Reactions of Group 2
- The group 2 elements react with oxygen, water and dilute acids
Group 2 Reactions - Observations
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
- 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 of Group 2 metals with acid
- The Group 2 metals will react with dilute acids to form colourless solutions of metal salts
- For example, they will form colourless solutions of metal chlorides if reacted with hydrochloric acid
- When metals react with an acid, the by-product of this reaction is hydrogen gas
Group 2 Reactions with Dilute Acids - Equations
- When some of Group 2 metals react with sulfuric acid rather than hydrochloric, an insoluble sulfate forms
- Going down the group, the Group 2 sulfates become less and less soluble
- Calcium sulfate is sparingly soluble, but strontium sulfate and barium sulfate are insoluble
- The reaction of the metals with dilute HCl follows the following general equation:
M (s) + 2HCl (aq) → MCl2 (aq) + H2 (g)
- The reaction of the metals with dilute H2SO4 follows the following general equation:
M (s) + H2SO4 (aq) → MSO4 (aq) + H2 (g)
Remember that SrSO4 and BaSO4 are insoluble
Exam Tip
Learn the general equation for the reaction with water and for magnesium with steam. You could be asked or reactions of the oxides and hydroxides with acids.