still got summore... -- Chemistry

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Date Posted: 05:35:58 11/04/01 Sun
Author: Jac
Subject: still got summore...

Mr yeo,
still got summore qn...
tys (10)6 no 34 u sae the ans is zinc hydroxide rite? But y leh? i thought zinc hydroxide is an alkaline so can react wif HCl? zinc carbonate and zinc metal oso can react wif acid. so y not zinc nitrate,since its a salt and can't react wif acid to form acid? -blur-
Then same page qn 28 ans is zinc carbonate rite? but it got gives out carbon dioxide as a gas when reacted wif alkali or acid anot? funny leh, it tot got
same chapter qn 40... my ans is A but ans booklet sae is B. u mean an aqueous solution of ph 1 have a low concentration of OH minus ions? i tot is dun have at all? dunno leh... like real but like not real so i dunno...
same chapter again no 64 i dunno how to do at all. can tell me? thanx

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Replies:

[> Re: still got summore... -- Mr. Yeo Woei Ter, 20:05:18 11/04/01 Sun

Hi Jac!

I think I have already answered you thru' e-mail. But here's the same thing again!

In page (10)6, the mistakes I referred to is Question 28 NOT Question 34!
In question 28, the substance that dissolves in both aquesous acid and aqueous alkali without evolution of gas must be an amphoteric oxide/hydroxide. (recall that amphoteric oxide/hydroxide reacts with acid as well as alkali to form salt and water). The answers provided are all wrong as there isn't any amphoteric hydroxide given!
I have said before that in the early 90s, there are 5 options in MCQ. option E is zinch hydroxide which is the correct answer!

As for Question 40, page (10)8, there are OH^- ions in the solution. It's just that the concentration of H⁺ ions is much higher since the solution is acidic(pH value of 1).
(Recall that when we analyse the ions present in dilute HCl in electrolysis question, the ions are H⁺, Cl^- and OH^- ions.)

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