A compound of oxygen and fluorine has a relative molecular mass which is twice that of its empirical formula mass. 105 g of the compound contains 57 g of fluorine. What is the molecular formula of the compound? (Ar values: O = 16; F = 19)

Answer:

22) C

Mass of oxygen = 105 – 57 = 48

To find the empirical formula, we divide the masses of the elements with their Ar.

For fluorine, ⁵⁷/₁₉ = 3
For oxygen, ⁴⁸/₁₆ = 3

Then, we divide all obtained values by the lowest value. In this case, we only receive one value, 3.

So the empirical formula is OF

Since it is relative molecular mass is double of empirical formula mass, the molecular formula would be O₂F₂.