Module 3.1.2- Group 2

    Cards (12)

    • Reducing agent
      electron donor reducing another species
    • Example of group 2 element being oxidised
      Ca -> Ca2+ + 2e-
      [Ar]4s2 -> [Ar]
    • Redox reactions with oxygen (group 2)

      Group 2 elements all react with oxygen to form metal oxide
      2Mg + O2 -> 2MgO
      Mg is oxidised
      O is reduced
    • Redox reactions with water (group 2)
      Group 2 elements reacts with water to form alkaline hydroxide and hydrogen.
      reactivity increases down the group
      Sr + 2H2O -> Sr(OH)2 + H2
      Sr is oxidised
    • Redox reactions with dilute acids (Group 2)
      metal + acid -> salt and hydrogen
      Mg is oxidised
      H is reduced
    • Trend in reactivity and IE for group 2
      Dependent on the first and second ionisation energy.
      As you go down the group, IE decreases due to increasing atomic radius and increasing shielding therefore it is easier to remove an electron increasing reactivity.
    • Group 2 oxides with water
      the oxides of group 2 elements react with water to form alkaline solutions of the metal hydroxides.
      hydroxide ions are released, OH-, which make the solutions strongly alkaline.
      CaO (s) + H₂O (l) → Ca(OH)₂ (aq)
      CaO (s) + H₂O (l) → Ca²⁺ (aq) + 2OHˉ (aq)
      the group 2 hydroxides are only slightly soluble in water. when the solution becomes saturated, any further metal & hydroxide ions will form a solid precipitate
      Ca²⁺ (aq) + 2OHˉ (aq) → Ca(OH)₂ (s)
    • What happens to the solubility of hydroxides as you go down Group 2
      Increases as you go down so resulting solutions contain more OH- ions and are more alkaline (pH increases)
    • Trend in alkalinity down group 2
      increases
    • Experiment to show trend of alkalinity down group 2

      1) add each group 2 oxide to water
      2) shake.
      on this scale, there is insufficient water to dissolve all of the metal hydroxide that forms. there will be a saturated solution of each metal hydroxide with some white solid undissolved at the bottom of the test-tube.
      3) measure pH of each solution
    • Use of Ca(OH)2
      Used in agriculture
      Neutralises acid soils by increasing pH (important as plant growth depends on soil pH - improve yield)
    • Use of Mg(OH)2 or CaCO3
      To treat constipation and neutralise excess stomach acid
      HCl (acid indigestion)safe as it is weakly alkaline
      Mg(OH)2 + 2HCl -> MgCl2 + 2H2O
      CaCO3 + 2HCl -> CaCl2 + H2O + CO2