Acetylene is a colorless gas that is used as a fuel in welding torches, among other things. It is 92.26%C and 7.74% H. Its molar mass is 26.02 g/mol.

Question

What would be the empirical and molecular formula? An explanation would be nice

Answer 1

Empirical formula- for this we need to find the lowest whole number ratio of the elements in the compound.

When given percents, we can assume a 100g sample so that the percents=grams. Then we can find moles of each element using the molar mass from the periodic table. It is important to NOT round at this step.

92.26% C of 100 g sample of gas = 92.26 g C

7.74% H of 100 g sample of gas = 7.74 g H

92.26g C x 1 mol C/12.01 g C= 7.681931724 mol C

7.74 g H x 1 mol H/1.01 g H = 7.663366337 mol H

Since we need the lowest ratio, we divide each mole amount by the smallest amount, in this case the hydrogen.

7.681931724/7.663366337 = 1.002422615 ≈ 1

7.663366337/7.663366337 = 1

The ratio is 1:1 carbon:hydrogen so the empirical formula is CH.

The molecular formula is some multiple of the empirical formula. To find it we divide the molecular mass by the empirical mass. The molecular mass is given (26.02 g/mol). To get the empirical mass us the empirical formula (CH).

1 C = 12.01 g/mol

1 H = 1.01 g/mol

empirical mass = 13.02 g/mol

26.02 g/mol / 13.02 g/mol ≈2

The molecular formula is twice the empirical formula so multiply the subscripts in the empirical formula by 2.

C₁H₁ * 2 = C₂H₂