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):

唔知你係唔係讀英文chem呢，如果係嘅話我o念下面嘅wordings你都學過同埋都可以幫到你:

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?