Question

What are carbonate ions and how can you recognize them?

Answer 1

As we know that the carbonates are the classes of chemical compounds that are derived from carbonic acid and carbon dioxide. The carbonate ion consists of one carbon atom which is surrounded by three oxygen atoms.

Complete answer:

As we know that carbonate ions are formed of a carbon atom and three oxygen atoms and are generally negative species.
We are already aware that carbonates are derived from carbonic acid as well as from carbon dioxide. The carbonic acid consists of carbonate ions and hydrogen ions. We can show the dissociation of carbonic acid as:
${H_2}C{O_3} \rightleftharpoons 2{H^ + } + CO_3^{2 - }$
These carbonate ions are generally associated with metal ions and some are soluble in water. These ions may result in precipitates and aqueous carbonate ions.
Now, there are some tests to recognise the carbonate ions present in the organic and inorganic salts. We know that carbonate ions can be solids and solid metal carbonate compounds easily react with dilute acids and result in carbon dioxide release. For instance, calcium carbonate when reacted with hydrochloric acid, it results in the formation of calcium chloride, carbon dioxide and water which we can show with the help of a given chemical equation.
$CaC{O_3} + 2HCl \to CaC{l_2} + C{O_2} + {H_2}O$
Some metal carbonates are insoluble in water like lithium carbonate and all alkali earth metals along with transition metals. We should know that carbonates which are insoluble in water or acidic solutions generally are found to form white precipitates in the solution. For example: Barium carbonate generally gives off white precipitate while dissolved in acidic solution which indicates the presence of carbonate ions in the salt.

Note: We can also recognise carbonate in phenolphthalein because it gives a pink colour in the presence of carbonate ions whereas hydrogen carbonate gives off a colourless solution of phenolphthalein. Also remember that the pH of carbonate solutions are generally higher than 7 indicating that they are weak bases. Carbonate ions decomposition always results in carbon dioxide gas release.