Reactions of Group 2 (Edexcel AS Chemistry)

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Group 2 Elements

Reactions with water and oxygen

  • The reaction of group 2 metals with oxygen follows the following general equation:

2M (s) + O2 (g) → 2MO (s)

Where M is any metal in group 2

Remember than Sr and Ba also form a peroxide, MO2

  • The reaction of all metals with water follows the following general equation:

M (s) + 2H2O (l) → M(OH)2 (s) + H2 (g)

Except for, Be which does not react with water

Group 2 Metals reacting with Water and with Oxygen - Equations

  Reaction with oxygen Reaction with water
Mg 2Mg (s) + O2 (g) → 2MgO (s) Mg (s) + H2O (g) → MgO (s) + H2 (g) 
Ca 2 Ca (s) + O2 (g) → 2CaO (s) Ca (s) + 2H2O (l) → Ca(OH)2 (s) + H2 (g) 
Sr

2Sr (s) + O2 (g) → 2SrO (s)

Sr (s) + O2 (g) → SrO2 (s)

Sr (s) + 2H2O (l) → Sr(OH)2 (aq) + H2 (g) 
Ba

2Ba (s) + O2 (g) → 2BaO (s)

Ba (s) + O2 (g) → BaO2 (s)

Ba (s) + 2H2O (l) → Ba(OH)2 (aq) + H2 (g) 

  • Magnesium reacts extremely slowly with cold water:

Mg (s) + 2H2O (l) → Mg(OH)2 (aq) + H2 (g)

  • The solution formed is weakly alkaline (pH 9-10) as magnesium hydroxide is only slightly soluble
  • However, when magnesium is heated in steam, it reacts vigorously with steam to make magnesium oxide and hydrogen gas:

Mg (s) + H2O (g) → MgO (s) + H2 (g)

Reactions with chlorine

  • Group 2 metals react with chlorine gas to give the metal chloride 
    • For example

Mg (s) + Cl2 (g) → MgCl(s) 

Group 2 Oxides

Reactions of Group 2 oxides with water

  • All Group 2 oxides are basic, except for BeO which is amphoteric (it can act both as an acid and base)
  • Group 2 oxides react water to form alkaline solutions which get more alkaline going down the group

Group 2 Oxides reacting with Water

Group 2 oxide Reaction with water Observations
MgO MgO (s) + H2O (l) → Mg(OH)2 (s)  MgO is only slightly soluble in water, therefore a weakly alkaline solution (pH 10.0) is formed
CaO CaO (s) + H2O (l) → Ca(OH)2 (s)  A vigorous reaction which releases a lot of energy, causing some of the water to boil off as the solid lump seems to expand and open (pH 11.0)
SrO SrO (s) + H2O (l) → Sr(OH)2 (aq)   
BaO BaO (s) + H2O (l) → Ba(OH)2 (aq)   
  • Remember that:

oxide + water → hydroxide

  • You should know that calcium hydroxide, when in solution, is also called limewater

Reactions of Group 2 oxides with acid

  • Group 2 sulfates also form when a Group 2 oxide is reacted with sulfuric acid
  • The insoluble sulfates form at the surface of the oxide, which means that the solid oxide beneath it can’t react with the acid
  • This can be prevented to an extent by using the oxide in powder form and stirring, in which case neutralisation can take place
  • Remember that:

oxide + dilute hydrochloric acid → chloride + water

oxide + dilute sulfuric acid → sulfate + water

Reactions of Group 2 hydroxides

  • The Group 2 metal hydroxides form colourless solutions of metal salts when they react with a dilute acid
  • The sulfates decrease in solubility going down the group (barium sulfate is an insoluble white precipitate)

Group 2 Hydroxide Reactions with Dilute Acids

Group 2 hydroxide Reaction with dilute HCl Reaction with dilute H2SO4
Mg(OH)2 Mg(OH)2 (s) + 2HCl (aq) → MgCl2 (aq) + 2H2O (l) Mg(OH)2 (s) + H2SO4 (aq) → MgSO4 (aq) + 2H2O (l)
Ca(OH)2 Ca(OH)2 (s) + 2HCl (aq) → CaCl2 (aq) + 2H2O (l) Ca(OH)2 (s) + H2SO4 (aq) → CaSO4 (aq) + 2H2O (l)
Sr(OH)2 Sr(OH)2 (s) + 2HCl (aq) → SrCl2 (aq) + 2H2O (l) Sr(OH)2 (s) + H2SO4 (aq) → SrSO4 (s) + 2H2O (l)
Ba(OH)2 Ba(OH)2 (s) + 2HCl (aq) → BaCl2 (aq) + 2H2O (l) Ba(OH)2 (s) + H2SO4 (aq) → BaSO4 (s) + 2H2O (l)
  • Remember that:

hydroxide + dilute hydrochloric acid → chloride + water

hydroxide + dilute sulfuric acid → sulfate + water

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Philippa

Author: Philippa

Expertise: Chemistry

Philippa has worked as a GCSE and A level chemistry teacher and tutor for over thirteen years. She studied chemistry and sport science at Loughborough University graduating in 2007 having also completed her PGCE in science. Throughout her time as a teacher she was incharge of a boarding house for five years and coached many teams in a variety of sports. When not producing resources with the chemistry team, Philippa enjoys being active outside with her young family and is a very keen gardener.