At `25^(@)C` find pH of resultant solution prepared by mixing 50 ml, 0.2 M kA(aq) and 50 ml, 0.2M kB(aq) solution : (given = `K_(a)(HA)=5xx10^(-9), K_(a)(HB)=1.25xx10^(-9)`)

Options

A. 3
B. 2.5
C. 11
D. 6

Answer

D

Explanation

`"pH of "(NaHCO_(3))=(1)/(2)[pKa_(1)+pKa_(2)]`
`(1)/(2)[pKa_(1)+pKa_(2)]=9`
`pKa_(1)+underset(LR)(pKa_(2))=18`
`H_(2)CO_(3)+NaOH rarr NaHCO_(3)`
`{:(44,40,,-),(4,0,,40):}`
Buffer `rarr pH = pKa_(1)+log.(40)/(4)`
`pH=pKa_(1)+log.(40)/(4)`
`pH=pKa_(1)+log10`
`7.6 = pKa_(1)+1`
`pk_(a_(1))=6.6`
`18=6.6 + pk_(a_(2))`
`pk_(a_(2))=11.4`