Question

$50 \,mL$ of a solution containing $1\, g$ each of $Na_2CO_3, NaHCO_3$ and $NaOH$ was titrated with $N-HCl$. What will be the titre reading when only phenolphthalein is used as indicator?

• A. $35\, mL$
• B. $32.5\, mL$
• C. $24.5\, mL$
• D. $34.4\, mL$

Answer 1

Answer: (D)

At the end point using phenolphthalein as indicator uses
complete $NaOH$ and $\frac{1}{2}$ Meq. of $Na_2CO_3$.
$\therefore $ Meq.of $NaOH + \frac{1}{2}$meq. of $Na_2CO_3 = $ Meq. of $HCl$
$\frac{1}{40} \times 1000 + \frac{1}{2} + \frac{1}{106} \times 2 \times 1000 = V \times 1$
$\therefore V = 34.4 \,ml$