A chloride of silicon contains 79.1 mass % Cl. (a) What is the empirical formula of the chloride? (b) If the molar mass is 269 g/mol, what is the molecular formula?

Empirical SiCl3

Molecular Si2Cl6

Explanation:

Since it contains 79.1% chlorine, this means it contains (100 - 79.1)% silicon = 20.9% chlorine

To get the empirical formula, we firstly need to know the atomic masses of both chlorine and silicon. This is 35.5 and 28

We then divide the percentage abundances by the corresponding atomic masses.

Cl = 79.1/35.5 = 2.23

Si = 20.9/28 = 0.75

We then divide by the smallest, which is 0.75

Cl = 2.23/0.75 = 3

Si = 0.75/0.75 = 1

The empirical formula is thus SiCl3

To get the molecular formula:

(28+3(35.5))n = 269

134.5n = 269

n = 269/134.5 = 2

The molecular formula is Si2Cl6