4.6 - Properties of Group 2 Compounds

• Oxides


  basic oxides: metal Oxides that react with water to form salts and mater
• general equation For reaction of oxides with water

  MO+ H2O →M(OH)2

  makes hydroxides that dissolve forming OH- ions so solution is alkaline
• properties of magnesium oxide

  white solid

  high melting point

  reacts slowly with water to form slightly soluble Mg(OH)2

  used as heat- resistant ceramic to line furnaces
• general equation for reaction of Oxides with dilute acid

  MO + 2HCl → MCl2+ H2O
• trend in solubility of hydroxides

  increases down the group so solutions become more strongly alkaline
• general equation for reaction of hydroxides with water

  M(OH)2 +H20 →M(OH)2
• general equation for reaction of hydroxides with dilute acids.

  M(OH)2 + 2HCI → MCI2 +2H2O
• magnesium hydroxide


  barely soluble in water

  ingredient in milk of magnesia - used as an antacid & laxative
• calcium hydroxide


  slightly soluble in water forming limewater (alkaline)

  used to test for carbon dioxide - calcium hydroxide reacts with carbon dioxide to form insoluble precipitate of calcium carbonate
• barium hydroxide


  most soluble

  used as alkali in chemical analysis - better than KOH& NaOH because it can't be contaminated by carbonates because barium Carbonate is insoluble in water
• properties of carbonates


  general formula: MCO3

  insoluble in water

  decompose by heating

  become more thermally stable down the group
• properties of nitrates


  general formula: M(NO3)2

  colourless crystalline solids

  very soluble in water

  decompose to oxide on heating

  become more thermally stable down the group
• properties of sulfates


  general formula: MSO4

  colourless solids

  solubility decreases down the group
• hydrated magnesium sulfate


  epsom salts - a laxative
• hydrated calcium sulfate


  occurs naturally as gypsum

  produced on a largescale by removing sulfur dioxide from gases of coal-fired power stations

  used to make Plaster of Paris by removing water through crystallisation
• uses of Plaster of Paris

  Make building plasters and plasterboard

  good mould because it expands slightly as it sets so fills all gaps
• barium sulfate


  occurs naturally as baryte

  toxic but insoluble so used in 'barium meals' to diagnose stomach disorders as it absorbs x-rays