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:
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjnW6E_8YHYZTW-wa889Oo6FXCnDdK553n-gOs_sJ4alKw2nO_lHRj6mmF7lcWGpSwP7avC6LY3Ml6ZLFlCn9Mml0H_3U5D_RFGQGe9Ee52XwlFbQf_vTfv7eLDqNkVujQmbDmIEMcxWnI/s400/diag_Page_01.jpg)
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
4 則留言:
http://friendium.blogspot.com/2007/04/blog-post_28.html
= =...不知道你有沒有看到我的問題,可以幫幫我嗎....Q7-Q18
看不到嗎......問題太多嗎?
那可以答我一個問題嗎?
濃氫氧化鈉溶液、飽和氯化鈉溶液有甚麼分別.....因為有時製造肥皂時要用這兩種..
但飽和氯化鈉不等於濃氫氧化鈉...
電解兩種溶液都是出氯+氫嗎?
製造肥皂時用那種都行嗎
首先多謝你之前的解答,令我獲益不少
請問可否公佈今天的會考化學(二)的答案?
我想問:
salt bridge 嘅 function 唔係應該係 maintain the electrical neutrality of the solution (half-cell) 咩?
因為係ionic solution 傳電ge原理係一邊electrode做reduction 另一邊electrode做oxidation (即係一邊receive electron, 另一邊release electron.. 如果2個electrode分別插係2個solution到 (half cells), 咁一邊ge solution(e.g. cathrode果邊)一直放electron, 個charge of solution 咪 positive lo? salt bridge就係放番d anion 落去cathrode果邊個half cell果到maintain個electrical neutrality呀ma~唔係咩? 點解係allow ion 去 flow through呀?
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