# A-level Chemistry Avogadro constant

Thread starter 1 month ago
#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!
0
1 month ago
#2
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
2
1 month ago
#3
(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
1
Thread starter 1 month ago
#4
(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!
0
X

new posts
Back
to top
Latest

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### Poll

Join the discussion

#### What is missing from the school curriculum?

Basic life skills (eg. cooking) (8)
30.77%
Financial skills (eg. taxes, budgeting) (11)
42.31%
First aid skills (2)
7.69%
Personal safety skills (0)
0%
Sign language (4)
15.38%
Expanded sexual health/relationships (0)
0%
Something else (tell us in the thread) (1)
3.85%