, an enzyme.
2H2O2(aq) --> 2H2O(l) + O2(g)
By plotting a suitable graph, show that the decomposition is first order with respect to H2O2(aq). Hence, calculate the rate constant at 293 K.
2003 Paper II 3a (ii)
An experiment was carried out at 298 K to study the acid-catalysed hydrolysis of sucrose:
C12H22O11(aq) + H2O(l) --> C6H12O6(aq) + C6H12O6(aq)
By plotting a suitable graph, show that the hydrolysis is first order with respect to sucrose.
不過，如果條題目真係冇寫清楚 (好似2004 Paper II 3a(ii))，咁就可能要plot多過一個graph。但係化學友發覺通常plot 1st order就已經係答案。所以你可以plot ln[reactant] aganist time先，如果係直線就唔使plot其他graph啦。
2004 Paper II 3a (ii)
The decomposition of dinitrogen pentoxide in tetrachloromethane can be represented by the following equation:
2N2O5(in CCl4) --> 4NO2(in CCl4) + O2(g)
The table below lists the results obtained in an experiment to study the kinetics of the decomposition of dinitrogen pentoxide at 318 K.
By plotting a suitable graph, determine the rate equation for the decomposition, and hence the rate constant at 318 K.(o個 graph係1st order呀)
3. 考試時通常都唔使你自己用或者describe back titration o架。如果真係考back titration，條題目會清楚寫出o黎，你o吾使worry ar。
4. 化學友覺得唔係啦，因為alkanoic acid同chloride ion係有化學反應o個喎。
hahayi，如果仲有唔明嘅，留言比化學友丫。
hahayi:
1.咩係methylating agent?
2.如果問題比左個concentration of reactant remain 同埋time of reaction ge表你,係咪一定要試晒order 0,1,2 先可以找到個答案出黎..我次次做都徙了很多時間..
3.幾時用back titration?
4.岩岩AL果題呢,點解CaCl2唔可以用黎dry solution of C6H5COOH?係咪同Cl會replace OH 有關?
化學友:
1. hahayi，methylating agent即係一隻chemical，佢好容易加個 methyl group (CH3)到其他compound身上。 o向AL chem exam CH3X (X= Cl, Br and I)係一隻出名嘅methylating agent。Through SN reaction (nucleophilic substitution)，個methyl group好容易加到其他compound上。例如:
RO- + CH3I --> ROCH3 + I-
alkoxide methyl group
ion is added to alkoxide ion
2. 你唔使太擔心呀，大部份AL exam題目都會明示、暗示叫你draw邊種graph o架。睇o下下面嘅例子:
2006 Paper II 3a (ii)
An experiment is conducted, at 293 K, to study the kinetics of the decomposition of H2O2(aq) in the presence of peroxidase, an enzyme.
2H2O2(aq) --> 2H2O(l) + O2(g)
By plotting a suitable graph, show that the decomposition is first order with respect to H2O2(aq). Hence, calculate the rate constant at 293 K.
2003 Paper II 3a (ii)
An experiment was carried out at 298 K to study the acid-catalysed hydrolysis of sucrose:
C12H22O11(aq) + H2O(l) --> C6H12O6(aq) + C6H12O6(aq)
By plotting a suitable graph, show that the hydrolysis is first order with respect to sucrose.
不過，如果條題目真係冇寫清楚 (好似2004 Paper II 3a(ii))，咁就可能要plot多過一個graph。但係化學友發覺通常plot 1st order就已經係答案。所以你可以plot ln[reactant] aganist time先，如果係直線就唔使plot其他graph啦。
2004 Paper II 3a (ii)
The decomposition of dinitrogen pentoxide in tetrachloromethane can be represented by the following equation:
2N2O5(in CCl4) --> 4NO2(in CCl4) + O2(g)
The table below lists the results obtained in an experiment to study the kinetics of the decomposition of dinitrogen pentoxide at 318 K.
By plotting a suitable graph, determine the rate equation for the decomposition, and hence the rate constant at 318 K.(o個 graph係1st order呀)
3. 考試時通常都唔使你自己用或者describe back titration o架。如果真係考back titration，條題目會清楚寫出o黎，你o吾使worry ar。
4. 化學友覺得唔係啦，因為alkanoic acid同chloride ion係有化學反應o個喎。
hahayi，如果仲有唔明嘅，留言比化學友丫。
回應(會考化學)
回應 1
Maryuen:
謝謝化學友的解釋..^^對於這條..我又有一些問題 dil.HNO3和conc. HNO3 + CaCO3是不是仍然會出NO and NO2??其他dil. and conc. acid都會出CO2??conc. H2SO4會出SO2??
化學友:
maryuen，今日答住你部份問題先丫。化學友唸你對conc./dil. HCl, HNO3同埋H2SO4有d混亂，你睇o下下面嘅equations，可能你會clear d:
- metal + dil./conc. HCl --> salt + H2
metal oxide/metal hydroxide + dil./conc.HCl --> salt + H2O
metal carbonate + dil./conc. HCl --> salt + CO2 + H2O
- metal + dil. H2SO4 --> salt + H2
metal + conc. H2SO4 --> salt + SO2 + H2O
metal oxide/metal hydroxide + dil./conc.H2SO4 --> salt + H2O
metal carbonate + dil./conc.H2SO4 --> salt + CO2 + H2O
- metal + very dil. HNO3--> salt + H2
metal + dil. HNO3--> salt + NO + H2O
metal + conc. HNO3 --> salt + NO2 + H2O
metal oxide/metal hydroxide + very dil./dil./conc.HNO3 --> salt + H2O
metal carbonate + very dil./dil./conc.HNO3 --> salt + CO2 + H2O
留意bolded左 嘅equations，睇下幫唔幫到你。
回應 2
Maryuen:
1. maryuen的past paper有問題了..這次是2002..6aii怎麼知道H2O formed is in gaseous state?
2. 有關於electronic diagram..for example..CO2嗯..如果我所有的electrons(both C and O)是用cross的話,ok嗎??
化學友:
1. heat一隻substance通常都唔會太低溫(一般都有百幾2百度)，所以通常H2O exist as a gas。不過化學友記得當時嘅marking接受H2O係(g)或者(l)。
2. OK o架，會考嘅electronic diagram只畫dot或者cross都得。
Maryuen，你都好努力鋤pastpaper wor，繼續add oil啦。
Maryuen:
謝謝化學友的解釋..^^對於這條..我又有一些問題 dil.HNO3和conc. HNO3 + CaCO3是不是仍然會出NO and NO2??其他dil. and conc. acid都會出CO2??conc. H2SO4會出SO2??
化學友:
maryuen，今日答住你部份問題先丫。化學友唸你對conc./dil. HCl, HNO3同埋H2SO4有d混亂，你睇o下下面嘅equations，可能你會clear d:
- metal + dil./conc. HCl --> salt + H2
metal oxide/metal hydroxide + dil./conc.HCl --> salt + H2O
metal carbonate + dil./conc. HCl --> salt + CO2 + H2O
- metal + dil. H2SO4 --> salt + H2
metal + conc. H2SO4 --> salt + SO2 + H2O
metal oxide/metal hydroxide + dil./conc.H2SO4 --> salt + H2O
metal carbonate + dil./conc.H2SO4 --> salt + CO2 + H2O
- metal + very dil. HNO3--> salt + H2
metal + dil. HNO3--> salt + NO + H2O
metal + conc. HNO3 --> salt + NO2 + H2O
metal oxide/metal hydroxide + very dil./dil./conc.HNO3 --> salt + H2O
metal carbonate + very dil./dil./conc.HNO3 --> salt + CO2 + H2O
留意bolded左 嘅equations，睇下幫唔幫到你。
回應 2
Maryuen:
1. maryuen的past paper有問題了..這次是2002..6aii怎麼知道H2O formed is in gaseous state?
2. 有關於electronic diagram..for example..CO2嗯..如果我所有的electrons(both C and O)是用cross的話,ok嗎??
化學友:
1. heat一隻substance通常都唔會太低溫(一般都有百幾2百度)，所以通常H2O exist as a gas。不過化學友記得當時嘅marking接受H2O係(g)或者(l)。
2. OK o架，會考嘅electronic diagram只畫dot或者cross都得。
Maryuen，你都好努力鋤pastpaper wor，繼續add oil啦。
2007年4月17日 星期二
會考化學(6)
今次化學友要同同學仔講嘅topic係detergent(清潔劑)。e個topic o向 CE chem通常分為兩部份，就係preparation of soap(肥皂製備)同埋soapy(皂性)和soapless detergent(非皂性清潔)嘅比較。e個topic其實真係幾大路o架。
1. Preparation of soap(肥皂製備)
- 將oil(油)或者fat(脂肪)同埋NaOH加熱及不時攪吓佢直至兩層layers合而為一。(oil同埋NaOH本來immiscible，但係product就solulbe in water，所以two layers become one layer)
- 然後熄火，加入brine (濃鹽水)，就有d white solid(白色固體)出咗黎。(o個過程叫salting out。)
- 然後再用filtration(過濾)同埋用d distilled water洗吓d solid就得la。
(bold左嘅地方係會考嘅重要字眼o黎o架，同學仔一定要記住呀。)
2. 比較soapy(皂性)和soapless detergent(非皂性清潔)
相似:
(i) 大家都係係soft water(軟水)裡頭work嘅。
(ii) Soap 同埋 straight-chain soapless detergent(含直鍊的非皂性清潔)都係biodegradable(生物可降解)。
相異:
(i) 只有Soapless detergent係 hard water(硬水)同埋acidic solution(酸性液體)裡頭work嘅。而soap係hard water裡面就形成scum (浮渣)而o向acidic solution裡面就形成precipitate。
(ii) Branch-chain soapless detergent (含支鍊的非皂性清潔)係non-biodegradable。
1. Preparation of soap(肥皂製備)
- 將oil(油)或者fat(脂肪)同埋NaOH加熱及不時攪吓佢直至兩層layers合而為一。(oil同埋NaOH本來immiscible，但係product就solulbe in water，所以two layers become one layer)
- 然後熄火，加入brine (濃鹽水)，就有d white solid(白色固體)出咗黎。(o個過程叫salting out。)
- 然後再用filtration(過濾)同埋用d distilled water洗吓d solid就得la。
(bold左嘅地方係會考嘅重要字眼o黎o架，同學仔一定要記住呀。)
2. 比較soapy(皂性)和soapless detergent(非皂性清潔)
相似:
(i) 大家都係係soft water(軟水)裡頭work嘅。
(ii) Soap 同埋 straight-chain soapless detergent(含直鍊的非皂性清潔)都係biodegradable(生物可降解)。
相異:
(i) 只有Soapless detergent係 hard water(硬水)同埋acidic solution(酸性液體)裡頭work嘅。而soap係hard water裡面就形成scum (浮渣)而o向acidic solution裡面就形成precipitate。
(ii) Branch-chain soapless detergent (含支鍊的非皂性清潔)係non-biodegradable。
同學仔睇o下下面o個table對你有冇幫助丫:
仲有呀，記住讀埋how soap removes dirt on a cloth。
同之前一樣，讀熟完之後記住做下面e幾條paspaper呀，好有用o架:
1. 1995 PaperI 9a
2. 2004 Paper I 7b (包括左how soap removes dirt on a cloth嘅solution)
3. 有時間做埋1994 Paper I 5a
2007年4月16日 星期一
回應(會考化學)
Sampson:
首先唔該你解答左我上次既問題先但係我想問下ｅ條....
48
1st statement: Carbon dioxide can effectively be prepared by the action of dilute sulphuric acid on calcium carbonate.
2nd statment: Carbonates react with dilute acids to give carbon dioxide.
你解釋好似有d問題咁..答案係c ...但係應該係 1st statement錯因為c 係話 1st statement錯 2nd 岩..仲有..1st statement..係 dil. H2SO4 + CaCO3...而唔係 metal + dil. HNO3其實...1st statement 錯既 reason係唔係..."effectively" e個字呢因為..H2SO4 + CaCO3 -> CaSO4 + H2O + CO2但係唔係...好 effectively..??其實我都唔知我岩唔岩 化學友 你點睇??
化學友:
唔該晒阿sampson，手快快將個'o岩'字寫成'錯'字tim,thanks ah。 (e 家改返啦。)
不過可能化學友寫得簡單左d令你誤會左2nd statement。其實，化學友發覺好多同學仔一到考試就會唔小心咁以為metals、oxide、hydroxide或者carbonate + conc.H2SO4會出SO2，而如果加dil. HNO3就會出NO。因為2nd statement係話dil. acid,maryeun就覺得dil.HNO3+carbonate應該出NO唔係CO2，所以佢認為2nd statement都係錯嘅。
至於1st statement，你條equation係o岩o架，而因為CaSO4 formed係solid，佢會coats on the surface of CaCO3(s)，阻止H2SO4接觸CaCO3(s)。所以reaction will stop soon，而得好少CO2收集到。就因為咁，o個方法唔effective去prepare CO2。明白嗎sampson。
首先唔該你解答左我上次既問題先但係我想問下ｅ條....
48
1st statement: Carbon dioxide can effectively be prepared by the action of dilute sulphuric acid on calcium carbonate.
2nd statment: Carbonates react with dilute acids to give carbon dioxide.
你解釋好似有d問題咁..答案係c ...但係應該係 1st statement錯因為c 係話 1st statement錯 2nd 岩..仲有..1st statement..係 dil. H2SO4 + CaCO3...而唔係 metal + dil. HNO3其實...1st statement 錯既 reason係唔係..."effectively" e個字呢因為..H2SO4 + CaCO3 -> CaSO4 + H2O + CO2但係唔係...好 effectively..??其實我都唔知我岩唔岩 化學友 你點睇??
化學友:
唔該晒阿sampson，手快快將個'o岩'字寫成'錯'字tim,thanks ah。 (e 家改返啦。)
不過可能化學友寫得簡單左d令你誤會左2nd statement。其實，化學友發覺好多同學仔一到考試就會唔小心咁以為metals、oxide、hydroxide或者carbonate + conc.H2SO4會出SO2，而如果加dil. HNO3就會出NO。因為2nd statement係話dil. acid,maryeun就覺得dil.HNO3+carbonate應該出NO唔係CO2，所以佢認為2nd statement都係錯嘅。
至於1st statement，你條equation係o岩o架，而因為CaSO4 formed係solid，佢會coats on the surface of CaCO3(s)，阻止H2SO4接觸CaCO3(s)。所以reaction will stop soon，而得好少CO2收集到。就因為咁，o個方法唔effective去prepare CO2。明白嗎sampson。
回應(會考化學)
回應
Maryuen:
你好,化學友..我是maryuen我又找到新的問題想請教你我想問chem 2006的past paper的mc
4(可以explain一下嗎?)
9(why it is low melting point?容易melt好嗎??那high elecrical conductivity不是更重要嗎?)
16(可以explain一下嗎?)
48(那個2nd statement的dilute acids not include dilute nitric acid??)
唔..我還想知道那個NH4+會不會是一個oxidizing agent if not in zinc-carbon cell??
對不起..我還想知道在什麼時候,一些reaction,heat would be liberated..即什麼時候是exothermic, 什麼時候是endothermic??
化學友:
4.
Which of the following combinations concerning the change of physical state of a substance is INCORRECT?
Change of physical state Process
A. liquid to gas evaporation
B. liquid to solid precipitation
C. solid to gas sublimation
D. gas to liquid condensation
B錯呀，因為一隻物質由liquid變成solid係叫做freezing。precipitation係形容chemical reaction當中有d唔溶嘅solid形成左,e.g. Fe2+(aq) + 2OH-(aq) --> Fe(OH)2(s)
9.
Which of the following properties is considered the most important one when choosing an alloy for making fuse in electric plugs?
A. low melting point
B. high electrical conductivity
C. good ductility
D. high mechanical strength
答案係B。fuse嘅作用係當electric plugs嘅current太大時斷左o個circuit，減少意外。一般o黎講current大會令到溫度高左，所以如果fuse嘅melting point低，fuse就會溶，咁樣circuit就會斷左。
16
Which of the following compounds is formed from the reaction of propene with chlorine
好Q呀，上個禮拜化學友有d學生都問左e條。maryuen，做e條最緊要將條reaction寫出o黎，睇下面:
答案係B。o拿，如果你睇返個reaction，A同埋D都錯，因為2個Cl唔會o向同一個carbon上面。而C都錩，因為2個Cl應該o向1,2位，而唔係o向1,3位。
個表差唔多包晒會考常考嘅reactions, 你睇下幫o吾幫到你丫。
Maryuen:
你好,化學友..我是maryuen我又找到新的問題想請教你我想問chem 2006的past paper的mc
4(可以explain一下嗎?)
9(why it is low melting point?容易melt好嗎??那high elecrical conductivity不是更重要嗎?)
16(可以explain一下嗎?)
48(那個2nd statement的dilute acids not include dilute nitric acid??)
唔..我還想知道那個NH4+會不會是一個oxidizing agent if not in zinc-carbon cell??
對不起..我還想知道在什麼時候,一些reaction,heat would be liberated..即什麼時候是exothermic, 什麼時候是endothermic??
化學友:
4.
Which of the following combinations concerning the change of physical state of a substance is INCORRECT?
Change of physical state Process
A. liquid to gas evaporation
B. liquid to solid precipitation
C. solid to gas sublimation
D. gas to liquid condensation
B錯呀，因為一隻物質由liquid變成solid係叫做freezing。precipitation係形容chemical reaction當中有d唔溶嘅solid形成左,e.g. Fe2+(aq) + 2OH-(aq) --> Fe(OH)2(s)
9.
Which of the following properties is considered the most important one when choosing an alloy for making fuse in electric plugs?
A. low melting point
B. high electrical conductivity
C. good ductility
D. high mechanical strength
答案係B。fuse嘅作用係當electric plugs嘅current太大時斷左o個circuit，減少意外。一般o黎講current大會令到溫度高左，所以如果fuse嘅melting point低，fuse就會溶，咁樣circuit就會斷左。
16
Which of the following compounds is formed from the reaction of propene with chlorine
好Q呀，上個禮拜化學友有d學生都問左e條。maryuen，做e條最緊要將條reaction寫出o黎，睇下面:
答案係B。o拿，如果你睇返個reaction，A同埋D都錯，因為2個Cl唔會o向同一個carbon上面。而C都錩，因為2個Cl應該o向1,2位，而唔係o向1,3位。
48
1st statement: Carbon dioxide can effectively be prepared by the action of dilute sulphuric acid on calcium carbonate.
2nd statment: Carbonates react with dilute acids to give carbon dioxide.
答案係C。2nd statemento岩o架。又咁Q，化學友o個幾個學生又有問e條。maryuen，我唸你記錯左lu, metal + dil. HNO3先會出NO，carbonate + very dil. HNO3、dil.HNO3或者conc. HNO3都係出CO2 o架。
至於NH4+裡面個N好少oxidize其他o野，因為佢個O.N.已經-3(好低)，O.N.好難再decrease。至於H就可以oxidize其他o野，O.N.會由+1 decrease to 0(H+ --> H2)。不過呢化學友覺得CE chem好少會咁問。
最後，邊d reactions係exothermic邊d係endothermic，好難generalize wor。 不過，o向CE chem level大至可以將d reactions咁分類:
個表差唔多包晒會考常考嘅reactions, 你睇下幫o吾幫到你丫。
回應(AL)
回應1
Or:
i want to know why to use P2O5for drying a moist sample of C2H5COOH?THX~
化學友:
Or,化學友覺得你條問題同 AL 2003 Paper I 8 一樣o架:
The following compounds can be used as drying agents:
Na2SO4(s), NaOH(s), CaCl2(s) and P2O5(s)
Choose, from the above, one compound which is most suitable and effective
for drying a moist solid sample of C6H5CO2H.
NaOH 就一定唔得啦，因為acid (C6H5CO2H)同alkali(NaOH)有reaction。化學友都check過書，P2O5真係standard嘅drying agent for C6H5CO2H，但係就冇講why Na2SO4 and CaCl2 cannot。至於街外嘅solution guide嘅解釋又似乎有好多漏洞。(化學友有時唸會唔會Na2SO4 同CaCl2 用於C6H5CO2H嘅drying power唔係太好呢?)
街賣嘅pastpaper嘅answer係話P2O5，但據化學友所知當時嘅AL exam係接受下面三個答案:
P2O5(s) / Na2SO4(s) / CaCl2(s)
各位如果知explanation嘅話，留言比我丫。
Or:
i want to know why to use P2O5for drying a moist sample of C2H5COOH?THX~
化學友:
Or,化學友覺得你條問題同 AL 2003 Paper I 8 一樣o架:
The following compounds can be used as drying agents:
Na2SO4(s), NaOH(s), CaCl2(s) and P2O5(s)
Choose, from the above, one compound which is most suitable and effective
for drying a moist solid sample of C6H5CO2H.
NaOH 就一定唔得啦，因為acid (C6H5CO2H)同alkali(NaOH)有reaction。化學友都check過書，P2O5真係standard嘅drying agent for C6H5CO2H，但係就冇講why Na2SO4 and CaCl2 cannot。至於街外嘅solution guide嘅解釋又似乎有好多漏洞。(化學友有時唸會唔會Na2SO4 同CaCl2 用於C6H5CO2H嘅drying power唔係太好呢?)
街賣嘅pastpaper嘅answer係話P2O5，但據化學友所知當時嘅AL exam係接受下面三個答案:
P2O5(s) / Na2SO4(s) / CaCl2(s)
各位如果知explanation嘅話，留言比我丫。
2007年4月15日 星期日
回應(會考化學)
回應1
sampson:
你好!想問下你 正極 幾時係陽極 幾時係陰極o係唔o係 係電池個陣 正極 係 陰極但係係 電解個陣 正極 就係 陽極ar?
化學友:
sampson, 你講得o岩呀。不過化學友都post o個表比你，睇下對你有冇用(雖然可能你已經識):
Red cat (reduction at cathode)
An ox (oxidation at anode)
sampson，答到你問題嗎?
回應2
maryuen:
其實我已經在yahoo問過東西了..http://hk.knowledge.yahoo.com/question/?qid=7007041205645可是我是不太明白..我想問2005 8b 有英文的explanation嗎??x is not a mixture的解釋..> <(2005 8b: X is known to be a mixed oxide composed of PbO and PbO2. Based on your answer in (a), deduce the mole ratio of PbO to PbO2 in X.) 還有...我想知道是不是all the metals in the same group of the periodic table have their melting point decrease aown the group??
化學友:
問題1
maryuen，下面係2005 Paper I 8b嘅答案:
X is a mixture of PbO and PbO2 in a mole ratio of 2 : 1.
or,
X is not a mixture. In X, two-third of the lead exists in an oxidation number +2, while one-third in an oxidation number +4.
我唸你o吾明 ‘or’ 嘅答案。因為CE marking有時會寬鬆d，所以就算條題目話明X係mixture，但係你寫答案時話X唔係mixture，CE都接受。不過，你要寫明Pb3O4 係一隻compound(唔係mixture)，而e隻compound裡面嘅Pb有兩種oxidation number(+2同埋+4)，兩種Pb嘅比例係2:1。(其實化學友覺得CE冇理由接’受or’ 嘅答案，對同學仔係好misleading。化學友好多學生都問我e條，化學友每次都叫佢地唔好理’or’ 嘅答案。)
問題2
Yes. In general, melting point of metals decreases down the group. 原因係 the size of metals get larger when moving down the group。Hence, the attraction between positive charged metal ions and delocalized electrons gets weaker.
maryuen其實e樣o野好易記o架:reactivity of metals increases down the group而reactivity of halogens decreases down the group。類似咁樣，m.p. of metals decreases down the group而m.p.of halogens increases down the group.明白嗎?
sampson:
你好!想問下你 正極 幾時係陽極 幾時係陰極o係唔o係 係電池個陣 正極 係 陰極但係係 電解個陣 正極 就係 陽極ar?
化學友:
sampson, 你講得o岩呀。不過化學友都post o個表比你，睇下對你有冇用(雖然可能你已經識):
Red cat (reduction at cathode)
An ox (oxidation at anode)
sampson，答到你問題嗎?
回應2
maryuen:
其實我已經在yahoo問過東西了..http://hk.knowledge.yahoo.com/question/?qid=7007041205645可是我是不太明白..我想問2005 8b 有英文的explanation嗎??x is not a mixture的解釋..> <(2005 8b: X is known to be a mixed oxide composed of PbO and PbO2. Based on your answer in (a), deduce the mole ratio of PbO to PbO2 in X.) 還有...我想知道是不是all the metals in the same group of the periodic table have their melting point decrease aown the group??
化學友:
問題1
maryuen，下面係2005 Paper I 8b嘅答案:
X is a mixture of PbO and PbO2 in a mole ratio of 2 : 1.
or,
X is not a mixture. In X, two-third of the lead exists in an oxidation number +2, while one-third in an oxidation number +4.
我唸你o吾明 ‘or’ 嘅答案。因為CE marking有時會寬鬆d，所以就算條題目話明X係mixture，但係你寫答案時話X唔係mixture，CE都接受。不過，你要寫明Pb3O4 係一隻compound(唔係mixture)，而e隻compound裡面嘅Pb有兩種oxidation number(+2同埋+4)，兩種Pb嘅比例係2:1。(其實化學友覺得CE冇理由接’受or’ 嘅答案，對同學仔係好misleading。化學友好多學生都問我e條，化學友每次都叫佢地唔好理’or’ 嘅答案。)
問題2
Yes. In general, melting point of metals decreases down the group. 原因係 the size of metals get larger when moving down the group。Hence, the attraction between positive charged metal ions and delocalized electrons gets weaker.
maryuen其實e樣o野好易記o架:reactivity of metals increases down the group而reactivity of halogens decreases down the group。類似咁樣，m.p. of metals decreases down the group而m.p.of halogens increases down the group.明白嗎?
會考化學(5)
今次化學友想同同學仔講嘅係corrosion of aluminium (鋁的腐蝕) 同埋anodization (陽極氧化)。呢個topic雖然好少出長題目，但有d重點都要留意吓。
鋁嘅抗腐蝕好過鐵因為aluminium oxide(氧化鋁)會穩固咁依附o向aluminium嘅表面，同埋impermeable to oxygen and water。而rust(鐵鏽)嘅結構就loose d啦，容易d fall off同埋permeable to oxygen and water。
要再加強鋁嘅抗腐蝕性(corrosion resistance)就要靠anodization (陽極氧化)。方法主要係靠電解dil. sulphuric acid (稀硫酸) o黎產生oxygen(氧) 而產生嘅氧就可同o向anode嘅aluminium反應變成aluminium oxide。所以aluminium oxide嘅厚度同埋抗腐蝕性就會增加。
除左加強鋁嘅抗腐蝕性外，anodized aluminium仲可以染上其他顏色添。
但係有三點同學仔係成日錯o架，一定要留意:
1. o向會考anodization e o個名稱係用o向aluminium only唔會用o向其他metals身上。所以冇anodization of iron。
2. Anodization增加corrosion resistance of aluminium唔係增加resistance to rusting 。 Rusting e o個term只係專用o向iron身上。
3. Anodization 增加corrosion resistance of aluminium唔會增加strength of aluminium。
鋁嘅抗腐蝕好過鐵因為aluminium oxide(氧化鋁)會穩固咁依附o向aluminium嘅表面，同埋impermeable to oxygen and water。而rust(鐵鏽)嘅結構就loose d啦，容易d fall off同埋permeable to oxygen and water。
要再加強鋁嘅抗腐蝕性(corrosion resistance)就要靠anodization (陽極氧化)。方法主要係靠電解dil. sulphuric acid (稀硫酸) o黎產生oxygen(氧) 而產生嘅氧就可同o向anode嘅aluminium反應變成aluminium oxide。所以aluminium oxide嘅厚度同埋抗腐蝕性就會增加。
除左加強鋁嘅抗腐蝕性外，anodized aluminium仲可以染上其他顏色添。
但係有三點同學仔係成日錯o架，一定要留意:
1. o向會考anodization e o個名稱係用o向aluminium only唔會用o向其他metals身上。所以冇anodization of iron。
2. Anodization增加corrosion resistance of aluminium唔係增加resistance to rusting 。 Rusting e o個term只係專用o向iron身上。
3. Anodization 增加corrosion resistance of aluminium唔會增加strength of aluminium。
2007年4月14日 星期六
回應(會考化學)
回應1
sinying:
真係唔該哂,你個表好有用,我立即抄低了!但係呢,我揾到一條ce mc:
26.On heating, blue copper(II) sulphate crystals gradually change to a white powder. Which of the following statements are correct?
(1)Heat would be liberated if water is added to the white powder.
(2)On further heating, the white powder would turn reddish-brown.
(3)chemical change occurs during the heating of the blue crystals.
A. (1) and (2) only
B. (1) and (3) only
C. (2) and (3) only
D. (1), (2) and (3)
answer話copper(II) sulphate唔會decomposition,我想問依d compond 係唔係要死記或者好冇方法記架?再一次唔該哂!!
化學友:
sinying，可能化學友上一個嘅回覆唔係太清楚，所以o向e度再講多d丫。
當blue copper(II) sulphate crystal遇熱之後water of crystallization就會放出，剩返white copper(II) sulphate (e.g. CuSO4.5H2O --> CuSO4 + 5H2O)。因為CE只係假設我地知道carbonate, hydrogencarbonate, hydroxide同埋oxide會遇熱分解，所以如果CE問其他ionic compounds會唔會decompose under high temperature，正常o黎講就會當冇decomposition o架啦。所以NaCl, PbCl2, CuSO4或其他ionic compounds都唔會decompose。如果CE條問題要考一隻會decompose嘅ionic compound，佢一定會清楚話比你聽隻compound會decompose。簡單o黎講，當冇特別指示時，我地可以當所有其他ionic compounds遇熱都唔會decompose。所以化學友覺得唔使死記o架。
sinying，唔知答唔答到你嘅問題呢?如果唔得，你再留言丫，化學友再試下再答過啦。
回應2
eddy:
化學友我想問你關於chem個d colour.好似I2咁,係organic solvent係 purple,係佢gas state都係purple.重有無其他係有唔同colour係唔同state加.重有我想問sulphur,bromine,ammonia個d係room temperature係咩colour同邊d係denser than air...唔該哂!!!
化學友:
eddy，o向CE level o黎講剩係得I2會咁樣，其他o野唔會。 至於佢地嘅colour:
sulphur係yellow(好易記o架sulphur係硫磺所以黃色lor。)
bromine係orange
ammonia係colorless
一般o黎講solid同埋liquid嘅density一定高過gas。因為o向室溫sulphur係solid而bromine係liquid，所以sulphur同捚bromine嘅density高過air。
如果兩隻substances都係gas，邊一隻substance嘅relative molecular mass大d，o個一隻substance就有大d嘅density。 NH3嘅relative molecular mass = 14 + 1 x 3 = 17 而air嘅relative molecular mass大約=28x0.8+32x0.2 = 29 (28係N2嘅rleative molecular mass而32係O2嘅relative molecular mass;0.8同埋0.2係佢地o向空氣裡面各自嘅比例。)，所以NH3嘅denisty低過air。明白嗎eddy?
sinying:
真係唔該哂,你個表好有用,我立即抄低了!但係呢,我揾到一條ce mc:
26.On heating, blue copper(II) sulphate crystals gradually change to a white powder. Which of the following statements are correct?
(1)Heat would be liberated if water is added to the white powder.
(2)On further heating, the white powder would turn reddish-brown.
(3)chemical change occurs during the heating of the blue crystals.
A. (1) and (2) only
B. (1) and (3) only
C. (2) and (3) only
D. (1), (2) and (3)
answer話copper(II) sulphate唔會decomposition,我想問依d compond 係唔係要死記或者好冇方法記架?再一次唔該哂!!
化學友:
sinying，可能化學友上一個嘅回覆唔係太清楚，所以o向e度再講多d丫。
當blue copper(II) sulphate crystal遇熱之後water of crystallization就會放出，剩返white copper(II) sulphate (e.g. CuSO4.5H2O --> CuSO4 + 5H2O)。因為CE只係假設我地知道carbonate, hydrogencarbonate, hydroxide同埋oxide會遇熱分解，所以如果CE問其他ionic compounds會唔會decompose under high temperature，正常o黎講就會當冇decomposition o架啦。所以NaCl, PbCl2, CuSO4或其他ionic compounds都唔會decompose。如果CE條問題要考一隻會decompose嘅ionic compound，佢一定會清楚話比你聽隻compound會decompose。簡單o黎講，當冇特別指示時，我地可以當所有其他ionic compounds遇熱都唔會decompose。所以化學友覺得唔使死記o架。
sinying，唔知答唔答到你嘅問題呢?如果唔得，你再留言丫，化學友再試下再答過啦。
回應2
eddy:
化學友我想問你關於chem個d colour.好似I2咁,係organic solvent係 purple,係佢gas state都係purple.重有無其他係有唔同colour係唔同state加.重有我想問sulphur,bromine,ammonia個d係room temperature係咩colour同邊d係denser than air...唔該哂!!!
化學友:
eddy，o向CE level o黎講剩係得I2會咁樣，其他o野唔會。 至於佢地嘅colour:
sulphur係yellow(好易記o架sulphur係硫磺所以黃色lor。)
bromine係orange
ammonia係colorless
一般o黎講solid同埋liquid嘅density一定高過gas。因為o向室溫sulphur係solid而bromine係liquid，所以sulphur同捚bromine嘅density高過air。
如果兩隻substances都係gas，邊一隻substance嘅relative molecular mass大d，o個一隻substance就有大d嘅density。 NH3嘅relative molecular mass = 14 + 1 x 3 = 17 而air嘅relative molecular mass大約=28x0.8+32x0.2 = 29 (28係N2嘅rleative molecular mass而32係O2嘅relative molecular mass;0.8同埋0.2係佢地o向空氣裡面各自嘅比例。)，所以NH3嘅denisty低過air。明白嗎eddy?
2007年4月12日 星期四
回應(會考化學)
回應 1
hi:
化學友,你個board 好正有好多好好用的資料,多謝你!我想問呢silver同gold係唔係唔會同conc.nitric acid 有reaction?? thx
化學友:
阿hi，多謝你嘅鼓勵呀。
答返你條問題先。o向CE level o黎講，所有o向reactivity series嘅metals都會同conc. nitric acid react除左platinum同埋gold。所以silver會同conc. nitric acid react而gold就唔會。有問題可再留言比化學友丫。
回應 2
lo:
我遲D過Eng 讀書我Take左Chem但我Skip左F3 最Basic個一年Chem課我想補返佢 但正經chem課本我唔明 D英文too difficult to understand我想問下有無D用中文同較得意 易明ge chem 課外書好用呀唔該你呀 救明恩人~
化學友:
lo, 講真化學友真係搵唔到香港有出版社出本易明嘅chem課外書，不過化學友可以推介兩本台灣出嘅書俾你 ，兩本都寫得幾好o架。佢地平均兩三頁內容就介紹一個基本化學概念，如摩爾、塑膠、電解等，仲有圖畫同埋table幫助解釋。你試吓去商務、三聯書局搵吓，價錢應該100元以下。
hi:
化學友,你個board 好正有好多好好用的資料,多謝你!我想問呢silver同gold係唔係唔會同conc.nitric acid 有reaction?? thx
化學友:
阿hi，多謝你嘅鼓勵呀。
答返你條問題先。o向CE level o黎講，所有o向reactivity series嘅metals都會同conc. nitric acid react除左platinum同埋gold。所以silver會同conc. nitric acid react而gold就唔會。有問題可再留言比化學友丫。
回應 2
lo:
我遲D過Eng 讀書我Take左Chem但我Skip左F3 最Basic個一年Chem課我想補返佢 但正經chem課本我唔明 D英文too difficult to understand我想問下有無D用中文同較得意 易明ge chem 課外書好用呀唔該你呀 救明恩人~
化學友:
lo, 講真化學友真係搵唔到香港有出版社出本易明嘅chem課外書，不過化學友可以推介兩本台灣出嘅書俾你 ，兩本都寫得幾好o架。佢地平均兩三頁內容就介紹一個基本化學概念，如摩爾、塑膠、電解等，仲有圖畫同埋table幫助解釋。你試吓去商務、三聯書局搵吓，價錢應該100元以下。
圖解化學就淺d，你自已睇下鐘意邊本啦。
最後，化學友suggest你去Eng前買返本CE level嘅chem書，因為香港同Eng嘅chem有好多都幾似，買本過去守門口，有乜唔明都有reference用。你可以買本精工出版社叫chemistry for you嘅書，一套四本，中英對照，化學友覺得本書寫得幾好o架。
回應3
masiy:
請問有沒有適合中三程度的化學網頁？
化學友:
masiy,睇睇e d website對你有冇用:
Fundamental virtual chemistry texthttp://www.chem1.com/acad/webtext/virtualtextbook.html
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