Compounds of boron with hydrogen are called boranes


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.

Compounds of boron with hydrogen are called boranes

 

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

 

This question can be found in General Chemistry, 9th edition, chapter 3, question 3.74

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