Question

Which sample has the greatest mass? (multiple choice)

A. 1 mol of Na2S
B. 3.0 x `10^24` molecule of O2
C. 8.8 x 10 g of NaCl
D. 1.2 x `10^24` atoms of K

The answer is B. 3.0 x `10^24` molecule of O2, why?

Answer 1

The answer is B.

Explanation:

A

To calculate the mass of 1 mol of `"Na"_2"S"` we need just to multiply it by it's molar mass: 78,0452 g/mol. Therefore the result will be 78,0452 g.

B

To calculate the mass of `"O"_2`, we first need to divide the result by the Avogadro constant.

`3.0 × 10^24color(white)(l) "molecules O"_2 × "1 mol O"_2/(6.022 × 10^23color(white)(l) "molecules O"_2) = "4.98 mol O"_2`

This gives us the moles of `"O"_2`.

Then we multiply by the molar mass.

`"4.98 mol O"_2 × "32.00 g O"_2/"1 mol O"_2 = "160 g O"_2`

C

For C we only have 88 g.

D

And for D the molar mass of `"K"` is 39,0983 g/mol.

This means

`1.2 × 10^24color(white)(l) "atoms" × "1 mol"/(6.022 × 10^23color(white)(l) "atoms") × "39.10 g"/"1 mol" = "80 g"`