11.2 Reactions of Group II Elements
Reaction with oxygen gas, O2
- All Group II elements(except beryllium) burn in oxygen with a bright flame to form monoxides
2M(s) + O2(g) → 2MO(s) ; where M = A Group II element
-
- 2Mg(s) + O2(g) → 2MgO(s) ; burns with brilliant white flame
- 2Ca(s) + O2(g) → 2CaO(s) ; burns with brick red flame
- 2Sr(s) + O2(g) → 2SrO(s) ; burns with crimson red flame
- 2Ba(s) + O2(g) → 2BaO(s) ; burns with apple green flame
Reaction with water, H2O
- All Group II elements(except beryllium) reacts with water to form hydroxides and hydrogen gas
M(s) + 2H2O(l) → M(OH)2(aq) + H2(g) ; where M = A Group II element
- Beryllium has no reaction with cold water or steam even at red heat due to the formation of protective oxide layer on its surface.
- Magnesium reacts very slowly with cold water, taking several days to collect a test tube of hydrogen gas and a weakly alkaline magnesium hydroxide solution.
Mg(s) + 2H2O(l) → Mg(OH)2(aq) + H2(g) ; very slow, pH = 9 However, it reacts rapidly with steam to produce magnesium oxide and hydrogen gas. This is because the hydroxide formed thermally decompose into an oxide.
Mg(s) + H2O(g) → MgO(s) + H2(g) ; very fast
- Calcium, strontium and barium reacts vigorously with cold water to give hydroxides
Ca(s) + 2H2O(l) → Ca(OH)2(s) + H2(g)
Sr(s) + 2H2O(l) → Sr(OH)2(aq) + H2(g)
Ba(s) + 2H2O(l) → Ba(OH)2(aq) + H2(g)
Note:
- Ca(OH)2 appears as white It is sparingly soluble therefore a weakly alkaline solution will also be formed.
- The reactivity of the elements with water increases down the In other words, they become more soluble going down the Group.
Reaction with acids
- All Group II elements react with acid to give hydrogen gas and the corresponding salt
M(s) + H⁺(aq) → M²⁺(aq or s) + H2(g) ; where M = A Group II element
- Beryllium reacts slowly with acids and has no reaction at room temperature.
- The rest of Group II metals react with increasing vigorous going down the Group