Chemical Reactions

AB + CD->CB + AD

Double Displacement

A double displacement reaction involves two reactants rearranging cations and ions to form two new compounds. This type of reaction usually occurs in aqueous solutions, so in order to predict the products, the solubility of the substances must be considered.

sodium sulfide(aq) + hydrochloric acid(aq)->sodium chloride(aq) + hydrogen sulfide (g)
Na2S(aq) + 2HCl(aq)->2NaCl(aq) + H2S(g)

Application

Sea water contains magnesium chloride, a soluble ionic compound. In the large-scale commerical preparation of magnesium, calcium hydroxide is added to large quantities of sewater, resulting in the production of magnesium hydroxide:srcmagnesium chloride(aq) + calcium hydroxide(aq)->magnesium hydroxide2(s) + calcium chloride (aq)
MgCl2(aq) + Ca(OH)2(aq)->Mg(OH)2(s) + CaCl2(aq)

Impact

If care is not taken with the sea water extraction, serious damage can be done to the environment. The greatest risk is the contamination of the sea water by the other chemicals used in the reaction, potentially killing some of the marine life in the area.