50 mL of a solution containing 1 g each of ${\mathrm{Na}}_2{\mathrm{CO}}_3,{\mathrm{NaHCO}}_3$ and NaOH was titrated with N-HCl. What will be the titre reading when only phenolphthalein is used as indicator ?

At the end point using phenolphthalein as indicator uses complete NaOH and $\frac{1}{2}\mathrm{Meq}.\mathrm{of}{\mathrm{Na}}_2{\mathrm{CO}}_3.$

$\begin{array}{l}\therefore \mathrm{Meq}.\mathrm{of}\mathrm{NaOH}+\frac{1}{2}\mathrm{Meq}.\mathrm{of}{\mathrm{Na}}_2{\mathrm{CO}}_3=\mathrm{Meq}.\mathrm{of}\mathrm{HCl}\\ \frac{1}{40}\times 1000+\frac{1}{2}\times \frac{1}{106}\times 2\times 1000=\mathrm{V}\times 1\\ \therefore \mathrm{V}=34.4\mathrm{ml}\end{array}$