1.

A weak base `BOH` is titrated with strong acid `HA`. When `10mL` of `HA` is added, the `pH` is `9.0` and when `25mL` is added, `pH` is `8.0`. The volume of acid required to reach the equivalence point isA. `50mL`B. `40mL`C. `35mL`D. `30mL`

Answer» Correct Answer - D
`{:(BOH+,HArarr,BA+H_(2)O,,),(W_(B),S_(A),("Salt of" W_(B)//S_(A)),,):}`
`[W_(B)` is in excess, so basic buffer is formed]
`pOH = pK_(b) + "log" ([BA])/([BOH]) (pH = 9, pOH = 14 - 9 = 5)`
`5 = pK_(b) + log ((10)/(V - 10)) …(i)`
When `pH = 8, :. pOH = 14 - 8 = 6`.
`6 = pK_(b) + log ((25)/(V - 25))`
Solve equation (i) and (ii),
`V = 30mL`.


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