O-Level Chemistry

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soseducation
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Re: O-Level Chemistry

Post by soseducation » Wed Nov 19, 2014 12:17 pm

KSP2013777 wrote:Somebody can help me to know my understanding correct or not?

Question - Is the number of atoms in 0.5 mol of oxygen gas and 0.5 mol of iron the same?

I think answer is not correct because Oxygen gas is made up of molecules (O2)

That means, 0.5 mol of oxygen gas have 0.5 x 2 x 6 x 10^23 = 6 x 10^23 oxygen atoms.

But, 0.5 mol of iron have 0.5 x 6 x 10^23 = 3 x 10^23 iron atoms.

So, answer is no, am I right? pls ans when u hv time.

Yes, you are right. The key word in the question is ATOMS. not molecules not ions. Oxygen itself is made up of two atoms since it is diatomic and you have to take that into consideration. :smile:

KSP2013777
OrangeBelt
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Re: O-Level Chemistry

Post by KSP2013777 » Wed Nov 19, 2014 2:00 pm

soseducation, thanks. I so scared my answer is wrong

soseducation
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Re: O-Level Chemistry

Post by soseducation » Wed Nov 19, 2014 5:53 pm

KSP2013777 wrote:soseducation, thanks. I so scared my answer is wrong
Don't worry. Be confident of yourself! :imcool:

SavedbyGrace
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Re: O-Level Chemistry

Post by SavedbyGrace » Thu Nov 20, 2014 9:54 pm

Pls PM me for O level Secondary School Pure Chemistry materials including exam papers, worksheets, higher order questions, textbook and TYS.

ChiefKiasu
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Re: O-Level Chemistry

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KSP2013777
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Re: O-Level Chemistry

Post by KSP2013777 » Fri Nov 28, 2014 8:42 am

What is the number of moles in 1.42g of chlorine gas? Because there are 2 chlorine atoms in 1 molecule, so 1.42 ÷ ( 2 × 35.5 ) = 0.02 mol
My understanding is correct or not?
Pls answer when u have time.
Tks

hmong
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Re: O-Level Chemistry

Post by hmong » Fri Nov 28, 2014 11:39 am

no of moles = mass/Mr

1.42 ÷ ( 2 × 35.5 ) = 0.02 mol of chlorine molecules

If they ask what are the number of moles of atoms then will need one more working.- multiply by 2.

KSP2013777
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Re: O-Level Chemistry

Post by KSP2013777 » Fri Nov 28, 2014 9:50 pm

Thank you, hmong, for yr answer.

KSP2013777
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Re: O-Level Chemistry

Post by KSP2013777 » Sun Nov 30, 2014 5:17 pm

Now I little bit worry. How u know answer they want is moles of chlorine molecules or moles of chlorine atoms. This question never say which one... so can give any one answer?

KSP2013777
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Re: O-Level Chemistry

Post by KSP2013777 » Sun Nov 30, 2014 6:08 pm

How many atoms are there in 2 moles of ammonia gas?

My friend say 2 X 6 X 10^23 = 12 × 10^23 atoms

But I think must break up NH3 first

Hydrogen : 2 × 6 × 10 ^ 23 = 12 × 10 ^ 23 hydrogen atoms
Nitrogen : 2 × 3 × 6 × 10 ^ 23 = 36 × 10^23 nitrogen atoms
total atoms = 48 × 10^23 atoms

We argue long time about this. Who correct? My friend or I?

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