The compound methyl benzoate is used in the manufacture of perfumes. ...

Question

The compound methyl benzoate is used in the manufacture of perfumes. In one

experiment, it is found to consist of 70.58% C, .93% H and 23.49% O, by mass. What

is the empirical formula of this compound? By other experiments, the molar mass

of the compound is found to be 136. What is the molecular formula of the

compound?

Answer 1

To find the empirical formula of methyl benzoate, we assume 100 g of the compound. From the given percentages, we can calculate the masses of each element present in the compound:

mass of C = 70.58 g

mass of H = 0.93 g

mass of O = 23.49 g

Next, we can convert these masses to moles by dividing by their respective molar masses:

molar mass of C = 12.01 g/mol

molar mass of H = 1.01 g/mol

molar mass of O = 16.00 g/mol

moles of C = 70.58 g / 12.01 g/mol = 5.87 mol

moles of H = 0.93 g / 1.01 g/mol = 0.92 mol

moles of O = 23.49 g / 16.00 g/mol = 1.47 mol

We can then divide each of the mole values by the smallest mole value to get the mole ratios:

moles of C / moles of H = 5.87 mol / 0.92 mol ≈ 6.4

moles of H / moles of H = 0.92 mol / 0.92 mol = 1

moles of O / moles of H = 1.47 mol / 0.92 mol ≈ 1.6

The empirical formula of the compound is therefore C6.4H1O1.6, which we can simplify to C16H4O4 by multiplying both subscripts by 2.5.

To find the molecular formula of the compound, we need to know its molar mass. From the problem statement, the molar mass of methyl benzoate is 136 g/mol.

The empirical formula of C16H4O4 has a molar mass of:

(16 x 12.01) + (4 x 1.01) + (4 x 16.00) = 268.32 g/mol

To find the molecular formula, we can divide the experimental molar mass by the empirical formula mass and round to the nearest whole number:

molecular formula multiple = experimental molar mass / empirical formula mass

molecular formula multiple = 136 g/mol / 268.32 g/mol ≈ 0.506

We can multiply the subscripts in the empirical formula by the molecular formula multiple to obtain the molecular formula:

C16H4O4 x 0.506 ≈ C8H2O2

Therefore, the molecular formula of methyl benzoate is C8H2O2.