need help in A level Chem Qns replied by UltimaOnline @ Sun, 08 Jun 2008 11:46:31 +0800

UltimaOnline — Sun, 08 Jun 2008 11:46:31 +0800

Greets, Moderator Eagle!

need help in A level Chem Qns replied by eagle @ Sun, 08 Jun 2008 10:38:05 +0800

eagle — Sun, 08 Jun 2008 10:38:05 +0800

Originally posted by UltimaOnline:

I'm an 'A' level (and 'O' level) Chem teacher-tutor, ex-MOE. The qn u asked, is a Hwa Chong JC Prelim Qn.

Great!

We need more chem help. Welcome!

need help in A level Chem Qns replied by UltimaOnline @ Sat, 07 Jun 2008 02:13:46 +0800

UltimaOnline — Sat, 07 Jun 2008 02:13:46 +0800

You're welcome :)

Btw, for the most 'delightful' or 'enjoyable' O.C. deductive/elucidation qn ever (and I thought SRJC was sadistic), look up CJC's Paper 3. The corresponding HCJC and RJC O.C. qns, in comparison, are (relatively) nondescript, and would be much preferred (appreciated!) in the actual A Level exams.

need help in A level Chem Qns replied by arigatoast @ Fri, 06 Jun 2008 16:13:03 +0800

arigatoast — Fri, 06 Jun 2008 16:13:03 +0800

Hi ultimaonline. Thanks for your help.

1) Of the 3 gases, only 1 of them will remain gaseous at room temp.

This is the key idea i miss out. Thanks.

Btw the ans is A.

(101kPa x 4dm3)/R423 x (R298)/14.09dm3

= 20.199kPa.

need help in A level Chem Qns replied by UltimaOnline @ Thu, 05 Jun 2008 22:53:20 +0800

UltimaOnline — Thu, 05 Jun 2008 22:53:20 +0800

(my post kena truncated above)

Q31 here

http://infinity.usanethosting.com/forum/messages/468.html

Q33 here

http://infinity.usanethosting.com/forum/messages/470.html

Full solutions posted on my website.

The thing about gas law qns, is that you have to be careful about the units. If you use pressure in atm and volume in dm3, the value of gas constant R is 0.0821. Most of the time however, you use pressure in pascals (not kPa) and volume in m3 (1 m3 = 1,000 dm3 = 1,000,000 cm3), in which case the value of gas constant R is 8.31. Be careful your units when doing gas law qns!

Chemistry is probably the most fun subject to take at 'A' level, followed by Biology. Most of the other subjects at the JC level aren't quite as enjoyable.

need help in A level Chem Qns replied by UltimaOnline @ Thu, 05 Jun 2008 22:50:42 +0800

UltimaOnline — Thu, 05 Jun 2008 22:50:42 +0800

I'm an 'A' level (and 'O' level) Chem teacher-tutor, ex-MOE. The qn u asked, is a Hwa Chong JC Prelim Qn.

Instead of writing out the full solution, I'll just give you some guidelines.

1) Of the 3 gases, only 1 of them will remain gaseous at room temp.

2) Using PV = nRT, determine the number of moles of this gas. (what is the volume you should use? think!)

3) When the vessels are connected at the new (room) temperature, use PV = nRT again to calculate the new pressure, now that you know 'n'. (what is the new volume you should use? think!)

This is a pretty good question, as far as gas law qns go. I wrote a couple of my own gas law qns... (truncated...)

need help in A level Chem Qns replied by arigatoast @ Wed, 04 Jun 2008 13:57:52 +0800

arigatoast — Wed, 04 Jun 2008 13:57:52 +0800

3 vessels containing 90cm3 of iodine fumes, 4dm3 of argon and 0.01m3 of water vapour respectively at 150 degree celsius and 101 kPa were connected together.

The connected vessels were allowed to cool to room temp. What was the final pressure in the connected vessel.

A) 20.2kPa

b) 71.1kPa

c)28.7kPa

d)70.7kPa

I shall not reveal the answer as it might affect the way u calculate... i keep getting the wrong option. The correct ans will be revealed when someone got the correct option.

Thanks all for help.