Carbonate

A carbonate is a type of chemical that comes from carbonic acid. It has a special group of atoms called the carbonate ion, with the formula CO₃^2–.

Carbonates are found in many everyday things, like fizzy drinks. In drinks, carbonates mean adding carbon dioxide to water to make it bubbly. This is called carbonation.

In nature, carbonates are very important. They are in many rocks and minerals. A common carbonate is calcite, which is mostly calcium carbonate. This mineral is a big part of limestone, the rock that makes up many hills and mountains. It also forms the shells of molluscs and the skeletons of corals in the ocean.

People have used carbonates for thousands of years. For example, sodium carbonate, also called soda or natron, was used for cleaning long ago. Today, carbonates are used to make glass, cement, and special batteries called molten carbonate fuel cells. They are useful in many parts of industry and science.

Structure and bonding

The carbonate ion is made of one carbon atom and three oxygen atoms in a flat triangle. It has a mass of 60.01 g/mol and a charge of −2. It is linked to the hydrogencarbonate ion, which comes from carbonic acid.

The bonds between the carbon and oxygen atoms share their length in a process called resonance. This makes all three bonds look the same. This is similar to what happens with the nitrate ion.

Chemical properties

Metal carbonates break down when heated. They release carbon dioxide and leave behind a metal oxide. This process is called calcination. For example, calcium carbonate becomes calcium oxide and carbon dioxide.

Carbonate can connect to many metal ions. Some carbonates, like those of lithium, sodium, and potassium, dissolve in water. Others, like calcium carbonate, do not. Calcium carbonate can build up in pipes, which is why hard water often needs treatment. When acid is added to carbonates, carbon dioxide gas is released. This is why acid can remove limescale buildup.

Organic carbonates

In organic chemistry, a carbonate is a special part inside a bigger molecule. This part has a carbon atom connected to three oxygen atoms. One oxygen is connected very strongly to the carbon. These are called organocarbonates or carbonate esters. Some important ones are dimethyl carbonate, and cyclic compounds like ethylene carbonate and propylene carbonate.

Buffer

Our blood has a special system that helps keep its pH just right, like a buffer. This system uses three important reactions with carbonates. When we breathe out carbon dioxide, it changes how these reactions work, helping to keep the blood balanced.

The same kind of buffer system is also important in the oceans. It affects our climate and the carbon cycle because many sea creatures, like corals, are made of calcium carbonate. When the ocean gets warmer, it can dissolve more carbonate, which can change the amount of carbon dioxide in the air and affect Earth’s temperature.

Carbonate salts

Carbonates are salts made from carbonic acid. They contain a special group of atoms called the carbonate ion, with the formula CO₃^2–. You can find these salts in rocks and minerals.

We also use the word "carbonate" when we add carbon dioxide to water. This makes fizzy drinks. It also increases the amount of carbonate and bicarbonate ions in the water.

Presence outside Earth

Carbonates in rocks can show that there was liquid water. Scientists have found carbonates in space, in a planetary nebula called NGC 6302, even though water may not be there like on Earth.

Small amounts of carbonate have been found on Mars using special cameras and in rocks from Mars that fell to Earth. There might have been water in places like Gusev and Meridiani Planum on Mars.