Question

What happens when calcium reacts with water?

Answer 1

Hint: When the calcium metal sinks in water, after an hour or so bubbles are evident. We may implement this hint to construct our reaction and get to the products.

Complete step by step answer:

Properties of Calcium - Calcium is a silvery-white metal; it is relatively soft, but much harder than sodium metal. Calcium is a member of the alkaline-earth metals (Group II on the periodic table); these metals react vigorously with water, although not as violently as the Group I metals such as sodium or potassium.

Reaction of calcium metal with water - When calcium metal reacts with water, it reacts less violently. It produces a hydroxide known as calcium hydroxide (a cloudy white precipitate), and the bubbles of hydrogen gas produced are stuck to the surface of calcium. Due to which it floats over the water surface. Much less heat is produced in this reaction due to which hydrogen gas formed does not catch fire.

$Ca(s)\quad +\quad 2H_{ 2 }O(l)\quad \rightarrow \quad Ca(OH)_{ 2 }(aq)\quad +\quad H_{ 2 }\uparrow $

Stoichiometry of the reaction - 1 mole of calcium reacts with 2 moles of water to produce 1 mole of calcium hydroxide and 2 moles of hydrogen gas.

Hence, we can conclude that the reaction of calcium with water will form calcium hydroxide and hydrogen gas, where we can identify hydrogen gas by simply looking at the bubbles form and calcium hydroxide by the formation of cloudy white precipitate.

Note: The presence of the hydroxide is demonstrated by the addition of a few drops of phenolphthalein indicator, which turns the solution pink, indicating that the solution is basic.
Hydrogen gas is produced during the course of this reaction. If you are not collecting the gas, perform the procedure in a fume hood or a well-ventilated area to allow the gas to dissipate.