Thursday, October 4, 2007

Chemistry Questions - Mole Concepts

Try this Mole Concepts O Level Chem questions:

Q) If 2g of hydrogen gas contains x molecules, how many molecules would 2g of nitrogen gas contain?

A) x
B) 7x
C) x/14
D) x/28

Show me the working briefly on how you derive your answer. This way we can determine your concepts for this chapter.


Qn answered under comments


LinwooD said...

hello, who are you? you left me a comment yesterday. anyway, you have a good heart to make this blog :). it helps O level students a lot. especially me. haha.

LinwooD said...

Well, i will try to answer this question.

2g of hydrogen gas = 2H2 = 4 = x
2g of nitrogen gas = 2N2 = 2x14 = 28


since 4=x, therefore,
nitrogen gas is 7x.

well, i dont know whether i did correctly or not though. please correct me if i'm wrong. :D

robobooga said...

hmm... i try...

2g of hydrogen gas = 1 mol =x

2g of nitrogen gas = 2g/28g =1/14 mol

therefore, if 1 mol is x, then 1/14 mol = x/14 #


lijun(: said...

No. of moles of H2 = 2/2 = 1mol
No. of molecules of H2 = (1)(6*10^23) = 6*10^23

let 6*10^23 = x

No. of moles of N2 = 2/28 = (1/14)mol
No. of molecules = (1/14)(6*10^23) = x/14

hence, answer is C.

is it right?

LinwooD said...

hmm i guess it's x/14 too.
i thought its about molar mass.

so what's the right answer actually ?????

Sean Chua said...

Halo Students,

Well Done to all for at least even bother to try it out and sharing with fellow students.

Yup. Answer is indeed C, x/14.

linwood-you can refer to the 2 answers given by robobooga and lijun. Do let me know if you need clarification on it. Stay positive and cheerful as you prepare...