Potassium Iodide Paper

Quick Answer: Potassium Iodide Paper is test paper treated with potassium iodide; when it meets an oxidising agent such as chlorine, bromine or ozone, the iodide is oxidised to iodine and the paper turns yellow to brown, giving a simple visual test for oxidants.

Iodide Alone Versus Iodide With Starch

The reaction is the one used in iodometric titrations: an oxidant takes electrons from iodide ions and releases free iodine. On plain iodide paper that iodine shows as a yellow-brown stain whose depth grows with the amount of oxidant. When starch is also present, the same iodine forms a far darker blue-black complex that is easier to see at low levels.

Plain iodide paper is therefore less sensitive than Starch Iodide Paper, but it has uses of its own. Its brown colour remains readable where a starch complex would be masked, and it shows the halogen displacement series simply: chlorine water and bromine water both release iodine from iodide, demonstrating that they are stronger oxidising agents than iodine.

Papers labelled ‘potassium iodide starch paper’ are sold under similar names, so whether this listing’s paper carries starch is worth checking if sensitivity matters for your work.

Applications

• Halogen displacement practicals showing that chlorine and bromine oxidise iodide.
• Detecting chlorine or bromine vapour escaping from a reaction vessel.
• Rough checks for oxidising residues, such as hypochlorite, in rinse water.
• Explaining the chemistry of iodometric titrations before students carry them out.

Care & Handling

• Keep the strips sealed and in the dark; unused paper slowly yellows as air oxidises the iodide.
• Store them away from chlorine-releasing chemicals and oxidising acids.
• Compare a test strip with an unused strip from the same batch when judging a faint colour.

Specifications

Why Choose LabEquip

Teachers preparing halogen chemistry practicals and labs needing a quick oxidant check are the usual buyers of potassium iodide paper. LabEquip supplies it with the rest of its test papers under General Lab Products, and the required format can be agreed through our contact page.

Frequently Asked Questions

What colour does the paper turn with an oxidising agent?

It turns yellow to brown as iodine is released, and the colour deepens with more oxidant. A large excess of chlorine can fade it again by oxidising the iodine further.

How is it different from starch iodide paper?

Starch iodide paper also contains starch, which turns blue-black with iodine and makes the test more sensitive. Plain iodide paper shows a yellow-brown colour and needs more oxidant to give a clear result.

Does this paper contain starch?

The listing names potassium iodide only, and some products with similar names also carry starch. If you need the starch version for low-level detection, ask for it when enquiring.

Can potassium iodide paper test for chlorine gas?

Yes. Moisten the strip with distilled water and hold it near the gas; it turns brown as chlorine releases iodine. Work in a fume hood, since chlorine is toxic.

Why does unused paper turn yellow over time?

Oxygen in the air, helped by light and acid fumes, slowly oxidises iodide to iodine. Keeping the paper sealed, dry and dark slows this down.

Can the paper measure the amount of oxidant?

Only roughly, by comparing the depth of colour. For quantitative results, an iodometric titration with sodium thiosulfate is used instead.

Last Updated: September 2026