Question

A pure sample of a compound is found to contain 1.11x1022 nitrogen atoms of and 2.22x1022 oxygen atoms. What is the empirical formula of the compound?

Answer 1

 The empirical formula of the   compound is NO₂

calculation

Step 1: find the moles  of  Nitrogen and oxygen using the Avogadro's law constant

That is according to Avogadro's law   1 mole = 6.02 x 10²³  atoms

The  moles of nitrogen (N)  is calculated  as below

= 1  mole = 6.02 x 10²³ atoms

   ? moles= 1.11 x 10²²  atoms

by cross multiplication

= {(1 mole  x 1.11 x10²²  atoms)  / 6.02 x 10²³  atoms}  = 0.0184  moles

moles of oxygen  is calculated as below

1 mole  = 6.02 x 10 ²³  atoms

? moles= 2.22 x 10²² atoms

by cross multiplication

={ (1 mole x 2.22 x 10²² atoms) / 6.02 x 10²³}  = 0.0369 moles

Step 2: find the mole ratio  of N to O by dividing each mole by smallest number of mole (0.0184)

That is;

        for  N  = 0.0184 /0.0184 = 1

       for O =0.0369/0.0184  =2

Therefore the empirical formula = NO₂