Which sample has the greatest mass? (multiple choice)

A. 1 mol of Na2S
B. 3.0 x 1024 molecule of O2
C. 8.8 x 10 g of NaCl
D. 1.2 x 1024 atoms of K

The answer is B. 3.0 x 1024 molecule of O2, why?

1 Answer
KiraTiss · Ernest Z.
Feb 17, 2016

The answer is B.

Explanation:

A

To calculate the mass of 1 mol of Na2S 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 O2, we first need to divide the result by the Avogadro constant.

3.0×1024lmolecules O2×1 mol O26.022×1023lmolecules O2=4.98 mol O2

This gives us the moles of O2.

Then we multiply by the molar mass.

4.98 mol O2×32.00 g O21 mol O2=160 g O2

C

For C we only have 88 g.

D

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

This means

1.2×1024latoms×1 mol6.022×1023latoms×39.10 g1 mol=80 g

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