Question

A compound is 2. 00% H by mass, 32. 7% S by mass, and 65. 3% O by mass. What is its empirical formula? The first step is to calculate the mass of each element in a 100-g sample of the compound. We use 100 g because it makes the calculations more straightforward. What is the mass of each element in a 100. 0-g sample of the compound? mass H = g mass S = g mass O = g.

Answer 1

We assume that there is 100g of the compound (because it makes it easier to calculate) and we turn the percentages into grams.

2% of Hydrogen = 2g of H

32.7% of Sulfur = 32.7g of S

65.3% of Oxygen = 65.3g of O

Now we change the mass of these elements to moles by dividing the mass by the molar mass (which is the value of atomic mass on your periodic table)

2g/1.01g = 1.98 mol

32.7g/32.06g = 1.02 mol

65.3g/16g =4.08 mol

divide all these mol values by the smallest mol value, which is 1.02. (Round the values to whole numbers)

1.98/1.02 = 2 (rounded) of Hydrogen

1.02/1.02 = 1 of Sulfur

4.08/1.02 = 4 of Oxygen

H2SO4 (also known as sulphuric acid) is your empirical formula.