Why in the redox titration of $KMnO_4$ vs oxalic acid,do we heat the oxalic acid solution before starting the titration?

$3.92 \, g$ of ferrous ammonium sulphate crystals are dissolved in $100 \, mL$ of water. $20 \, mL$ of this solution requires $18 \, mL$ of $KMnO_4$ during titration for complete oxidation. The weight of $KMnO_4$ present in one litre of the solution is ............. $g$.

An aqueous solution of oxalic acid dihydrate contains $6.3 \ g$ in $250 \ mL$. The volume of $0.1 \ N \ NaOH$ required to completely neutralize $10 \ mL$ of this solution is $.............. \ mL$.

When $10 \ mL$ of an aqueous solution of $Fe^{2+}$ ions was titrated in the presence of dil $H_{2}SO_{4}$ using diphenylamine indicator,$15 \ mL$ of $0.02 \ M$ solution of $K_{2}Cr_{2}O_{7}$ was required to get the end point. The molarity of the solution containing $Fe^{2+}$ ions is $X \times 10^{-2} \ M$. The value of $x$ is $....$ (Nearest integer)

Solution $X$ contains $Na_2CO_3$ and $NaHCO_3$. $20 \ mL$ of $X$ when titrated using methyl orange indicator consumed $60 \ mL$ of $0.1 \ M \ HCl$ solution. In another experiment,$20 \ mL$ of $X$ solution when titrated using phenolphthalein consumed $20 \ mL$ of $0.1 \ M \ HCl$ solution. The concentrations (in $mol \ L^{-1}$) of $Na_2CO_3$ and $NaHCO_3$ in $X$ are respectively:

In an acidic medium, $10 mL$ of $0.25 M$ oxalic acid is titrated with $KMnO_4$ solution. If the volume of $KMnO_4$ solution required to reach the end point is $10 mL$, the strength of the $KMnO_4$ solution is (in $M$)