Two drops of phenolphthalein was added to 40 " mL of " HCl solution. When 30 " mL of " 0.1 M NaOH was added, part of the the solution turned pink, but colour disappeared on mixing the solutiion. Addition of NaOH was continued drop-wise untill a one-drop addition produced a lasting pink colour, and the colume of NaOH added was 32.56 mL. Calculate
(a). The concentration of HCl solution.
(b). The concentration of HCl solution when 30 mL base was added.
(c). The pH of solution when 30 mL base was added.
(d). The pH of solution when 32.56 mL base was added

Explanation

(a). At the end point:
`m" Eq of "HCl=m" Eq of "NaOH`
`40xxN=01xx1xx32.56`
`N_(HCl)=0.0814`
(b). `m" Eq of "HCl=0.0814xx40=3.256`
`m" Eq of "NaOH added =30xx0.1=3.0`
`m" Eq of "HCl` left`=3.256-3.0=0.256`
`N_(HCl)=(m" Eq of "HCl)/("Total volume")=(0.256)/(30+40)`
`=3.66xx10^(-3)`
`thereforeN_(HCl)=3.66xx10^(-3)`
(c). `pH=-log[H^(o+)]=-log(3.66xx10^(-3))=2.4365`
(d). At the end point `pH=7`.