6. Water (H2O) is an oxide of hydrogen. Electrolysis of water in the presence of sulphuric acid give hydrogen and oxygen in a volume ratio of 2:1.
(iv) Is it possible to deduce the formula of water from the results of electrolysis? Explain your answer.
According to the marking scheme:
Yes.
Volume of hydrogen collected: Volume of oxygen collected = 2:1
=> In water, hydrogen and oxygen combine in the ratio 2:1
As the atomicity of hydrogen and oxygen are both 2,
formula of water is H2O.
(Atomicity = Number of atoms of an element that combine together to form a molecule.
e.g. A molecule of oxygen (O2) has atomicity 2;
sulphur (S8) has atomicity 8. )
However, by the solution given by "Joint", the answer is "No" because only emprical formula can be deduced.
Which one is correct?
If marking scheme is correct, I wonder why knowing the atomicity of H and O can immediately deduce the formula of water. Please show this in details. Thank you very much.
2004 CE Chem 6(a)(iv)
2008-04-09 8:11 pm
回答 (3)
2008-04-09 9:47 pm
✔ 最佳答案
There are different type of formulae, such as molecular formulae, empirical formulae, structural formulae, etc. In the marking scheme (you quoted), it stated that the “(empirical) formula of water” can be deducted.
Vol. of hydrogen : Volume of oxygen = 2 : 1
Vol. of H2 formed : Vol. of O2 formed = 2 : 1 (since both gases are diatomic)
Mol. of H2 formed : Mol. of O2 formed = 2 : 1 (by Avogadro’s law)
Mol. of H released from water : Mol. of O release from water = 2 : 1
Mol. of H in water : Mol of O in water = 2 : 1
The empirical formula of of water = 2 : 1
The formula here is empirical formula, but not molecular formula, because it is deduced from the mole ratio of H : O. Refer to the deduction above. The atomicity of hydrogen and that of oxygen are used in the deduction of the empirical formula of water, but the conclusion is not got immediately from them.
I haven’t read “Joint”. However, I feel the solution of “Joint” (as quoted”) is so strange: “It is impossible to deduce the formula because only empirical formula can be deduced.” This may be due to the wrong concept of the author that he/she does not realize “empirical formula” as a form of “formula”.
2008-04-14 7:27 am
你想我比咩評語? 我唔想打D 「唔該晒你呀! 」之類的行貨
如果純粹推斷 emprical formula ，我本來就懂的
而且 兩粒星 = 有幫助
我不是質疑 Uncle Michael 化學的功力 (尤見他化學領域回答、採用率是何其卓越)
但我始終認為問 formula 一定要答 molecular formula
這是我的原則
即使這看起來是多麼固執和愚蠢
如果純粹推斷 emprical formula ，我本來就懂的
而且 兩粒星 = 有幫助
我不是質疑 Uncle Michael 化學的功力 (尤見他化學領域回答、採用率是何其卓越)
但我始終認為問 formula 一定要答 molecular formula
這是我的原則
即使這看起來是多麼固執和愚蠢
2008-04-13 8:27 am
答案的解釋相信花了不少時間，咁正既答案都剩係比兩粒星，仲話 no comment，發問者可謂涼薄。
綠色的答案第二、三、四行已解釋了所謂的附加問題，睇下喇！
綠色的答案第二、三、四行已解釋了所謂的附加問題，睇下喇！
收錄日期: 2021-04-13 15:24:43
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