In iodometric titrations, an oxidizing agent such as KMnO₄, ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$, ${\mathrm{CuSO}}_4, {\mathrm{H}}_2{\mathrm{O}}_2$ is allowed to react in neutral medium or in acidic medium which excess of potassium iodide to liberate free iodine KI + oxidizing agent $\to$I₂
Free iodine is titrated against standard reducing agent usually with sodium thiosulphate i.e., 
$$\begin{gathered} {\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7+6\mathrm{KI}+7{\mathrm{H}}_2{\mathrm{SO}}_4\to {\mathrm{Cr}}_2{\left({\mathrm{SO}}_4\right)}_3+4{\mathrm{K}}_2{\mathrm{SO}}_4+7{\mathrm{H}}_2\mathrm{O}+{\mathrm{I}}_2 \\ 2{\mathrm{CuSO}}_4+4\mathrm{KI} \to {\mathrm{Cu}}_2{\mathrm{I}}_2+2{\mathrm{K}}_2{\mathrm{SO}}_4+{\mathrm{I}}_2 \\ {\mathrm{I}}_2+{\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3 \underset{ }{\to }2\mathrm{NaI} + \hspace{0.17em}{\mathrm{Na}}_2{\mathrm{S}}_4{\mathrm{O}}_6 \end{gathered}$$
In iodometric titrations, starch solution is used as an indicator. Starch solution gives blue or violet colour with free iodine. At the end point, blue or violet colour disappears when iodine is completely changed to iodide.