A detailed visual teaching resource explaining how an iodometric titration can be used to determine the concentration of a colourless oxidising solution, using potassium iodate(V), KIO₃, as the worked example.

The resource follows the complete analytical sequence from the original oxidising solution to the final concentration calculation.

A measured 25.0 cm³ sample of the oxidising solution is transferred to a 250 cm³ volumetric flask, reacted with excess iodide ions in acidic solution and made up to the calibration mark with distilled water. After thorough mixing, 25.0 cm³ aliquots are removed for titration.

The poster explains:

how an oxidising agent converts iodide ions, I⁻, into iodine, I₂
why iodide ions are added in excess
preparation and correct mixing of the solution in a volumetric flask
taking representative aliquots for titration
titration of the liberated iodine with standard sodium thiosulfate solution
addition of starch indicator near the endpoint
the colour changes from brown iodine through pale yellow and blue-black to a colourless endpoint
construction and use of the relevant ionic and half-equations
mole relationships between iodate(V), iodine and thiosulfate
working backwards from the thiosulfate titre to determine the concentration of the original oxidising solution

The important stoichiometric relationships are clearly developed:

IO₃⁻ : I₂ : S₂O₃²⁻ = 1 : 3 : 6

The resource emphasises the logical chain behind iodometric analysis:

Oxidising agent → iodine formed → thiosulfate titre → moles of iodine → moles of oxidising agent → concentration

Ideal for A-level Chemistry, redox chemistry, volumetric analysis, practical skills and examination revision.

Free classroom resource from ACE Chemistry.