Question

Analysis of a sample of hydrated salt shows that is contain 4.86g Mg, 6.20g P, and 11.20g O and 5.40g H20. What is formula of the hydrated salts?

Answer 1

First we will convert all the quantities in grams in to moles to evaluate the empirical formula as follows

1. 4.86 g Mg x (1 mol Mg / 24.31 g Mg) = 0.200 mol Mg

2. 6.20 g P x (1 mol P / 30.97 g P) = 0.200 mol P

3. 11.20 g O x (1 mol O / 16.00 g O) = 0.700 mol O

4. 5.40 g H2O x (1 mol H2O / 18.02 g H2O) = 0.300 mol H2O

The formula which comes out to be now is as follows:

Mg(0.200)P(0.200)O(0.700)*0.300 H2O

Now the subscripts we will convert in to lowest number as follows

Mg2P2O7*3H2O This is magnesium sulphate trihydrate