Question

A solution of an acid has `pH= 4.70`. Find out the concentration of `OH^(-)` ions `(pK_(w)=14)`.
A. `5 xx 10^(-10)`
B. `4 xx 10^(-10)`
C. `2 xx 10^(-5)`
D. `9 xx 10^(-4)`

Answer 1

Correct Answer - A
`pH=4.70 implies -log [H^(+)]=4.70`
`:. log[H^(+)]=-4.7 =bar(5).30`
or `[H^(+)]=1.999xx10^(-5)~~2 xx 10^(-5)`
`pK_(w)=14 implies [H^(+)]xx[OH^(-)]=10^(-14)`
`:. [OH^(-)]=(10^(-14))/(2 xx 10^(-5))=0.5 xx 10^(-9) = 5 xx 10^(-10)`