Question

Aspirin $\left(C_9{H}_8{O}_4\right)$ is prepared by reacting salicylic acid $\left(C_7{H}_6{O}_3\right)$ and acetic anhydride $\left(C_4{H}_6{O}_3\right)$.

$C_7{H}_6{O}_3+C_4{H}_6{O}_3\to C_9{H}_8{O}_4+C_2{H}_4{O}_2$

How many moles of salicylic acid should be used to prepare six 5-grain aspirin tablets? (1 g = 15.5 grains)

• A. $0.01$
• B. $0.1$
• C. $1.0$
• D. $2.0$

Answer 1

Answer: (A)

$0.01$

For aspirin, 1 gram $=$ 15.5 grains.
5 grains $=5\times \frac{1}{15.5}=0.32$ gram
The molar mass of aspirin, $M{M}_{aspirin}=180$ g/mol.

180 g $=$ 1 mol .

For one 5 grains tablet of aspirin $0.32$ g $=\frac{0.32}{180}=0.0018$ mol
0.0018 moles of aspirin are obtained from 0.0018 moles of salicylic acid.
Hence, for 6 tablets the moles of salycilic acid = $6\times 0.0018=0.01$ moles.

Therefore, the option is A.