Question

A gaseous compound containing carbon and hydrogen was analyzed and found to consist of 83.65% carbon by mass. The molar mass of the compound is 86.2 g/mol. What is the molecular formula of the compound

Answer 1

Answer:

The molecular formula is C6H14

Explanation:

Step 1: Data given

Suppose the mass of compound = 100 grams

A compound contains:

Carbon = 83.65 % = 83.65 grams

Hydrogen = 16.35 % = 16.35 grams

Atomic mass of carbon = 12.01 g/mol

Atomic mass of hydrogen = 1.01 g/mol

Molar mass of compound = 86.2 g/mol

Step 2: Calculate moles

Moles = mass / molar mass

Moles carbon = 83.65 grams / 12.01 g/mol

Moles carbon = 6.965 moles

Moles hydrogen = 16.35 grams / 1.01 g/mol

Moles hydrogen = 16.19 moles

Step 3: Calculate mol ratio

We divide by the smallest amount of moles

C: 6.965 moles / 6.965 moles = 1

H = 16.19 moles / 6.965 moles = 2.33

This means for 1 mol C we have 2.33 moles H  OR for 3 moles C we have 7 moles H

The empirical formula is C3H7

The molecular mass of this formula is 43.1 g/mol

Step 4: Calculate molecular formula

We have to multiply the empirical formula by n

n = 86.2 g/mol / 43.1 g/mol

n = 2

Molecular formula = 2*(C3H7) = C6H14

The molecular formula is C6H14