Group 2 Compounds (OCR A Level Chemistry)

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Group 2 Oxides & Water

  • Group 2 oxides react with water, releasing hydroxide ions, to form alkaline solutions:
CaO (s) + H2O (l) → Ca2+ (aq) + 2OH(aq)

  • These solutions get more alkaline going down the group
    • This is due to increasing solubility meaning the resulting solutions formed contain more OHions
  • When the solution becomes saturated any further metal and hydroxide ions will form a precipitate:
 Ca2+ (aq) + 2OH(aq) → Ca(OH)(s)

  • Solid magnesium hydroxide, Mg(OH)(s), is only slightly soluble in water
    • The solution has a low OH-(aq) concentration and a pH ≅ 10
  • Barium hydroxide, Ba(OH)(s), is much more soluble in water
    • The solution has a greater OH-(aq) concentration and a pH ≅ 13

Uses of Group 2 Compounds

  • Due to their basic properties and ability to neutralise acids, Group 2 oxides, hydroxides and carbonates have many uses

Group 2 compounds in agriculture

  • Calcium hydroxide, Ca(OH)2, is reasonably soluble in water and is used in agriculture to neutralise acidic soils
Ca(OH)(s) + 2H(aq) → Ca2+ (aq) + 2H2O (l)

  • It is important to regulate how much is added as If too much is added then this will result in soil becoming too alkaline to sustain crop growth

Group 2 compounds in medicine

  • Magnesium hydroxide, Mg(OH)2, is partially soluble in water and is used in suspension (known as 'milk of magnesia') to neutralise excess acid in the stomach and treat constipation
Mg(OH)(s) + 2HCl (aq) → MgCl(aq) + 2H2O (l)

  • It is safe to use as the magnesium hydroxide is only partially soluble making the solution only slightly alkaline (pH ≅ 10) due to the low OH- concentration

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Sonny

Author: Sonny

Expertise: Chemistry

Sonny graduated from Imperial College London with a first-class degree in Biomedical Engineering. Turning from engineering to education, he has now been a science tutor working in the UK for several years. Sonny enjoys sharing his passion for science and producing engaging educational materials that help students reach their goals.