Potassium chromate

Potassium chromate is the inorganic compound with the formula K₂CrO₄. This yellow solid is the potassium salt of the chromate anion. It is a common laboratory chemical, whereas sodium chromate is important industrially.

Structure

Two crystalline forms are known, both being very similar to the corresponding potassium sulfate. Orthorhombic β\-K₂CrO₄ is the common form, but it converts to an α-form above 666 °C (1,231 °F).^[1]

Production and reactions

It is prepared by treating potassium dichromate with potassium hydroxide:^{[citation needed]}

K₂Cr₂O₇(aq) + ₂ KOH → ₂ K₂CrO₄ + H₂O

Or with potassium carbonate:^[2]

K₂Cr₂O₇ + K₂CO₃ → ₂ K₂CrO₄ + CO₂

Or, the fusion of potassium hydroxide and chromium trioxide:^{[citation needed]}

₂ KOH + CrO₃ → K₂CrO₄ + H₂O

When treated with lead(II) nitrate, it gives an orange-yellow precipitate, lead(II) chromate.^{[citation needed]}

Applications

Unlike the less expensive sodium salt, the potassium salt is mainly used for laboratory work in situations where an anhydrous salt is required, or as an oxidizing agent in organic synthesis.^[1]

It is used in qualitative inorganic analysis, e.g. as a colorimetric test for silver ion. It is also used as an indicator in precipitation titrations with silver nitrate to measure levels of chloride ion (the Mohr method of determining chloride) since red silver chromate is precipitated in the presence of any excess of silver ions when potassium chromate is present. This titration proceeds by the following reactions, where silver nitrate is used as the titrant:^[3]

Ag+ + Cl- → AgCl

₂ Ag+ + CrO₄- → Ag₂CrO₄

Safety

As with other Cr(VI) compounds, potassium chromate is carcinogenic. Positive associations with lung cancer at a very high rate, and nasal / sinus cancer at a 100x lower rate than lung cancer have been found using worker exposure data. In general, less soluble chromates are a larger chronic hazard as they can be encapsulated in the lung without being absorbed and excreted, giving more time for reactive intermediates to be produced. Animal data indicates a potential for impaired fertility, heritable genetic damage and harm to unborn children, along with other types of cancer via less common exposure routes.^[4]

As a highly soluble hexavalent chromium compound, potassium chromate is also acutely toxic, though it is poorly absorbed from the intestinal tract.^[4] The compound is also corrosive and exposure may produce severe eye damage or blindness.^[5]

References

1. ^
2. ^ Fedoroff, Basil T. & Sheffield, Oliver E. (1 January 1966). "C - Chromates - Potassium Chromate". Encyclopedia of Explosives and Related Items. Vol. 3, Chlorides through Detonating Relays. Picatinny Arsenal, NJ: U.S. Army Armament Research Development And Engineering Center - TACOM, ARDEC - Warheads, Energetics And Combat Support Armaments Center. pp. C281–2. AD0653029, PATR 2700.
3. ^ Chloride, titrimetric, Mohr. National Environment Methods Index (NEMI). I-1183-85.
4. ^ Volume 100C: Arsenic, Metals, Fibres, and Dusts. Lyon, France: World Health Organization - International Agency for Research on Cancer. 2012. pp. 153–64. ISBN 978-92-832-0135-9. Retrieved 2020-01-05.
5. ^ "SDS - Potassium Chromate". fishersci.com. Thermo Fisher Scientific. 29 March 2024. Retrieved 31 October 2025.