Acids and Alkalis: Reaction of Acids

Acids can react with a range of substances including metals, bases, alkalis and carbonates.
The reaction of an acid with a metal produces a salt and hydrogen gas. This is an example of a redox reaction where the metal is oxidised and the hydrogen ion in the acid is reduced.
The general formula for a reaction of an acid with a metal can be represented as: Acid + Metal → Salt + Hydrogen gas
Bases are substances that can react with acids to form salts and water. This type of reaction is called a neutralisation reaction. Alkalis are bases that are soluble in water.
The formula for the reaction of an acid with a base is: Acid + Base → Salt + Water
Alkalis such as sodium hydroxide (NaOH) or potassium hydroxide (KOH) can react with acids in a similar way to form salts and water.
The reaction of an acid with a carbonate also produces a salt, but in addition it produces water and carbon dioxide.
The formula for the reaction of an acid with a carbonate can be represented as: Acid + Carbonate → Salt + Water + Carbon dioxide
The reactions of acids are exothermic, which means they give out heat. When acids react with alkalis in a solution, the solution’s temperature rises.
pH is a measure of the hydrogen ion concentration in a solution. Acids have a pH less than 7, alkalis have a pH greater than 7 and neutral substances have a pH of 7. A change in pH can indicate a chemical reaction has occurred.
Indicators, such as litmus paper, can help determine whether a solution is an acid or an alkali. Acids turn litmus paper red, while alkalis turn it blue. Universal indicator or pH meters can be used to determine the exact pH of a solution.