Question

A compound empirical formula is HO. If the formula mass is 34 amu, what is the molecular formula?

Answer 1

Hint: The formula with the simplest whole number ratio of the atoms in any compound is known as the empirical formula. The molecular formula shows the exact number of each atom of each element present in the compound. If we divide the empirical weight by the molecular weight, we’ll obtain a number which would be the no. of Oxygen and Hydrogen atoms present in the compound.

Complete Step By Step Answer:
We are given that the empirical formula of the compound is OH. This is the smallest whole no. ratio of the elements present in the compound. It is said that the molecular formula is always an integral multiple of the empirical formula. Let us first find the empirical weight of the compound.
Empirical weight = atomic weight of Oxygen + atomic weight of Hydrogen
Empirical weight $ = 16 + 1 = 17g/mol $
The molecular weight of the compound is given as 34 amu i.e., 34 g/mol. To find out the molecular formula we’ll use the formula:
 $ Molecular{\text{ }}weight = n \times empirical{\text{ }}weight $
Therefore, $ n = \dfrac{{Molecular{\text{ }}weight}}{{Empirical{\text{ }}weight}} = \dfrac{{34}}{{17}} = 2 $
The value of n was found to be 2. The molecular formula hence can be given as: $ {(OH)_n} = {(OH)_2} = {H_2}{O_2} $
Hence the molecular formula of the compound with empirical formula OH is $ {H_2}{O_2} $
Therefore, the compound given to us is Hydrogen Peroxide.

Note:
The empirical formula makes the stoichiometric calculations very easy and handy. These are of great significance in handling the long chain carbohydrates and proteins. Also, it makes it easy to find the molecular formula, if we find the empirical formula experimentally or by using other tools. Unknown compounds can be easily known by this.