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Carbonate salts can be divided into three main categories: normal salts, acid salts, and basic salts. It generally refers to normal salts, with sodium carbonate Na2CO3, potassium carbonate K2CO3, ammonium carbonate (NH4)2CO3, calcium carbonate CaCO3, etc. being important ones. Carbonates of ammonium and alkali metals (except lithium carbonate, Li2CO3) are soluble in water. Alkali metal carbonates are strong bases and weak salts; in aqueous solution, the CO32- ions undergo hydrolysis, which gives them basic properties. Carbonates of other metals are insoluble in water, but they react when exposed to acids, even acetic acid, resulting in their dissolution and the release of carbon dioxide. Alkali metal carbonates, with the exception of Li2CO3, have high thermal stability and do not decompose easily when heated; ammonium carbonate decomposes upon heating to yield ammonia, carbon dioxide, and water, while carbonates of other metals decompose to form metal oxides and CO2. By introducing CO2 into an aqueous solution or suspension of carbonates, it can be converted into the corresponding acid salts. Acidic carbonates are also known as bicarbonates or hydrogen carbonates, such as calcium bicarbonate Ca(HCO3)2. Insoluble carbonates have corresponding bicarbonates with relatively high solubility, whereas the bicarbonates of soluble carbonates have relatively low solubility. For example, alkali metal bicarbonates have lower solubility than their corresponding carbonates, and this is because the HCO-3 ions in solution can form dimeric or polymeric ions through hydrogen bonding, thereby reducing solubility. When heated, bicarbonates first decompose into CO2 and carbonates; further heating of the carbonates then causes them to decompose into metal oxides and CO2. When a bicarbonate solution is acidified, CO2 is released; when alkali is added, a positive salt is formed. Therefore, it is a compound with amphoteric properties. There are different types of basic carbonates; common ones include copper basic carbonate Cu2(OH)2CO3 and lead basic carbonate Pb2(OH)2CO3, among others. Carbonates are widely distributed in nature; common examples include limestone, chalk, marble, and calcite. Their main component is CaCO3, with only differences in form. Almost all soils also contain CaCO3.