Question

In a compound of magnesium (Mg = 24) and nitrogen (N = 14), 18 g of magnesium combines with 7g of nitrogen.

Deduce the simplest formula by answering the following questions:

1. How many gram-atoms of magnesium are equal to 18g?
2. How many gram-atoms of nitrogen are equal to 7g of nitrogen?
3. Calculate the simple ratio of gram-atoms of magnesium to gram-atoms of nitrogen and hence the simplest formula of the compound formed.

Answer 1

(a) G atoms of magnesium = `18/24` = 0.75 or `3/4` g-atoms

(b) G atoms of nitrogen = `7/14` = 0.5 or `1/2` g-atoms

(c) As calculated above, 

Simplest ratio of `"g-atom of Mg"/"g-atom of N"`

= `(3/4)/(1/2)`

= `3/4 : 1/2`

∴ Mg : N = 3 : 2

∴ The simplest formula of the compound formed = Mg₃N₂