Question

Menthol, the substance we can smell in mentholated cough drops, is composed of C, H, and O. A 0.1005 g sample of menthol is combusted, producing 0.2829 g of CO2 and 0.1159 g of H2O. What is the empirical formula for menthol?

Answer 1

To find the empirical formula of menthol, we need to determine the ratio of the elements present in the compound.

First, let's calculate the number of moles of carbon dioxide (CO2) produced:

Molar mass of CO2 = 12.01 g/mol (1 carbon atom) + 2 * 16.00 g/mol (2 oxygen atoms)

= 12.01 g/mol + 32.00 g/mol

= 44.01 g/mol

Number of moles of CO2 = Mass of CO2 / Molar mass of CO2

= 0.2829 g / 44.01 g/mol

≈ 0.00643 mol

Next, we'll calculate the number of moles of water (H2O) produced:

Molar mass of H2O = 1.01 g/mol (2 hydrogen atoms) + 16.00 g/mol (1 oxygen atom)

= 18.01 g/mol

Number of moles of H2O = Mass of H2O / Molar mass of H2O

= 0.1159 g / 18.01 g/mol

≈ 0.00643 mol

Now, let's determine the ratio of moles between carbon and hydrogen:

Number of moles of carbon = 0.00643 mol

Number of moles of hydrogen = 0.00643 mol * 2 (since there are 2 hydrogen atoms per water molecule)

= 0.01286 mol

To find the simplest ratio, we divide the number of moles by the smallest number of moles (0.00643 mol in this case):

Number of moles of carbon (rounded to nearest whole number) = 1

Number of moles of hydrogen (rounded to nearest whole number) = 2

Therefore, the empirical formula of menthol is CH2.