Comments on: O Levels Chemistry – Selected Exam Questions

By: Harshada Adel

Harshada Adel — Mon, 14 Nov 2011 07:04:22 +0000

Question 1)Ans is C;Though CO2 and SO2 both result for the acidity of acid rain,it is mainly because of SO2.When CO2 dissolve in water it will form carbonic acid and when SO2 gets dissolved in water it will finally form sulfuric acid.As sulfuris acid is much more acidic than carbonic acid,SO2 IS THE COORECT ANS I FILL…
Question 2:Ans C;Aluminium is an reducing agent.When Nitrates in NaOH solution are treated with Al Nitrates are reduced to Ammonia gas.This is a special test used to detect the nitrates called Devardas test.

By: sean

sean — Wed, 05 May 2010 16:39:19 +0000

One of them is an AMPHOTERIC Oxide – it will react with both acids and alkalis.

Think about it.

By: png

png — Sun, 17 Jan 2010 14:00:32 +0000

I hope my answers are not too late. For question 1, CO2 will not be accepted because in our air, this is already a small percentage of CO2, so we do not consider it that acidic. SO2 is chosen because SO2 forms H2SO3 in water which is much more acidic than HCO3-, thus it is much safer to choose SO2.

As for question 2, I learnt it in class 2/3 years ago. It’s a reaction that is not required of O level candidates. (:

By: sean

sean — Thu, 15 Oct 2009 05:34:19 +0000

Hi Al Nasr Ahmed,

See my reply to Marcus & Jie below.

All the best to your Chemistry,
Sean Chua =)

By: sean

sean — Thu, 15 Oct 2009 05:33:42 +0000

Hi Marcus,

Your reasoning for the question on Zinc Oxide is correct.
Keep it up!

For the question on photography chemistry, your steps in analysis is also spot on. Answer would be options 2 in which Ag+ ions has been reduced to Ag after taking in electrons.

Hope this information helps.

To Your Academic Success in Chemistry,
Sean Chua =)