- What it is. This potassium iodide is supplied as ACS reagent-grade white crystals in a 500 g size. It is the standard iodide salt for iodometric titrations, reagent preparation, and analytical chemistry.
- What ACS grade guarantees. ACS reagent potassium iodide assays at 99.0% minimum, with limits on iodate (3 ppm), chloride and bromide (0.01%), sulfate (0.005%), phosphate (0.001%), heavy metals (5 ppm), iron (3 ppm), and alkali and alkaline earth metals. A 5% solution has a pH of 6.0-9.2.
- Why iodate matters. Iodate reacts with iodide in acid to release iodine, which would add a false signal in iodometric titrations. The tight iodate limit in ACS grade keeps blank values low and results accurate.
- Chemical identity. Potassium iodide (CAS 7681-11-0, KI, 166.00 g/mol) is a white crystalline salt that melts at about 681 °C and has a density of about 3.13 g/cm³. It dissolves readily in water and moderately in alcohol.
- Iodometric chemistry. Dissolved iodide reacts with oxidizing agents to release iodine, which is titrated with standard sodium thiosulfate. Potassium iodide also dissolves iodine as triiodide, which is how standard iodine solutions are prepared.
- Other laboratory uses. Potassium iodide is used to prepare starch-iodide test papers, Lugol's iodine, Nessler's reagent, and iodide standards, as a precipitating agent for silver and lead, and in organic synthesis as a source of iodide.
- Preparing standard iodine solutions. Iodine dissolves poorly in water alone, but it dissolves readily in potassium iodide solution as the triiodide ion. Therefore, standard iodine titrants are prepared by dissolving iodine in concentrated potassium iodide and diluting to volume.
- Stability and storage. The crystals slowly yellow in moist air and light as traces of iodine form. Keep the container tightly closed, dry, and protected from light to preserve purity.
- Handling at a glance. Potassium iodide can irritate the eyes and skin, and repeated or prolonged exposure can affect the thyroid. Wear safety glasses and gloves and avoid creating dust. For a ready-made solution, see Lab Pro's Potassium Iodide 10% (w/v) Solution, 1 Quart.
Technical Specifications
| Chemical Name | Potassium iodide |
| CAS Number | 7681-11-0 |
| EC Number | 231-659-4 |
| Synonyms | Kali iodide, KI |
| Formula | KI |
| Molecular Weight | 166.00 g/mol |
| Grade | ACS reagent |
| Assay | 99.0% min |
| pH (5% solution, 25 °C) | 6.0 to 9.2 |
| Insoluble Matter | 0.005% max |
| Loss on Drying (150 °C) | 0.2% max |
| Iodate (IO3) | 3 ppm max |
| Chloride and Bromide (as Cl) | 0.01% max |
| Sulfate (SO4) | 0.005% max |
| Phosphate (PO4) | 0.001% max |
| Barium (Ba) | 0.002% max |
| Calcium (Ca) | 0.002% max |
| Magnesium (Mg) | 0.001% max |
| Sodium (Na) | 0.005% max |
| Heavy Metals (as Pb) | 5 ppm max |
| Iron (Fe) | 3 ppm max |
| Melting Point | About 681 °C |
| Density | About 3.13 g/cm³ |
| Form | White crystals |
| Package Size | 500 g |
Applications / Common Uses
- Iodometric titrations: Supplies iodide for oxidant determinations.
- Iodine solutions: Dissolves iodine as triiodide.
- Reagent preparation: Prepares Lugol's, Nessler's, and starch-iodide reagents.
- Precipitation: Precipitates silver and lead as iodides.
- Organic synthesis: Provides iodide for substitution reactions.
Storage, Handling & Shipping
Store tightly closed in a cool, dry place protected from light and moisture, away from strong oxidizers and acids. Moist air and light slowly release traces of iodine, so reseal the container promptly after use.
- Incompatible materials: Strong oxidizers, strong acids, and metal salts that form insoluble iodides.
- Personal protection: Safety glasses, gloves, and dust control.
- Spill response: Sweep up without raising dust and place in a closed container for disposal.
- First aid: Eyes: rinse with water for several minutes. Ingestion: seek medical advice.
Related Categories & Services
- Shop ACS Grade Laboratory Chemicals for related products in this category.
- Explore Inorganic Chemicals and Buffers, Standards & Solutions.
- Vendor Managed Inventory (VMI) Program: Lab Pro can stock, track, and replenish this item on site so it never runs out. Contact info@labproinc.com or 888-452-2776 to set up a VMI assessment.
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FAQs
What is ACS grade potassium iodide used for?
It is used in iodometric titrations to measure oxidizing agents, to prepare standard iodine solutions, Lugol's iodine, Nessler's reagent, and starch-iodide papers, as a precipitating agent, and in organic synthesis. ACS grade limits impurities such as iodate that would bias analytical results. It is a staple reagent in water labs.
Why is low iodate important in potassium iodide?
Iodate reacts with iodide in acid to form iodine, which would be counted as if it came from the sample. ACS grade limits iodate to 3 ppm, which keeps reagent blanks low and ensures that iodometric titration results reflect only the analyte. Check each lot certificate for iodate.
Why does potassium iodide turn yellow?
In moist air and light, small amounts of iodide oxidize to iodine, which gives the crystals a yellow tint. Keep the container tightly closed, dry, and away from light. Discolored material may raise blank values in sensitive iodometric work. Buy a size you can use while fresh to limit discoloration.
How do I make a 10% potassium iodide solution?
Dissolve 100 g of potassium iodide in deionized water and dilute to 1 liter. For oxygen-sensitive methods, use freshly boiled and cooled water. Store the solution in a dark place and prepare it fresh if it turns noticeably yellow. Label the solution with its preparation date.
Is potassium iodide hazardous?
Potassium iodide can irritate the eyes and skin, and repeated or prolonged exposure may affect the thyroid. Wear safety glasses and gloves, avoid creating dust, and do not ingest it. Review the safety data sheet for the exact classification before use. Keep it away from food areas.
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