Potassium chloride

K 1
Cl 1

Formula unit Lattice

Choose Lattice to see one unit cell. Then drag to rotate; pinch or Ctrl + scroll to zoom. Arrow keys rotate, + − zoom, R resets.

2 atoms in one formula unit of an ionic lattice.

The drawing shows one formula unit of an ionic lattice, not a molecule; potassium chloride has no molecular shape.

IUPAC name: potassium chloride
Molar mass: 74.548(11) g/mol
Atoms: 2
SMILES: [Cl-].[K+]
InChIKey: WCUXLLCKKVVCTQ-UHFFFAOYSA-M
PubChem CID: 4873

Made of

K Cl

An ingredient list may call potassium chloride “potassium salt”, under guidance the US Food and Drug Administration (FDA) issued in December 2020. The name is meant to tell shoppers that it is a salt substitute. The resemblance runs to taste. It tastes similar to sodium chloride, according to Haz-Map, and HSDB, the Hazardous Substances Data Bank, records a strong saline taste.

ChEBI (Chemical Entities of Biological Interest) classes it as a metal chloride salt with K⁺ as the counterion, the positive ion balancing the chloride’s charge. Potassium and chlorine supply one ion each, for a molar mass of 74.55 g/mol. It melts at 771 °C on HSDB’s figure, or 770 to 773 °C in the International Chemical Safety Cards (ICSC). The crystals are hygroscopic, taking up water from the air, according to CAMEO Chemicals and the ICSC; HSDB describes them as nonhygroscopic.

Structure and bonding

One K⁺ ion and one Cl⁻ ion stand apart in the Formula unit drawing, with no bond between them. The pair is one formula unit of the lattice, a one-to-one ratio rather than a pair that could be lifted out of the crystal. The chemical bonding article explains why an ionic solid holds no molecules.

A thin outline marks the cube of one unit cell when the model switches to Lattice, and it holds four potassium ions and four chloride ions. Each ion has six neighbours of the opposite charge, all 3.14 Å away, and Coordination highlights one chloride ion among its six. These counts match the sodium chloride model’s, while the 3.14 Å spacing is this crystal’s own. No potassium ion has a chloride partner of its own: six sit around it at the same distance.

The crystals themselves are cubic: CAMEO Chemicals describes white to colourless cubes, and HSDB lists cubic crystals.

Where it turns up

Underground, potassium chloride is the mineral sylvite, also called sylvine. HSDB describes natural sylvite as opalescent or milky white, often tinted red by hematite. It rates 2 on the Mohs scale of hardness, which ranks minerals by which scratches which. Most production comes from solid ore lying 300 to 1700 m below ground. Below about 1100 m, solution mining takes over: the ore is dissolved in place and pumped up as brine. Solar evaporation of natural brines yields only about 3 per cent of world output.

Sylvite is mined in Saskatchewan, HSDB notes, and the US Environmental Protection Agency (EPA) places one of the largest potash deposits there. Separated from the mined minerals, it also reaches food: the US federal rule for the ingredient, 21 CFR 184.1622, permits it in infant formula. Its status as generally recognised as safe (GRAS) was affirmed in 1983.

Why it matters

Fertilisers take more than 90 per cent of all potassium chloride made, HSDB reports, in single- or multi-nutrient products, used as it is or turned first into potassium sulfate. Potassium, in the EPA’s words, is a vital nutrient for crops, one that does much to decide their yields. In 2018 the US Department of the Interior added potash to its list of critical minerals. About 5 per cent of world output serves as an industrial chemical, mostly to make potassium hydroxide and chlorine.

In food, the same federal rule lists it as a flavour enhancer, flavouring agent, nutrient supplement, pH control agent, stabiliser and thickener. Other uses, according to HSDB, include water softening, drilling mud for oil wells, electroplating of metals, heat treatment of steel, recycling of aluminium, and melting snow and ice. It also has places in photography, in buffer solutions and in electrode cells. ChEBI lists it as a reference compound in nuclear magnetic resonance (NMR) spectroscopy: a standard against which the positions of other signals, their chemical shifts, are measured.

Properties

Properties of potassium chloride Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 4873.
Property	Value	Unit	Source
Formula (Hill order)	ClK
Molar mass	74.548(11) g/mol	g/mol	IUPAC/CIAAW 2024
Potassium atoms	1
Chlorine atoms	1
PubChem molecular weight	74.55 g/mol	g/mol	PubChem

Safety

Everyday uses of potassium chloride, as fertiliser, food ingredient and salt substitute, carry essentially no hazard. Of 875 reports under the Globally Harmonized System (GHS), 94.3% found it met no hazard criteria, and the EPA’s Safer Choice programme rates it of verified low concern. The ICSC still records that it irritates the eyes and the respiratory tract. The PubChem Laboratory Chemical Safety Summary for potassium chloride lists the full classification.

Questions

Why is potassium chloride used as a salt substitute?

In the FDA's view, sodium chloride and potassium chloride have, to a certain extent, a similar taste and do similar jobs in food, such as preserving it and keeping it moist. In most products potassium chloride replaces only part of the salt rather than all of it. The agency also notes that the US population eats too much sodium and too little potassium.

Which liquids dissolve potassium chloride?

Water does: HSDB gives 35.5 g dissolving in 100 g of water at 25 °C. Ether and acetone leave it undissolved, on HSDB's data, and Chem1 notes that most solvents other than water fail to dissolve ionic solids. Hydrochloric acid, sodium chloride or magnesium chloride already in the water lowers its solubility.

Is potassium chloride a medicine?

Yes. MeSH, the Medical Subject Headings vocabulary, describes its use to replenish electrolytes and restore the body's water-electrolyte balance in hypokalaemia, an abnormally low level of potassium in the blood. The World Health Organization includes it in its Model Lists of Essential Medicines. Chloride, its anion, has a separate job in the blood: in red cells carrying carbon dioxide it is exchanged for bicarbonate, the chloride shift, which keeps the charges balanced.