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。