Question

Given the following empirical formulae and molecular weight, compute the true molecular formulae.

	Empirical formula	Molecular weight
(a)	$C{H}_2$	80
(b)	$C{H}_{2}O$	150
(c)	HO	472
(d)	HgCl	34
(e)	HF	84

Answer 1

The Empirical formula is the simplest formula for a compound. A molecular formula is the same as or a multiple of the empirical formula, and is based on the actual number of atoms of each type in the compound. For example, if the empirical formula of a compound is C₃H₈ , its molecular formula may be C₃H₈ , C₆H₁₆ , etc.

1. For $C{H}_2$ Empirical formula, Molecular weight can be $n\times (12+(2\times 1\left)\right)=14n$ where n is any integer. so $14\times 6=84$

2. For $C{H}_{2}O$ Empirical formula, Molecular weight can be $n\times (12+(2\times 1)+16)=30n$ where n is any integer. so $30\times 5=150$

3. For $HO$ Empirical formula, Molecular weight can be $n\times (16+1)=17n$ where n is any integer. so $17\times 2=34$

4.For $HgCl$ Empirical formula, Molecular weight can be $n\times (200.4+35.5)=235.9n$ where n is any integer. so $235.9\times 2=472$

5.For $HF$ Empirical formula, Molecular weight can be $n\times (19+1)=20n$ where n is any integer. so $20\times 4=80$