Comments on: O Level Chemistry – Mini Series on Tough MCQs Part 4

By: Harshada Adel

Harshada Adel — Mon, 14 Nov 2011 07:38:38 +0000

uestion 1)Ans:B;Ba2+ forms insoluble barium sulfate with sulfuric acid While othyer metals will show a simple displacement reaction to give aqueous metal sulfates with the liberation of hydrogen.
Question 2)Ans. A;Aluminium is a reducing aent and it will resuce the nitrates into ammonia.

Question 3)Ans A;Among the following choices co2 has the heighest molcular weight which accounts for its heighest density as compared with other..Also in any test which result in the formation of CO2 it was observed thet CO2 alway sinks down with the o2 pushed up if any.Since the one sinks below the other is with higher density its the correct ans..

By: Harshada Adel

Harshada Adel — Mon, 14 Nov 2011 07:34:51 +0000

Question 1)Ans:B;Ba2+ forms insoluble barium sulfate with sulfuric acid While othyer metals will show a simple displacement reaction to give aqueous metal sulfates with the liberation of hydrogen.
Question 2)Ans. A;Aluminium is a reducing aent and it will resuce the nitrates into ammonia.

By: zainub

zainub — Fri, 24 Apr 2009 12:40:38 +0000

im from Pakistan….and im doin GCE o-levels….yeah thanx alot its all clear now….Infact i gave dat explanation dat u have given here to my skool teacher n she agreed to it….Thanx to u dat now all my classmates know da right answer…

By: sean

sean — Fri, 24 Apr 2009 07:19:36 +0000

Hi zainub,

Where are you from? Singapore Secondary School?

In GCE O Levels Syllabus, we will calculate the MR of the gases and compare to check their density (lightness).

You are right that main gases in AIR is nitrogen (N2) and oxygen (O2), with a percentage composition of about 78% and 21% respectively.

MR of N2 = 28
MR of O2 = 32

Average MR of N2 + O2 in AIR = (78/100 * 28) + (21/100 * 32)
= 21.84 + 6.72
= 28.56

If you compare it to the MR of Carbon Dioxide (CO2) of 44, you realised that AIR is “lighter” than carbon dioxide.

Hope the above explanation is clear to you.

Let me know how you think.

To Your Academic Success in Chemistry.
Sean Chua
Master Trainer & Author
WINNERS Education Group

“Experience Learning with A Difference”

By: zainub

zainub — Tue, 07 Apr 2009 16:47:53 +0000

I am a bit confused. My chemistry teacher has taught us that Carbon dioxide is lighter
than air. Air has Mr greater than 60. The main gases in air are Nitrogen and Oxygen
and if we calculate their respective Mr they sum up to (28 + 32 = 60) 60 where as
the Mr of Carbon dioxide is 44. 44 < 60 therefore, carbon dioxide is lighter than air…