Assay of Zinc Oxide 

Molecular Formula: ZnO 

Molecular Weight: 81.38 

Assay: Weigh accurately about 1.5 g of zinc oxide and dissolve with 2.5 g of ammonium chloride in 5 mL of 1N H2SO4 with the aid of gentle heat, if necessary. On complete dissolution, add a few drops of methyl orange solution and titrate the excess sulphuric acid with 1N NaOH. The endpoint will be red to yellow. Carry out blank determination omitting zinc oxide sample. The difference in the two titrations indicates the amount of 1N H2SO4 reacting with zinc oxide. 


ZnO  + H2SO4 → ZnSO4 + H2O + H2SO4 (Excess) 

H2SO4 +  2NaOH → Na2SO4 + 2H2O  (Factor)


1 Mole of H2SO4 ≅ 1 Mole of zinc oxide 

1000 mL of 1M H2SO4 ≅ 81.38 g of ZnO 

1 mL of 1N H2SO4 ≅ 0.04069 g of ZnO

Make sure you also check our other amazing Article on : Assay of Sodium Benzoate (aqueous)
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