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Learning Zone - The Chemical Reactivity Series

Back to Reactivity page Calcium, Ca back to reactivity page

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)

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