Question

The elements A and Z combine to produce two different compounds: A2Z3 and AZ2. If .15 mol of A2Z3 has a mass of 15.9g and .15 mole of AZ2 has a mass of 9.3g, what are the atomic masses of A and Z?

Could somebody please help me with this? Can I make a system of equations to solve it, or do I need to do something different? I'm lost. =(

Answer 1

So from the data, you know
.3A+.45Z=15.9
.15A+.30Z=9.3

check my thinking.

Answer 2

Let those atomic masses be A and Z. Here are the two equations you can write:

15.9/0.15 = (2/5)A + (3/5)Z
(Do you see why? 15.9/0.15 = 106 is the molar mass of A2Z3.)

9.3/0.15 = 62 = (1/3)A + (2/3)Z

Rewrite as
530 = 2 A + 3 Z
186 = A + 2 Z

Take it from there.

Answer 3

I think I've got it, thank you!