Question

Aspirin can be prepard from salicylic acid `(C_(7)H_(6)O_(3))` and acetic anhydride `(C_(4)H_(6)O_(3))` according to the equation
`2C_(7)H_(6)O_(3)+C_(4)H_(6)O_(3)rarr2C_(9)H_(8)O_(4)+H_(2)O`
This reaction gives a yield of `74%`, provided that a `50%` excess of acetic anhydride (the cheaper reagent) is used. If a chemist wants to prepare `20.0g` of aspirin in the laboratory, what mass of the of acetic anhydride should be use ?
A. `20.7g`
B. `11.5g`
C. `23.0g`
D. `7.65g`

Answer 1

Correct Answer - B
`2C_(7)H_(6)O_(3)+C_(4)H_(6)O_(3)rarr2C_(9)H_(8)O_(4)+H_(2)O`
If 100% yield
360g of Asprine required`=102g` of acetic anhydried
1g of Asprine required `=(102)/(360)g` of acetic anhydried
20g of Asprine required `=(102)/(360)xx20g` of acetic anhydried
But for 74% yield acetic anhydride required is =7.657g
But chemist taking 50% exceeds, So `=7.65+7.65xx(500)/(100)=11.5g`