Making Salts

Making Salts

  • Salts are ionic compounds produced when an acid reacts with a base or an alkali.
  • The general equation for this reaction is acid + base → salt + water. This is a type of neutralisation reaction.
  • There are three main types of reactions used to make salts: acid-base reactions, acid-carbonate reactions, and acid-metal reactions.

Acid-Base Reactions

  • The base can be a metal hydroxide, oxide or ammonia.
  • For example, when hydrochloric acid reacts with sodium hydroxide, the salt sodium chloride is formed. The balanced equation is: HCl + NaOH → NaCl + H2O
  • If the base is insoluble, the reaction is done as a ‘titration’ where a soluble base (usually an alkali) is added to the acid until it is neutralised.

Acid-Carbonate Reactions

  • Carbonates react with acids to produce a salt, water, and carbon dioxide.
  • For example, the reaction of hydrochloric acid with sodium carbonate produces the salt sodium chloride, water, and carbon dioxide. The balanced equation is: 2HCl + Na2CO3 → 2NaCl + H2O + CO2

Acid-Metal Reactions

  • Most metals react with acids to form a salt and hydrogen.
  • For example, magnesium reacts with hydrochloric acid to form magnesium chloride and hydrogen. The balanced chemical equation is: Mg + 2HCl → MgCl2 + H2
  • This method is not suitable for metals above hydrogen in the reactivity series or for bases that do not contain a metal.

Crystallisation to Extract Salt

  • In all methods, the water can then be evaporated off to leave the salt crystals behind.
  • This could be done by gentle heating (i.e., using a water bath or an oven) or simply leaving the solution in a warm place to evaporate naturally.
  • Once the crystals are formed, they can be separated from the solution by filtration and then dried.

Remember that understanding the methods of making salts and the concept of neutralisation reaction could help in deducing the type of reactions and predicting the products involved.