Moles Question Solved

Question

A compound of formula M3N contains 0.673 g of nitrogen per gram of the metal M. What is the relative atomic mass of M? Identify M.

Solution

In M3N, 1 mole of nitrogen would be combined with 3 moles of M.

This means, in terms of mass, that 14 g of nitrogen would be combined with a mass of M, equal to that of 3 moles of M.

If 1 g of M was combined with 0.673 g of nitrogen.

Then 14 g of nitrogen would be combined with 20.802 g of M.

From the first line, above, this mass of M is that of 3 moles of M.

Hence molar mass of M = 6.934 g mol-1 and its relative atomic mass is 6.934.

Identity of M is lithium.