Equilin is an estrogen isolated from the urine of pregnant mares. The percent composition of equilin is 80.56 percent C, 7.51 percent H, and 11.92 percent O. What is its molecular formula if its molar mass is approximately 268 g/mol

The correct answer is C18H20O2.

Explanation:

Based on the given information, one hundred grams of equilin contains 80.56% Carbon, 7.51% Hydrogen, and 11.95% Oxygen. Thus, by mass it comprises 80.56 g Carbon, 7.51 g Hydrogen, and 11.92 g Oxygen.

The molecular mass of carbon, hydrogen, and oxygen are 12.01 g/mol, 1.008 g/mol, and 16.00 g/mol.

The moles of the elements present can be determined by using the formula,

Moles = Weight/Molecular mass

Moles of C = 80.56 g/12.01 g/mol = 6.708 mol

Moles of H = 7.51 g/1.008 g/mol = 7.45 mol

Moles of O = 11.92 g/16 g/mol = 0.745 mol

This gives the formula of C6.708H7.45O0.745. By dividing the subscripts from the smallest value, the possible whole numbers obtained will be,

6.708/0.745 = 9, 7.45/0.745 = 10, 0.745/0.745 = 1. Now the empirical formula obtained will be, C9H10O

Now dividing the molar mass of equilin, that is, 268 g/mol from the empirical formula mass, that is, 9*12.01 g/mol + 10*1.008 g/mol+ 16.00 g/mol = 134.2 g/mol, we get,

268/134.2 = 2

Now by multiplying the subscripts in the empirical formula with 2, the molecular formula obtained will be,

C18H20O2.