Starch Iodine Paper – Packs & Rolls

Quick Answer: Starch Iodine Paper, more usually called starch iodide paper, is test paper impregnated with starch and an iodide salt that turns blue-black when an oxidising agent converts the iodide to iodine; it gives a quick visual check for chlorine, nitrous acid, hypochlorite, peroxides and similar oxidisers, and is offered in packs and rolls.

The Chemistry Behind the Blue-Black Spot

Iodide ions are colourless, but many oxidising agents convert them to iodine. The free iodine immediately forms an intense blue-black complex with the starch in the paper, so even a small amount of oxidant gives a visible dark mark. Having both components on the strip is what makes this paper more sensitive than paper carrying iodide alone.

The most familiar classroom use is the test for chlorine gas: a moistened strip held at the mouth of a test tube turns blue-black as chlorine displaces iodine. In organic preparations the paper is used to judge the end of a diazotisation, where a drop of the reaction mixture giving an immediate dark mark shows that a slight excess of nitrous acid is present. It also serves to check for residual bleach or peroxide in cleaning and process rinse solutions.

The product title uses the name ‘starch iodine paper’. The paper that detects iodine directly is plain starch paper, whereas the reagent paper for oxidising agents is starch iodide paper, which is also the name in the product image filename. Buyers who need plain starch paper for iodine detection should mention it when enquiring.

Specifications

Applications

• Testing for chlorine gas in school and college gas-test practicals.
• Monitoring for excess nitrous acid during diazotisation in organic chemistry labs.
• Checking for residual hypochlorite or peroxide after cleaning or disinfection steps.
• Demonstrating redox reactions and the iodine-starch complex in class.

Storage and Handling

• Keep the paper closed and in the dark; light and air slowly oxidise iodide and darken unused strips.
• Store it away from bleach, chlorine-releasing disinfectants and nitric acid in the prep room.
• Carry out chlorine tests in a fume hood with very small quantities, moistening the strip with distilled water first.
• Discard strips that have turned grey or blue before use.

Why Choose LabEquip

Chemistry teachers stocking gas-test reagents, organic chemistry labs running diazotisations and quality staff checking disinfectant residues are the regular buyers. LabEquip lists this paper beside Potassium Iodide Paper in the General Lab Products range; packs or rolls can be chosen via the contact page to suit how often it is used.

Frequently Asked Questions

What does starch iodide paper test for?

It tests for oxidising agents. Chlorine, nitrous acid, hypochlorite, hydrogen peroxide and other oxidisers convert iodide to iodine, which forms a blue-black complex with the starch.

Is starch iodine paper the same thing?

The two names are often mixed up. The paper for detecting oxidising agents contains iodide and starch; plain starch paper is used to detect iodine itself. This listing is described as the iodide type.

Why must the paper be moistened for the chlorine test?

The reaction between chlorine and iodide takes place in solution. A film of distilled water on the paper lets the gas dissolve and react, giving a quick colour change.

How is the paper used during diazotisation?

A drop of the reaction mixture is spotted onto a strip. An immediate blue-black colour shows a slight excess of nitrous acid, meaning enough sodium nitrite has been added; no colour means more is needed.

Can the test give a false positive?

Yes. Any oxidising agent gives the same colour, and old paper exposed to air and light can darken on its own. Strong acid on the strip can also slowly release iodine, so read the result promptly.

Should I choose packs or rolls?

Packs of ready-cut strips suit classes where each student needs a few pieces. Rolls in a dispenser suit labs that tear off strips of any length for repeated testing.

Last Updated: September 2026