Reactions of Group 2
- The group 2 elements react with oxygen, water and dilute acids
Group 2 Reactions - Observations
| Reaction with oxygen | Reaction with water | Reaction with dilute HCl | Reaction with dilute H2SO4 | |
| Mg | Burns easily Bright white light |
Vigorous reaction with steam, no reaction with water | Reacts vigorously | Reacts vigorously |
| Ca | Difficult to ignite Red flame |
Reacts moderately, forms a hydroxide | Reacts vigorously | Reaction slowed by the formation of a sparingly soluble sulfate layer on the metal, stopping hydrogen bubbles from rising |
| Sr | Difficult to ignite Red flame |
Reacts rapidly, forms a hydroxide | Reacts vigorously | Reaction is quickly stopped by the formation of an insoluble sulfate layer on the metal |
| Ba | Difficult to ignite Green flame |
Reacts rapidly, forms a hydroxide | Reacts vigorously | Reaction is quickly stopped by the formation of an insoluble sulfate layer on the metal |
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:
- Except for, Be which does not react with water
M (s) + 2H2O (l) → M(OH)2 (s) + H2 (g)
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 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
| Reaction with dilute HCl | Reaction with dilute H2SO4 | |
| Mg | Mg (s) + 2HCl (aq) → MgCl2 (aq) H2 (g) | Mg (s) + H2SO4 (aq) → MgSO4 (aq) + H2 (g) |
| Ca | Ca (s) + 2HCl (aq) → CaCl2 (aq) H2 (g) | Ca (s) + H2SO4 (aq) → CaSO4 (aq) + H2 (g) |
| Sr | Sr (s) + 2HCl (aq) → SrCl2 (aq) H2 (g) | Sr (s) + H2SO4 (aq) → SrSO4 (s) + H2 (g) |
| Ba | Ba (s) + 2HCl (aq) → BaCl2 (aq) H2 (g) | Ba (s) + H2SO4 (aq) → BaSO4 (s) + H2 (g) |
- 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
Examiner 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.
