Question

State the visible change and give equations for the action when a piece of $Ca$ is added to cold water.

Answer 1

Calcium is a member of the group $II$ in the periodic table and belongs to alkaline earth metals. Elements belonging to the group $II$ react vigorously with water but not as vigorously as group $I$ elements like sodium and potassium. Calcium is a silvery-white metal in appearance and is comparatively harder in comparison to sodium and potassium. Its symbol is $Ca$ and the atomic number is 20. It also reacts with air to form an oxide layer on it and its chemical properties are similar to its heavier homologs strontium and barium which belong to the same group.

Complete step by step answer:
When a piece of calcium metal is added to a beaker containing water then calcium metal will start to bubble vigorously as it will start reacting with water and evolve hydrogen gas.
A cloudy white precipitate of calcium hydroxide is also formed along with hydrogen gas.
After some time, the piece of calcium metal will sink in water and bubbles can still be seen on the surface of the metal piece.
The reaction of calcium metal with water is exothermic as it releases heat on reaction with water.
The balanced chemical equation for the above reaction is:
$Ca(s) + 2{H_2}O(l) \to Ca{(OH)_2}(aq) + {H_2}(g)$
(Hydrogen gas is evolved along with calcium hydroxide as a precipitate)

Note:
The solution we get after the reaction is basic due to the presence of calcium hydroxide.
Since hydrogen gas is produced in the reaction it must be collected or the reaction should be performed in a fume hood or a well-ventilated area.
The reaction of calcium with water is less violent in comparison to sodium and potassium.
Group $II$ metals become more reactive towards the water as we go down the group