Which sample contains the same number of atoms as 24 grams of carbon?

Question

A)24g Mg
B)80.g Ar
C)4.0g He
D)10.g Ne

i put d but that was wrong....??? help?!?!?

Answer 1

Ok, use the atomic mass of the elements to convert to moles. By definition the ones that have the same # of moles will have the same # of atoms
24g C / 12.01 g C mol-1 = 2.0 moles C
A) 24 g Mg / 24.01 g Mg mol-1 = 1 mol Mg x
B) 80 g Ar / 39.95 g Ar mol-1 = 2 mol Ar
C) 4 g He / 4.00 g He mol -1 = 1 mol He x
The answer is b.

Answer 2

The molecular weight of carbon is about 12. That means a mole of carbon (a certain number of atoms) weighs 12g. Thus, 24g carbon contains 2 moles of atoms.

Molecular weight of Mg is 24. That means 2 moles Mg will weigh 48g. A is wrong.

MW of Ar is 40. That means 2 moles Ar will weigh 80g. B is correct.

MW He is 4. 2 moles He weighs 8 g. C is wrong.

MW Ne is 20. 2 moles Ne weighs 40g. D is wrong.