Assay of Aspirin

Molecular formula: C9H8O4 

Molecular Weight: 180.2 

Assay: Weigh accurately about 1.5 g, dissolve in 15 mL of ethanol (95%), add  50.0 mL of 0.5 M sodium hydroxide, boil gently for 10 minutes, cool, and titrate the excess of alkali with 0.5 M hydrochloric acid using phenol red solution as indicator. Repeat the operation without the substance under examination. The difference between the titrations represents the amount of sodium hydroxide required. 


Factor Calculation: 

2 Moles of NaOH ≅ 1 Mole of aspirin 

2000 mL of 1M NaOH ≅ 180.2 g of C9H8O4    

1 mL of 0.5 M NaOH ≅ 0.04504 g of C9H8O4 

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