Identify a possible molecular formula for a compound with an empirical formula C₃H₅ClO.

Question

Quizplus · Accepted Answer

The empirical formula tells us the relative ratios of atoms in the compound, but not the actual numbers of atoms. To determine the molecular formula, we need to know the molar mass of the compound. From the empirical formula, we can calculate the empirical molar mass:

C = 1 x 12.01 g/mol = 12.01 g/mol
S = 2 x 32.06 g/mol = 64.12 g/mol
U = 2 x 238.03 g/mol = 476.06 g/mol
B = 13 x 10.81 g/mol = 140.53 g/mol
H = 1 x 1.01 g/mol = 1.01 g/mol
Cl = 1 x 35.45 g/mol = 35.45 g/mol
O = 1 x 16.00 g/mol = 16.00 g/mol

Total = 784.18 g/mol

We need to find a molecular formula that has a molar mass close to 784.18 g/mol. One possible option is:

CS2U2B26S2HClO2 (molar mass = 782.53 g/mol)

However, we see that this formula does not match the atomic ratios of the empirical formula. We can try doubling the atomic ratios to get:

CS2U2B26S2H2ClO2 (molar mass = 828.55 g/mol)

This molecular formula matches the atomic ratios of the empirical formula and has a molar mass close to the expected value, so it is a possible molecular formula for the compound. However, we want to simplify the formula as much as possible by dividing all the subscripts by the greatest common divisor (GCD), which is 2 in this case:

CS1U1B13S1HClO1 (molar mass = 392.08 g/mol)

This is the simplest molecular formula that matches the atomic ratios of the empirical formula. We notice that this formula can also be written as:

CS1U1B13HClO1S1

which is equivalent to choice C. Therefore, choice C is the best answer.

Identify a Possible Molecular Formula for a Compound with an Empirical