Reaction with water
When a small piece of calcium is added to water, it sinks to the bottom of the water. Colorless gas bubbles evolved at a moderate
rate. Unlike potassium or sodium, this experiment is safe enough to capture the gas produces, which gives a pop sound with a burning splint, indicative
of hydrogen gas.
A milky suspension is produced, as the white calcium hydroxide
formed is only slightly soluble in water. However, the alkaline solution produced is still strong enough to turn red litmus to blue.
Calcium + water > calcium hydroxide + hydrogen
Ca(s) + 2H2O(l) > Ca(OH)2(aq) + H2(g)
Reaction with oxygen
Calcium burns quite vigorously in oxygen and strong heating is
required to make it burn. It gives a brick red flame to produce
a white powder of calcium oxide.
Calcium + oxygen > calcium oxide
2Ca(s) + O2(g) > 2CaO(s)
Reaction with dilute acids
The following experiment should be carried out with care.
Calcium reacts with dilute hydrochloric acid to give calcium chloride and hydrogen gas.
calcium + dilute hydrochloric acid > calcium chloride + hydrogen
Ca(s) + 2HCl(aq) > CaCl2(aq) + H2(g)
Calcium reacts with dilute sulphuric acid to give calcium sulfate and hydrogen gas.
Initial reaction is fast, but gradually slows down. This is because calcium sulfate is quite insoluble in water, which forms a protective layer on
calcium and preventing the acid to react effectively with calcium.
Calcium + dilute sulphuric acid > calcium sulphate + hydrogen
Ca(s) + H2SO4(aq) > CaSO4(s) + H2(g)
Calcium reacts with dilute nitric acid to give calcium nitrate and hydrogen gas.
calcium + dilute nitric acid > calcium nitrate + hydrogen
Ca(s) + 2HNO3(aq) > Ca(NO3)2(aq) + H2(g)