Assay of Milk of Magnesia

Molecular formula: Mg(OH)2 

Molecular Weight: 58.34 

Assay: Weigh accurately about 5 g milk of magnesia in a tared stoppered flask and shake with 25 mL of sulphuric acid for 10 minutes. After completion of the reaction titrate excess sulphuric acid with 1 N NaOH using methyl red as an indicator. The endpoint will be red to yellow. Carry out blank determination omitting milk of magnesia sample. The difference in two titrations indicates the amount of 1N H2SO4 reacting with milk of magnesia. 


Mg(OH)2 + H2SO4 → MgSO4 + 2H2O + H2SO4 (Excess) 

H2SO4  + 2NaOH → Na2SO4  + 2H2

Factor Calculation: 

1 Mole of H2SO4 ≅ 1 Mole of milk of magnesia

1000 mL of 1M H2SO4 ≅ 58.34 g of Mg(OH)2

1 mL of 1M H2SO4 ≅ 0.05834 g of Mg(OH)2

Make sure you also check our other amazing Article on : Assay of Citric Acid (Anhydrous)
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