Some Important Compounds of Calcium: Calcium belongs to the \({\text{II}}\,{\text{A}}\) or \({2^{{\text{nd}}}}\) group of the periodic table and is one of the alkaline earth metals present in the \({\text{s}}\)-block. Calcium is the fifth most abundant element available on earth by weight. It occurs primarily in the form of \({\text{CaC}}{{\text{O}}_3},\) limestone, chalk, and marble. Some other minerals of Calcium, along with their chemical formula, are as follows:

1. Fluorspar or Fluorite: \({\text{Ca}}{{\text{F}}_2}\)
2. Gypsum: \({\text{CaS}}{{\text{O}}_4}.2{{\text{H}}_2}{\text{O}}\)
3. Anhydrite: \({\text{CaS}}{{\text{O}}_4}\)

Calcium Element

Calcium \(\left({{\text{Ca}}} \right)\) has:
Atomic number \( – 20\)
Atomic Mass \( – 40.08\)
Electronic Configuration \( – 1{{\text{s}}^2}2{{\text{s}}^2}2{{\text{p}}^6}3{{\text{s}}^2}3{{\text{p}}^6}4{{\text{s}}^2}\)

Calcium, being alkaline earth metal, can lose the last two electrons in the \({\text{4s}}\) orbital to form its compounds. Hence, it exhibits a \( + 2\) oxidation state in its compounds. Although both \( + 1\) and \( + 2\) oxidation states are probable, only \( + 2\) oxidation states are exhibited by \({\text{Ca}}\) due to the following reasons:

1. The divalent \(\left({ + 2} \right)\) state is more stable because it acquires the inert gas configuration after losing the last two electrons \(\left({{\text{Ar}}}\right).\)
2. The divalent cations form stronger lattices in the crystals due to their smaller size and higher charge in solid compounds of the element.
Calcium can be prepared in the laboratory by electrolysis in an aqueous solution containing \({\text{CaC}}{{\text{l}}_2}.\) Calcium metal gets deposited in the cathode.

Properties of Calcium

All alkaline earth metals are highly reactive since they have two extra electrons in the last s orbital, which they lose to get the noble gas configuration. Some important chemical properties are as follows:

A. Reaction with Water:
Calcium reaction with cold water rigorously and liberates hydrogen. It forms calcium hydroxide with water. Calcium has negative electrode potential, and therefore, the reactivity with water is extremely high.

\({\text{Ca + 2}}{{\text{H}}_2}{\text{O}} \to{\text{Ca}}{\left({{\text{OH}}} \right)_2} + {{\text{H}}_2}\)

B. With Air and Oxygen:
Calcium reacts readily with air and oxygen to form oxides and nitrides.

\({\text{2Ca + }}{{\text{O}}_2}\left({{\text{air}}} \right) \to 2{\text{CaO}}\)
\({\text{3Ca + }}{{\text{N}}_2}\left({{\text{air}}} \right) \to {\text{C}}{{\text{a}}_3}{{\text{N}}_2}\)

C. With Hydrogen:
Calcium reacts directly with hydrogen on heating to form calcium hydride.

\({\text{Ca + }}{{\text{H}}_2} \to {\text{Ca}}{{\text{H}}_2}\)

D. With Carbons:
When calcium or calcium oxide is heated with carbon in an electric furnace, it forms calcium carbide.

\({\text{Ca + 2C}} \to {\text{Ca}}{{\text{C}}_2}\left({1375\,{\text{K}}} \right)\)
\({\text{CaO + 3C}} \to {\text{Ca}}{{\text{C}}_2} + {\text{CO}}\left({2273\,{\text{K}}} \right)\)
\({\text{Ca}}{{\text{C}}_2}\) is a very important chemical intermediate, and when heated with atmospheric nitrogen at \(1375\,{\text{k}},\) it gives calcium cyanimide of formula \({\text{CaNCN}}\) or \({\text{CaC}}{{\text{N}}_2}.\)

E. Calcium imparts brick red colour to the flame.

List of Calcium Compounds and Formula

Some calcium compounds and their formula are as follows:

Calcium Compounds	Formula
Calcium Oxide or Quick Lime	\({\text{CaO}}\)
Calcium Hydroxide Or slaked lime	\({\text{Ca}}{\left({{\text{OH}}} \right)_2}\)
Calcium Carbonate	\({\text{CaC}}{{\text{O}}_3}\)
Calcium sulphate Hemihydrate or plaster of. paris	\({\text{CaS}}{{\text{O}}_4}.1/2{{\text{H}}_2}{\text{O}}\)

Cement is also a very industrially significant mixture of calcium silicates and aluminates with some quantities of gypsum. Important compounds, their preparation, properties, and uses are discussed below.

Compounds of Calcium and Their Uses

1. Calcium Oxide or Quick Lime (CaO)

Preparation:

Calcium oxide or quick lime is prepared on a large scale from limestone by heating it in a rotary kiln at a temperature of about \(1070\) to \(1270\,{\text{k}}.\left({\Delta {\text{H}} = + 179.9\,{\text{kJ}}} \right)\)
\({\text{CaC}}{{\text{O}}_3} \leftrightarrow {\text{CaO}} + {\text{C}}{{\text{O}}_2}\left({1070 – 1270\,{\text{k}}} \right)\)

It is a reversible reaction. Hence, Carbon dioxide is removed as and when it is formed in order for the reaction to proceed in the forward reaction to give quick lime and for the reaction to complete.

Another aspect that needs to be controlled is the temperature. The temperature is kept within \({1270\,{\text{k}}}\) since, beyond that, the silica present as an impurity in limestone reacts with the Calcium oxide formed to give calcium silicate.
\({\text{CaO}} + {\text{Si}}{{\text{O}}_2} \to {\text{CaSi}}{{\text{O}}_3}\left({{\text{above }}1270\,{\text{k}}} \right)\)

Properties of Calcium Oxide:

a. Calcium oxide is an amorphous powder and has a melting point of \({{\text{28}}70\,{\text{k}}}.\)
b. When calcium oxide is heated in an oxyhydrogen flame, it gives out bright white light, which is called the limelight.
c. Calcium oxide, when prepared, is obtained in the form of hard clumps. A little amount of water is added to the lumps to break them into powder. At the addition of water, it reacts with water with a large hissing sound, and heat is evolved in the reaction, thereby converting water into steam. This process is called slaking of lime, and the powder obtained from the process is called slaked lime.\(\Delta {\text{H}} = \, – 64.5\,{\text{kJ}}/{\text{mol}}\)
\({\text{CaO}} + {{\text{H}}_2}{\text{O}} \to {\text{Ca}}{\left({{\text{OH}}} \right)_2}\)
d. Calcium oxide, when exposed to air, absorbs moisture and carbon dioxide from it, thereby forming slaked lime and calcium carbonate, respectively.
\({\text{CaO}} + {{\text{H}}_2}{\text{O}} \to {\text{Ca}}{\left({{\text{OH}}} \right)_2}\)
\({\text{CaO}} + {\text{C}}{{\text{O}}_2} \to {\text{CaC}}{{\text{O}}_3}\)
e. Calcium Oxide on slaking with caustic soda gives a solid compound called Soda-lime \(\left({{\text{CaO}} + {\text{NaOH}}} \right).\)

Uses of Calcium Oxide:

a. Calcium oxide is a primary material in many manufacturing industries.
b. It is used as a constituent in mortar, and therefore, used in building constructions.
c. Used for drying alcohols and non-acidic gases and in preparation of ammonia and soda-lime \(\left({{\text{CaO}} + {\text{NaOH}}} \right).\)

2. Calcium Hydroxide [Slaked Lime,Ca(OH)₂]

Calcium hydroxide can be prepared from quick lime and calcium chloride.

a. Preparation from quick lime: Water is added to quick lime to prepare calcium hydroxide on a commercial scale. The process is called as slaking of lime. In the process of slaking, the lumps of quicklime crumble to a fine powder.
\({\text{CaO + }}{{\text{H}}_2}{\text{O}} \to {\text{Ca}}{\left({{\text{OH}}} \right)_2}\)
b. Calcium chloride reacts with caustic soda to give calcium hydroxide.
\({\text{CaC}}{{\text{l}}_2}{\text{ + 2NaOH}} \to {\text{Ca}}{\left({{\text{OH}}}\right)_2} + 2{\text{NaCl}}\)

Properties of Calcium Hydroxide:

a. Calcium hydroxide is a white, amorphous powder and is sparingly soluble in water. With the rise in temperature, the solubility of calcium hydroxide decreases.
b. Milk of Lime: A suspension of calcium hydroxide (slaked lime) in water is called as milk of lime. This, when filtered, a clear solution is obtained and is known as lime water.
c. With heat: Calcium hydroxide, when heated above \(700\,{\text{k}},\) loses water to give calcium oxide.
\({\text{Ca}}{\left({{\text{OH}}} \right)_2}{\text{ + CaO}} + {{\text{H}}_2}{\text{O}}\left({{\text{Heat}} > 700{\text{K}}} \right)\)
d. With Chlorine: Calcium hydroxide, on reaction with chlorine, forms calcium hypochlorite, a component of bleaching powder.
\({\text{2Ca}}{\left({{\text{OH}}}\right)_2} + 2{\text{C}}{{\text{l}}_2} \to {\text{CaC}}{{\text{l}}_2} + {\text{Ca}}{\left({{\text{OCl}}} \right)_2} + 2{{\text{H}}_2}{\text{O}}\)
e. Calcium hydroxide, along with sodium carbonate, finds its use in softening the temporary hardness in water.

Uses:

a. Calcium hydroxide, in the form of mortar, is helpful as a building material. The mortar is prepared by mixing slaked lime with \(3 – 4\) times its weight of sand. This mixture thus prepared is mixed slowly with water to form a paste, called mortar.
b. Slaked lime has disinfectant properties, and therefore, is used for whitewashing.
c. Slaked lime is used in the manufacture of bleaching powder, in the purification of sugar, the tanning industry, and also in glass making.

3. Calcium Carbonate CaCO₃

Calcium carbonate or limestone occurs in nature in the form of chalk, corals, marble, calcite, etc. When it is mixed with magnesium carbonate, it is present in nature in the form of dolomite.

Preparation:

a. Preparation using slaked lime: When a measured quantity of carbon dioxide is passed over slaked lime, calcium carbonate is formed.
\({\text{Ca}}{\left({{\text{OH}}} \right)_2}{\text{ + C}}{{\text{O}}_2} \to {\text{CaC}}{{\text{O}}_3} + {{\text{H}}_2}{\text{O}}\)
b. Preparation from calcium chloride: The addition of an aqueous solution of sodium carbonate to calcium chloride gives calcium carbonate.
\({\text{CaC}}{{\text{l}}_2} + {\text{N}}{{\text{a}}_2}{\text{C}}{{\text{O}}_3} \to {\text{CaC}}{{\text{O}}_3} \downarrow + 2{\text{NaCl}}\)

Properties:

a. Calcium carbonate is a white solid and is insoluble in water.
b. When heated to about \(1070 – 1270\,{\text{k}},\) calcium carbonate decomposes to release carbon dioxide, and Calcium oxide is formed.
c. Calcium carbonate in action with dilute acids liberating carbon dioxide.
\({\text{CaC}}{{\text{O}}_3}{\text{ + 2HCl}} \to {\text{CaC}}{{\text{l}}_2}{\text{ + C}}{{\text{O}}_2} + {{\text{H}}_2}{\text{O}}\)

Uses:

a. Calcium carbonate is used as a flux in metal extraction, along with magnesium carbonate.
b. The specially precipitated calcium carbonate is used in the manufacture of high-quality paper.
c. They are used as a raw material in the manufacturing of sodium carbonate through the Solvay-ammonia process

4. Calcium Sulphate Hemihydrate or Plaster of Paris

Calcium Sulphate hemihydrate or plaster of Paris has a formula of \({\text{CaS}}{{\text{O}}_4}.1/2{{\text{H}}_2}{\text{O}}.\)

Preparation:

Calcium sulphate hemihydrate is prepared by heating gypsum at \(393\,{\text{k}}.\) Care must be taken to not allow the temperature to rise above \(393\,{\text{k}},\) as after this temperature limit, all water of crystallization will be lost, therefore resulting in anhydrous calcium sulphate, which is also called as dead burnt plaster.
\({\text{2CaS}}{{\text{O}}_4}{\text{.2}}{{\text{H}}_2}{\text{O}} \to 2{\text{CaS}}{{\text{O}}_4}.1/2{{\text{H}}_2}{\text{O + 3}}{{\text{H}}_2}{\text{O}}\left({393\,{\text{k}}} \right)\)

Properties:

a. Plaster of Paris is a white powder and comes with a remarkable settling property with water. When mixed with water (\(1/3\) its weight), it forms a hard, interlocking mass of crystals within \(5\) to \(15\) minutes. This plaster formed is set even faster with the addition of common salt. The setting takes place because of the rehydration of plaster of Paris and its conversion to gypsum. The rehydration process enhances the volume by \(1\% ,\) resulting in giving the plaster the shape of the mold on which it is set.
\({\text{2CaS}}{{\text{O}}_4}.1/2{{\text{H}}_2}{\text{O + 3}}{{\text{H}}_2}{\text{O}} \to {\text{2CaS}}{{\text{O}}_4}.2{{\text{H}}_2}{\text{O}}\)

Uses:

1. Plaster of Paris is used extensively to make pottery, ceramics, statues, busts, and many more items. It is also used in the construction industry.
2. Plaster of Paris finds its use in medicine to produce surgical bandages.
3. It is also used in dentistry for various applications involving molds.

Summary

Calcium belongs to the Alkaline Earth metals and the ‘s’ block of the periodic table. Owing to the two s electrons in its ultimate shell, it prefers \( + 2\) oxidation state, which is its stable oxidation state. Calcium forms several industrially important compounds, such as Plaster of Paris, slaked lime, Quick lime, and calcium carbonate. It is also used in dentistry for various applications involving molds.

Learn About Calcium Chloride Formula

Frequently Asked Questions

Q.1. What are the examples of a few calcium compounds?
Ans: Some examples of calcium compounds include calcium carbonate, calcium sulphate, calcium oxide, calcium nitride and calcium hydroxide.

Q.2. What is the most common calcium compound?
Ans: Common calcium compounds include calcium carbonate, calcium sulphate hemihydrate or plaster of Paris, quick lime or calcium oxide, and Slaked lime or calcium hydroxide.

Q.3. What are the uses of Calcium or what is calcium used for?
Ans: Calcium, in the form of its compounds, is used for many purposes, including industrial purpose as plaster of Paris, bleaching powder, and building materials, in cement industry and many more.

Q.4. What is the chemical composition of Plaster of Paris?
Ans: Plaster of Paris is calcium sulphate hemihydrate. It has a chemical composition of \({\text{CaS}}{{\text{O}}_4}.1/2{{\text{H}}_2}{\text{O}}.\)

Q.5. What is the chemical formula for quick lime?
Ans: Quick lime is calcium oxide, and it has a formula of \({\text{CaO}}{\text{.}}\)

We hope this detailed article on some important compounds of calcium helped you in your studies. If you have any doubts, queries or suggestions regarding this article, feel to ask us in the comment section and we will be more than happy to assist you. Happy learning!