Empirical and Molecular Formula

Question 1

What are the steps to finding out the empirical formula?

Answer 1

1~ Using the masses given, work out the no. of MOLES of each element.

2~ Find the simplest ratio by dividing all the moles by the SMALLEST MOLE.

3~ This leaves you with a RATIO.

Question 2

If the number of moles are a decimal, what should you multiply to get a whole number?

Answer 2

If close to…

.5 —–> 1/2 —–> x 2
.25 —–> 1/4 —–> x 4
.75 —–> 3/4 —–> x 4
.33 —–> 1/3 —–> x 3
.66 —–> 2/3 —–> x 3

Question 3

1. A compound contains C 62.08%, H 10.34% and O 27.58% by mass. Find its empirical formula and its molecular formula given that its relative molecular mass is 58.

Answer 3

= C = = H = = O =
% by mass: 62.08% 10.34% 27.58%
Mass:
Moles: 5.17333 mol 10.34 mol 1.72375 mol
(Divide all by 1.72)
Simplified ratio: 3 6 1
Ratio of elements: 3 : 6 : 1
Empirical Formula: C₃H₆O

Molecular Formula: C₆H₁₂O₂
12+1+16 = 29
58 / 29 = 2