Question

a compound contain 84.2% boron and 15.7% hydrogen.its molar mass is 76.7%, write its empirical and molecular formula​

Answer 1

Explanation:

Percentage of boron in the compound = 84.2%

Percentage of hydrogen in the compound = 15.7%

Therefore, in 100 g of compound:

Mass of boron = 84.2 g

Mass of hydrogen = 15.7 g

Moles of boron = mass/ molar mass

= 84.2/10.8

= 7.79

Moles of hydrogen = 15.7/1

=15.7

Ratio of moles of boron and hydrogen = 7.79 : 15.7

= 1:2

Thus the empirical formula of compound = BH2

Empirical formula mass = 10.8 + 2 x 1

= 12.8 u

Molecular mass = 76.7 u

n = molecular mass/empirical formula mass

= 76.7/12.8

= 5.99 = 6

Molecular formula = (empirical formula)n

= (BH2)6

= B6H12

hope it help you mate