Compounds of boron with hydrogen are called boranes. One of these boranes has the empirical formula BH_3 and a molecular mass of 28 amu. What is its molecular formula?

#### Solution:

### We will first find the formula mass of the empirical formula, BH_3.

### mass = 10.81\,\text{amu} + (3\times 1.008\,\text{amu})=13.83 amu

### We now know that one molecular unit has a mass of 13.83 amu. To figure out how many units are in 28 amu, we simply dividing 28 amu by 13.83 amu.

### \frac{28\,\text{amu}}{13.83\,\text{amu}}=2.02\approx 2

### This means the molecular formula is (BH_3)_2. Another way to write this would be, B_2H_6