Question

A compound of lead has the following percentage composition, Pb = 90.66 % ; O = 9.34 %. Calculate the empirical formula of the compound. [Pb = 207 ; O = 16].

Answer 1

Hint: The empirical formula gives the minimum number of atoms of each element that must combine to give the specified compound. By dividing the given percentage with molar mass, we will get the approximate number of atoms of each element in the molecule which will give us the empirical formula of the molecule.

Complete Solution :
The empirical formula gives the minimum number of atoms of each element that must combine to give the specified compound.
We have been given in question that
Pb = 90.66 % and
O = 9.34 %
Molar mass of Lead (Pb) = 207
And molar mass of Oxygen (O) = 16
So, by dividing the given percentage with molar mass, we will get the approximate number of atoms of each element in the molecule.
So, for Pb = $\dfrac{{90.66}}{{207}}$
Pb = 0.44
For ‘O’ = $\dfrac{{9.34}}{{16}}$
O = 0.58

As the number of atoms of ‘Pb’ and ‘O’ is not the same. So, let's divide both by 0.44 to get simplest mole ratio as -
Simplest mole ratio for Pb = $\dfrac{{0.44}}{{0.44}}$
Simplest mole ratio for Pb = 1
Simplest mole ratio for O = $\dfrac{{0.58}}{{0.44}}$
Simplest mole ratio for Pb = 1.32
The ‘O’ moles are in fraction which is not possible. So, to make whole numbers, let us multiply by 3.
So, we have Pb = 3
O = 4
The empirical formula = $P{b_3}{O_4}$

Note: It must be noted that empirical formula in simple terms can be defined as the simple positive integer ratio of atoms present in a compound. The term that we commonly use for molecular formula is a different one. It shows the number of atoms of each type present in a molecule. The empirical formula of two compounds can be the same even if the molecular formula is different.