Question

) PABA refers to para-aminobenzoic acid which is used in some sunscreen formulations. If a 0.055 M solution of PABA has a pH of 2.96, determine the Ka of PABA. What kind of problem do you think thisis

Answer 1

Answer:
`K_a` of PABA is 0.000022

Step-by-step explanation:

`NH_2C_6H_5COOH\rightarrow H^++NH_2C_6H_5COO^-`

cM 0 0

`c-c\alpha`
`c\alpha`
`c\alpha`

So dissociation constant will be:

`K_a=((c\alpha)^(2))/(c-c\alpha)`

Give c= 0.055 M and
`\alpha` = ?

`K_a=?`

`pH=-log[H^+]`

`2.96=-log[H^+]`

`[H^+]=1.09* 10^(-3)`

`[H^+]=c* \alpha`

`1.09* 10^(-3)=0.055* \alpha`

`\alpha=0.02`

Putting in the values we get:

`K_a=((0.055* 0.02)^2)/((0.055-0.055* 0.02))`

`K_a=0.000022`

Thus
`K_a` of PABA is 0.000022