Question

Q1. 100 ml of water sample on titration with N/50 HCl requires 8 mL of acid for phenolphthalein end-point and 9 mL of total acid for methyl-orange end-point. Calculate the type and extent of alkalinity present in water sample.

Answer 1

Here diacidic base is present which give two end point one with phenalphthein and second with methy orange

For phenolphthalein end point-

$\frac{1}{2}\ Meq\ of\ Diacidic\ base = Meq.\ of\ of \ 8ml \ \frac{N}{50}\ HCl$

=$\frac{1\times 8}{50\times1000}=\frac{1}{6225}\ Meq\\$

$Meq.\ of\ Diacidic\ base=2\times Meq.\ of\ HCl=\frac{2}{6225}\ Meq.$

For methyl orange end point-

$Meq.\ of\ monoacidic\ base\ formed=Meq.\ of\ 1ml of\ extra\ HCl\ used$

$=\frac{1\times1}{50\times 1000}=\frac{1}{50000\ Meq.}$

Normality of diacidic alkalinity present in 100 ml water = $\frac{2\times 1000}{6225\times 100}=\frac{20}{6225}=\frac{4}{1245}\ N$