The concentration of a weak monobasic acid is 0.2(M). If the acid is 2% ionised in the solution, then find the pH of the solution and ionisation constant of the acid.

Explanation

`pOH=1/2pK_b-1/2logc=1/2xx4.74-1/2log(0.01)=3.37`
`pH=14-pOH=14-3.37=10.63`
`[NH_4Cl]=(0.001)/(100)xx1000=0.01(M)`
`pOH=pK_b+log([NH_4Cl])/([NH_4])=4.74+log(0.01)/(0.01)=4.74`
`:.pH=14-4.74=9.26`
`:.` Decrease in pH=10.63-9.26=1.37