Group 2 Compounds: Reactions

Group 2 oxides and hydroxides are bases. They are neutralised by acids to form a salt and water.For example: MgO + 2HCl ----> MgCl2 + H2O Ca(OH)2 + 2HCl ----> CaCl2 + 2H2O As these reactions with hydrochloric acid take place you will see the solid oxide or hydroxide dissolve.Group 2 OxidesThe Group 2 oxides react with water to form a solution of the metal hydroxide.MgO + H2O -----> Mg(OH)2The typical pH of these solutions is 10-12.Group 2 HydroxidesGroup 2 hydroxides dissolve in water to form alkaline solutions. Ca(OH)2 + aq ------> Ca2+ + 2OH-The solubility of the hydroxides in water increases down the group. The resulting solutions are also more alkaline. Mg(OH)2 is only slightly soluble in water. The resulting solution is dilute with a comparatively low OH- concentration. Ba(OH)2 is much more soluble in water than MG(OH)2, with a greater OH- concentration. The resulting solution is more alkaline than a solution of Mg(OH)2. Group 2 CarbonatesThe Group 2 carbonates are decomposed by heat, forming the metal oxide and carbon dioxide gas.MgCO3 -----> MgO + CO2This type of reaction is called thermal decomposition.The carbonates become more difficult to decompose with heat as you move down the group.Properties of Group 2 Elements and Their Compounds Group 2 elements become more reactive down the group Group 2 carbonates decompose at higher temperatures down the group Hydroxides become more soluble in water and the resulting solutions become more alkaline. Uses of Group 2 HydroxidesThe alkalinity of the Group 2 hydroxides is used to combat acidity. Two common examples are: Calcium hydroxide - used by farmers and gardeners as 'lime' to neutralise acid soils Magnesium hydroxide - is used in 'milk of magnesia' to relieve indigestion. It works by neutralising any excess acid in the stomach.

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