Get premium membership and access revision papers with marking schemes, video lessons and live classes.

Processing. Please wait.

Reaction of alkaline earth metals with cold water.

Answer Text:
2. Reaction of alkaline earth metals with cold water.
- Alkaline earth metals react slowly with cold water to form corresponding hydroxides and hydrogen gas.
Examples
Magnesium:
- Reacts slowly with water to form magnesium hydroxide and hydrogen gas.
- The reaction is very slow and the amount of hydrogen gas evolved is very low hence the
hydrogen gas bubbles stick on the surface of the metal.
- The magnesium hydroxide formed dissolves slightly in water to form magnesium hydroxide.
- Thus the resultant solution is slightly alkaline.
Equation:
#Mg(s) + 2H_2O(l) → Mg(OH)_2(aq) + H_2(g).#
Calcium:

Observations and explanations:
- Calcium sinks to the bottom of the beaker; because it is denser than water;
- Slow effervescence of a colourless gas; due to slow evolution of hydrogen gas;
- Soapy solution formed; due to formation of alkaline calcium hydroxide;
- A white suspension is formed; because calcium hydroxide is slightly soluble in water;
Reaction equation:
#Ca(s) + H_2O (l) → Ca (OH)_2(aq) + H_2 (g)#;
Effect of resultant solution on litmus paper;
- Litmus paper slowly turns blue; calcium hydroxide formed is slightly soluble in water;
releasing a small number of hydroxyl ions which result into alkaline conditions // high pH;