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A-LEVEL NOTES

A-LEVEL AQA ChEMISTRY NOTES 
group 2, the alkaline earth metals


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Group 2, Alkaline Earth Metals
  • All Group 2 elements have 2 electrons in their outer s-subshell.
  • Down the group ionisation energy decreases, as the atomic radius and shielding increases, decreasing the attraction of the electron to the nucleus
  • Melting point also decrease down the group due to the increased atomic radii and shielding, so metallic bonding is weaker
  • Group 2 elements react with water to form hydroxides and hydrogen gas
                                  Mg (s) + 2H2O(l) → Mg(OH)2 (aq) + H2 (g)
Oxidation numbers:    0               +1                   +2                     0
  • Magnesium can also react with steam
                                   Mg (s) + H2O (g) → MgO (s) + H2 (g)
Oxidation numbers:   0            +1              +2             0

Group 2 
​Element
Group 2
​Hyroxide
Solubility of Hydroxide
Mg
Mg(OH)2
Slightly soluble
Ca
Ca(OH)2
Sparingly soluble
Sr
Sr(OH)2
​More soluble than Mg(OH)2 and Ca(OH)2
Ba
Ba(OH)2
Most soluble
  • Mg(OH)2 (milk of magnesia) is used to neutralise excess hydrochloric acid in the stomach, relieving indigestion
  • Titanium oxide reacts with carbon and chlorine to form titanium chloride, which is purified by fractional distillation and then reduced to titanium using magnesium
    • TiCl4(l)+ 2Mg(s)→ 2MgCl2 (s) + Ti (s)
  • Ca(OH)2 (hydrated lime) is used to neutralise acidic soil
  • CaO and CaCO3 can be used to remove SO3 from flue gases
CaO (s) + 2H2O (l) + SO2 (g) → CaSO3 (s) + 2H2O (l)
CaCO3 (s) + 2H2O (l) + SO2 (g) → CaSO3 (s) + 2H2O (l) + CO2 (g)
Group 2 Element
Group 2 Sulphate
Solubility of Sulphate
Mg
MgSO4
Soluble
Ca
CaSO4
Slightly soluble
Sr
SrSO4
Insoluble
Ba
BaSO4
Insoluble
  • BaSO4 can be ingested to visual soft tissue in imaging
  • Acidified BaCl2 can be used to test for the presence of sulphate ions as barium sulphate, a white precipitate, will be formed. The solution needs to be acidified to remove any sulphites or carbonates, which would result in the formation of a white precipitate
Ba^2+ (aq) + SO4^2+(aq) → BaSO4(s) ​
​

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