A-level Chemistry Avogadro constant

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tooticky
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#1
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#1
Hi,
I have this question:

Which statement gives the numerical value of the Avogadro constant?
A - The number of moles in 12g of carbon 12
B - The number of electrons lost by 20.05g of calcium when it reacts with oxygen
C - The number of molecules in 16g of oxgyen
D - the number of atoms in 1 mole of chlorine molecules

The answer is B. I can figure out why it's not any of the others, but I'm not 100% certain on my reasoning for why B works. Would anyone mind talking it through?

Thanks!
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anomaly--1
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#2
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Hi so what I did was 20.05/40.1 which gives you 0.5moles. And becuase Ca can lose 2electrons multiple 0.5 x 2 to give you 1 mole. Which is equal o avagadros constant I think. You might want to check my working as I’m in yr 12 and found this difficult and I have June end of years soon. Is this from an AS paper
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Pigster
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(Original post by anomaly--1)
Hi so what I did was 20.05/40.1 which gives you 0.5moles. And becuase Ca can lose 2electrons multiple 0.5 x 2 to give you 1 mole. Which is equal o avagadros constant I think. You might want to check my working as I’m in yr 12 and found this difficult and I have June end of years soon. Is this from an AS paper
You're all good.

It might be worth adding why t'other three are wrong.

a) there is 1 mol in 12 g of C-12 rather than 6.02 x10^23 mol in 12 g of C-12
c) 16 g of O2 is 0.5 mol, since Mr = 32, rather than using Ar = 16
d) 1 Cl2 molecule contains 2 atoms, so here you have 2 mol of atoms
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tooticky
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#4
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(Original post by Pigster)
You're all good.

It might be worth adding why t'other three are wrong.

a) there is 1 mol in 12 g of C-12 rather than 6.02 x10^23 mol in 12 g of C-12
c) 16 g of O2 is 0.5 mol, since Mr = 32, rather than using Ar = 16
d) 1 Cl2 molecule contains 2 atoms, so here you have 2 mol of atoms
Thank you both! I think I was overthinking it
anomaly--1 this is from an A-level paper! Good luck on your end of year exams!
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