Potassium chloride

Potassium chloride, also known as KCl or potassium salt, is a chemical compound made from potassium and chlorine. It looks like a white or clear crystal and has no smell. You can dissolve it in water, and it tastes like salt.

People use potassium chloride in many ways. It can replace regular table salt for people who need to watch their sodium intake. It is also used in farming to help plants grow, in medicines, and in devices that soften water at home. You might find it in food processing too, where it is listed as additive E508.

Potassium chloride is found naturally in a mineral called sylvite, named after an old name for the salt. It also appears together with sodium chloride in a mineral called sylvinite.

Uses

Fertilizer

Most potassium chloride is used to make fertilizer, also called potash, because plants need potassium to grow well. Potassium chloride used in farms is known as muriate of potash. It has a lot of potassium and is cheaper than other potassium sources. Potassium is very important for plants—it helps them make food, use water, and stay healthy.

Medical use

Our bodies need potassium to work properly. Potassium chloride taken by mouth is used to treat low levels of potassium in the blood. It is also used in special drinks to help people who have lost fluids due to sickness. Too much potassium chloride can be harmful and may affect the heart.

Culinary use

Potassium chloride can be used instead of regular table salt in food. However, some people find it tastes bitter, so it is often mixed with regular salt to make it taste better. Health guidelines suggest using lower-sodium salt substitutes for adults to help them eat less salt, but these are not recommended for children or people with certain health conditions.

Industrial

In the past, about 5% of potassium chloride was used to make other chemicals, such as potassium hydroxide and chlorine.

Niche and archaic

Potassium chloride has a few special uses. It can be added to animal food to give animals more potassium, which can also help animals produce more milk. It is sometimes used in oil and gas work, and in water softeners at home. It can also be used to check radiation measuring tools and in some types of fire extinguishers. It was once used in old television screens and for welding aluminium, but these uses are rare today.

Toxicity

Potassium chloride is safe when eaten in small amounts, like what is normally in food. But if someone eats a lot of it, it can be harmful.

For example, it would take about 190 grams of potassium chloride for a person who weighs 75 kilograms to feel serious effects if taken by mouth. This is more than the amount of table salt a person would need to feel similar effects. If put directly into a vein, even a much smaller amount can be dangerous.

Chemical properties

KCl can dissolve in many polar liquids.

Mixes of KCl are often used to check the electrical conductivity of ionic liquids because KCl mixes stay the same, helping scientists make exact measurements. When mixed with water, KCl separates completely into K⁺ and Cl⁻ bits.

Potassium is more willing to give away electrons than sodium, but KCl can be turned into potassium metal by mixing it with sodium metal at very high heat, around 850 °C. The potassium, which turns into gas more easily, can be taken away by heating, following Le Chatelier's principle:

KCl_(l) + Na_(l) ⇌ NaCl_(l) + K_(g)

This is the main way to make potassium metal. Trying to use electrolysis does not work because potassium mixes too well with melted KCl.

Scientists think that other mixes of potassium chloride might become stable under very high pressure, over 20 GPa. They have made and studied two types of KCl₃. Between 20-40 GPa, it forms a special shape with K⁺ and Cl₃⁻ bits; above 40 GPa, it changes into a shape like the metal mix Cr₃Si.

Physical properties

Potassium chloride has a crystal structure similar to table salt, forming a face-centered cubic shape. It can break easily in three directions. When heated, it can change shape under high pressure.

Some of its important properties include how well it lets light pass through, how much it bends light, and how well it conducts heat. When potassium chloride is powdered and put in a flame, it gives off a lilac color.

Production

Potassium chloride comes from minerals such as sylvite, carnallite, and potash. It can also be taken from salt water or made through special processes like flotation or electrostatic separation. Some potassium chloride is made when nitric acid is produced from potassium nitrate and hydrochloric acid.

Most potassium chloride is made for farms and industries in places like Saskatchewan, Canada, Russia, and Belarus. In 2017, Saskatchewan alone made more than a quarter of all the potash in the world.

Laboratory methods

Potassium chloride is easy to buy, so it is not usually made in a lab. But it can be created by mixing potassium hydroxide with hydrochloric acid:

KOH + HCl → KCl + H₂O

This is a type of acid-base neutralization reaction. The salt can then be cleaned by recrystallization. Another way is to let potassium burn with chlorine gas, which creates a lot of heat:

2 K + Cl₂ → 2 KCl