Question

If the molar mass of lindane is 290g/mol and the percent composition is 24.8% C,2.08% H, and 73.1% Cl, what is the molecular formula of lindane?

Answer 1

First, find out how many moles of each atom you have, assuming you have 100g of lindane. To do this, divide each atom's mass by its molar mass.

Amount of C `= 24.8/12.01 = 2.06` mol

Amount of H `= 2.08/1.01 =2.06` mol

Amount of Cl `= 73.1/35.45 = 2.06` mol

Now put these amounts into a ratio. This is pretty easy as all the amounts are 2.06 mol, so the ratio is 1:1:1. From this, we can see the empirical formula is CHCl.

Now, divide the molar mass of 100g of lindane by the molar mass given in the question.

Molar mass of 100g of lindane = 12.01+1.01+35.45 = 48.47 g/mol

`290/48.47 = 5.98` (roughly 6)

So the molecular formula is 6 times the empirical formula, giving a ratio of 6:6:6

The molecular formula of lindane is `C_6H_6Cl_6`