Group 2

• uses of Mg(OH)2 in medicine

  • as an antacid
  • to relieve indigestion
  • used to neutralise excess stomach acid
• why does calcium have a higher melting point than strontium?

  • positive ions are smaller, so there is stronger attraction between cations and delocalised electrons
• powdered Al increase surface area of reactants, why does this increase reaction rate?

  • there is increased surface contact
  • this increases the amount of collisions in a given time
• why a method of extracting strontium may be expensive:

  • the reaction requires a lot of heat
  • extraction requires electrolysis
  • its endothermic
• trend in first ionisation energy down group 2

  • decreases
  • atomic radius increases and there is more shielding
  • so attraction between nucleus and outer electron is weaker
• why is sulphuric acid not used to acidify BaCl2?

  it contains sulfate ions which would form a white precipitate
• why is BaSO4 used in medicine?

  because it is insoluble
• flue gas removal

  CaO + 2H2O + SO2 —> CaSO3 + 2H2O
• test for sulphate

  • add HCl and BaCl2
  • white precipitate is formed if sulfate present
• trend in solubility with group 2 compounds

  • hydroxides; increases
  • sulfates; decreases
• when Mg reacts with steam, MgO is formed and a bright light can be observed
• the bonding in Mg

  there is attraction between a lattice of Mg2+ ions and a sea of delocalised electrons
• test for sulphate ions

  • add HCl and BaCl2
  • if sulphate ions are present, white precipitate of BaSo4 is formed
• Mg(OH)2 is sparingly soluble
• adding dilute NaOH to MgCl2 and BaCl2

  • white ppt forms with MgCl2, because Mg(OH)2 is formed, which is insoluble
  • No ppt forms for BaCl2, Ba(OH)2 forms which is soluble