38.7% C, 9.7% H, and 51.6% O. Its molecular mass is 62.0 g/mole. A) Determine the empirical formula of the compound. (3 pts) B) What is the molecular formula of the compound?

Question

A coolant widely used in automobile engines contains 38.7% C, 9.7% H, and 51.6% O. Its molecular mass is 62.0 g/mole.

A) Determine the empirical formula of the compound.

B) What is the molecular formula of the compound?

Answer 1

If we assume we have 100 g of the unknown, then %'s become grams and we then find moles of each element to determine the empirical formual.

38.7 g C x 1 mol C/12 g = 3.225 moles C

9.7 g H x 1 mol H/1 g = 9.7 mol H

51.6 g O x 1 mol O/16 g = 3.225 moles O

Divide all by 3.225 to get whole numbers and we end up with...

1 mol C

3 mol H

1 mol O

Empirical formula = CH₃O

To find the molecular formula, we find how many of these empirical formulae "fit into" the given molar mass of 62.0 g/mol. The molar mass of the empirical formula is 12 + 3 + 16 = 31 g/mol. So, it will take TWO of these to make 62.0 g/mol. Thus, the molecular formula is C₂H₆O₂