The products of the reaction between barium chloride (BaCl2) and sulphuric acid (H2SO4) are barium sulphate (BaSO4) and hydrochloric acid (HCl). This is known as a precipitation reaction, because barium sulphate is a compound that is insoluble in water.
By balancing the chemical equation between the reactants and the products, it can be shown that two molecules of hydrochloric acid and one molecule of barium sulphate are produced for every reacting molecule of barium chloride and every reacting molecule of sulphuric acid. The barium sulphate formed is a white crystalline solid. Barium sulphate, when suspended in water, is used as a radiocontrast agent in medical radiology.