Question

Aspirin (acetyl salicyclic acid, molar mass `180 g "mol"^(-1)`) used as analgesic has `pK_(a)` value of 2. Two tablets of aspirin each weighing 90 mg are dissolved in 100 mL of water. The pH of the solution is
A. 0.5
B. `1.0`
C. `2.0`
D. `4.0`

Answer 1

Correct Answer - C
Aspirin is a weak acid. Hence, its pH is given by
`pH=(1)/(2)[pK_(a)-log c]`
Here, `c=2xx0.09 g "in " 100 mL = 1.8 g L^(-1)`
`=(1.8)/(180)M=0.01 M`
`:. pH=(1)/(2) [2-log 0.01]=(1)/(2)[2-(-2)]=2`