Question

A compound was found to have 85.7% carbon and 14.3% hydrogen. Its molecular mass is 84. What is its empirical formula? What is its molecular formula?

Answer 1

The molecular formula is C₆H₁₂

The empirical formula is CH₂

Step-by-step explanation:

Percent by mass, means that in 100 g of compound we have:

85.7 g of C

14.3 g of H

Let's make a rule of three with the molar mass to determine the amounts of the elements:

In 100 g of compound we have 85.7 g of C

In 84 g of compound we would have (84 . 85.7) / 100 = 72 g of C

In 100 g of compound we have 14.3 g of H

Then, in 84 g of compound we would have (84 . 14.3) / 100 = 12 g of H

Now let's determine the moles of each element

72 g of C / 12 g/mol = 6 mol of C

12 g of H / 1 g/mol = 12 mol of H

Then, the molecular formula is C₆H₁₂

The empirical formula is CH₂