[SLC91]

Hi all,

Perhaps one of you could enlighten me on how to go about answering this question.

How many oxygen atoms would be present in an emerald that has a mass of 60.00g?

mM of Emerald Be₃Al₂(SiO₃)₆ = 537.50 g.mol^-1

The answer keys are:
A. 1.2 x 10²²
B. 4.0 x 10²¹
C. 2.0 x 10²¹
D. 6.7 x 10²⁰

My reasoning goes like this:
If I have 60g of a compound that has a mM of 537.50 g/mol, then I have (60/537.50 =) 0.111 mols of that compound.
For each mole of emerald, I have 18 oxygen atoms, so for 0.111 mols, I have (0.111*18 =) 1.998 mols of oxygens.
Each mole of atoms has 6.022*10^23 atoms, so 18 x (6.022*10^23) = 1.2 x 10²⁴.

As you can see, that's not an option.
Where have I gone wrong?

[mjc123]

Your calculation looks OK to me. Probably the exponent 22 in option A is an error for 24.

[SLC91]

Your calculation looks OK to me. Probably the exponent 22 in option A is an error for 24.

Thanks. I did wonder!