Question

$5.00mL$ of $0.10M$ oxalic acid solution taken in a conical flask is titrated against $\mathrm{NaOH}$ from a burette using phenolphthalein indicator. The volume of $\mathrm{NaOH}$ required for the appearance of permanent faint pink color is tabulated below for five experiments. What is the concentration, in molarity, of the $\mathrm{NaOH}$ solution?

Experiment number	Volume of $\mathrm{NaOH}$ (mL)
$1$	$12.5$
$2$	$10.5$
$3$	$9.0$
$4$	$9.0$
$5$	$9.0$

Answer 1

Calculate the molarity of NaOH solution:

Volume of $\mathrm{NaOH}$ used $=9.0mL$

At equivalence point,

number of equivalents of Oxalic acid = number of equivalents of $\mathrm{NaOH}$

${\mathrm{M}}_1{\mathrm{V}}_1{\mathrm{Z}}_1={\mathrm{M}}_2{\mathrm{V}}_2{\mathrm{Z}}_2$

where $M_1,M_2=$molarity of oxalic acid, $\mathrm{NaOH}$ respectively

$V_1,V_2=$Volume of oxalic acid, $\mathrm{NaOH}$ respectively

$Z_1,Z_2=$Z-factor of oxalic acid, $\mathrm{NaOH}$ respectively

$$\begin{gathered} 0.1\times 5\times 2=M_2\times 9\times 1 \\ \Rightarrow M_2=0.11 \end{gathered}$$

Thus, the molarity of $\mathrm{NaOH}$ solution is $0.11M$.