How much of `0.3M` ammonium hydroxide should be mixed with 30 mL of `0.2M` solution of ammonium chloride to give buffer solutions of `pH 8.65` and 10 ? (Give: `pK_(b) of NH_(4)OH=4.75`)

Answer

112.5 mL

Explanation

`pOH = 14 - pH = 14 - 0 = 4 `
`pOH = pK_(b) + log .(["Salt"])/(["Base"]), 4= 4.75 + log.(["Salt"])/(["Base"]) or log.(["Salt"])/(["Base"]) = - 0.75 = 1.25 or (["Salt"])/(["Base"]) = 0.1778`
i.e.,`("Moles of salt")/("Moles of base")=0.1778 or ((0.2)/(1000)xx30)/((0.3)/(1000)xxV)=0.1778` or `V = 112.5 ml`