Question

A compound contains carbon, hydrogen, and chlorine. It has a molar mass of 98.95 g/mol. Analysis of a sample shows that it contains 24.27% carbon and 4.07% hydrogen. What is its molecular formula?

Answer 1

Answer:

C2H4Cl2

Explanation:

Firstly, we know that the compound contains only three elements. These are carbon, hydrogen and oxygen. We have the percentage compositions of carbon and hydrogen, thus we need the one for chlorine. To get the one for chlorine, we simply subtract that of carbon and hydrogen from a total of 100%.

Hence percentage composition of chlorine = 100 - 24.27 - 4.07 = 71.66%

Now, we divide the percentage compositions by the atomic masses. The atomic masses of carbon, hydrogen and chlorine are 12, 35.5 and 1 respectively. We go on to the divisions as follows.

C = 24.27/12 = 2.0225

H = 4.07/1 = 4.07

Cl = 71.66/35.5 = 2.02

We then go on to divide each by the smallest which is 2.02

C = 2.0225/2.02 = 1

H = 4.07/2.02 = 2

Cl = 2.02/2.02 = 1

Hence the empirical formula is CH2Cl

Now, since the molecular mass is 98.95, we need to calculate the molecular formula

Hence, [CH2Cl]n = 98.95

[12 + 2(1) + 35.5]n = 98.95

[12 + 2 + 35.5]n = 98.95

49.5n = 98.95

n = 98.95/49.5 = 2

The molecular formula is thus [CH2Cl]2 = C2H4Cl2