1.

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 ?

Answer»

`20.7g`
`11.5g`
`23.0g`
`7.65g`

Solution :`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`


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