11.2Reactions of Group II Elements

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.
  1. 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:

  1. 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