Question

What is the empirical formula of a compound that is made of 3.80g of phosphorus and 0.371g of hydrogen?

Answer 1

You start by diving each quantity given by the atomic wight of each element:

Phosphorus (P)   $\frac{3.8}{31} =0.123$

Hydrogen (H)   $\frac{0.371}{1} =0.371$

Then you divide by the lowest number:

$\frac{0.123}{0.123} = 1$ for phosphorus

$\frac{0.371}{0.123} = 3$ for hydrogen

So the empirical formula will be:    

$PH_{3}$