Calcium word is derived from the Latin word ‘calx’, which means lime. It was discovered by British chemist Sir Humphry Davy in 1808 by the hydrolysis reaction, in which lime (CaO) and mercury oxide (HgO) were the reactants, and metallic calcium was isolated as the final product. It is classified as an alkaline earth metal. It is so-called because the oxides and hydroxides of calcium are alkaline in nature. It belongs to group 2 in the periodic table with atomic number 20.
Calcium is solid at room temperature, and as an alkaline earth metal, it possesses a silvery-white lustre and is a soft metal.
Although calcium is the fifth most abundant element in the earth’s crust, it is never found free in nature, and it is always found in a combined form, such as limestone (calcium carbonate), gypsum (calcium sulfate), fluorite (calcium fluoride), and apatite (calcium-phosphate mineral).
Calcium imparts characteristic brick red colour when placed in the flame. The detection of calcium element during qualitative analysis (academics related) is done through a flame test. Flame photometers are also available, which are used to estimate the concentration of calcium in the sample (during qualitative analysis).
Melting and Boiling Point
The melting point of calcium is 842°C, and its boiling point is 1484°C.
Reactivity towards Air
The main reason behind the existence of calcium in combined form is that it reacts instantly with air. It is readily attacked by air to form calcium oxides and calcium nitrides, and hence, it is never found free.
2Ca(s) + O2(g) → 2CaO(s) (calcium oxide)
3Ca(s) + N2(g) → Ca3N2(s) (calcium nitride)
Reactivity towards Water
It also reacts with water vigorously, even in cold water, to form calcium hydroxide with the liberation of hydrogen gas. The formation of bubbles inside the water shows the formation of hydrogen gas, and cloudy white precipitation shows the formation of calcium hydroxide.
Ca(s) + 2H2O(l) → Ca(OH)2(aq) +H2(g)
Reactivity towards Halogens
Calcium reacts with halogens (F, Cl, Br, I) upon heating and form dihalides.
Ca(s) + F2(g) → CaF2(s) (Calcium fluoride)
Calcium fluoride exists in nature as fluorite mineral.
Reactivity towards Acids
Calcium, being an alkaline earth metal, readily react with acids to liberate dihydrogen.
Ca + 2HCl → CaCl2 + H2
Calcium is an excellent reducing agent. It can be inferred from its large negative reduction potential value, i.e., -2.84V. Its reduction property is widely used in applications such as in the preparation of metals (chromium, thorium, uranium).
Calcium compounds are important compounds which have a wide range of applications in various industries. Calcium ions play a vital role in various biological processes occurring inside our bodies, and various calcium compounds are used in different calcium supplements.
1. Quicklime (Calcium Oxide)
Calcium oxide is a white amorphous solid, and it is usually produced in the form of hard humps. It emits bright limelight (usually white light) when heated in an oxyhydrogen flame. It has many applications such as in metallurgy, in the manufacturing of dyestuffs, and in drying gases and alcohol. Calcium oxide is widely used as a building material. It is an important constituent of portland cement (which is obtained by roasting limestone and sand with clay). Its large quantities are used in the steel industry, where it is used as a flux to remove P, S, and Si. It is also used as a lubricant in steel wire drawing and in neutralising wastes. Further, it is used in the chemical treatment of industrial water supplies; commonly used in water softening to remove the temporary hardness of the water. It is used in the manufacturing of glass and also used for the manufacture of insecticides and fungicides, such as Bordeaux mixtures( CuSO4/Ca(OH)2). It is also used in the dairy industry.
2. Calcium Hydroxide (Slaked lime)
The addition of a limited amount of water to lime (calcium hydroxide) breaks the lump of lime, and this process is called slaking of lime, and the product obtained is known as slaked lime. It appears as a white powder, and it is sparingly soluble in water. Its aqueous solution is called lime water. Paper and pulp industries consume large quantities of calcium hydroxide. During whitewashing, slaked lime is used, which combines with the atmospheric carbon dioxide to form calcium carbonate, which in turns gives the shiny texture to the walls. In the sugar manufacturing industry, slaked lime is used to remove impurities and colour from sugar solution during the sugar refining process.
3. Calcium Carbonate
Calcium carbonate is the main industrial chemical. Also, it is important for the production of quicklime and slaked lime. It has many applications in chemical, metallurgical, and construction industries. In the manufacturing of high-quality paper, calcium carbonate is extensively used. It has also pharmaceutical applications, such as an antacid, and as a source of calcium enrichment in diets. Various domestic applications of calcium are also known such as mild abrasives in toothpaste, and fillers in cosmetics.
4. Plaster of Paris (Calcium Sulphate)
Formula- CaSO4·½ H2O
Plaster of Paris is a hemihydrate of calcium sulphate. When gypsum (CaSO4. 2H20) is heated to 393K, Plaster of Paris is obtained.
2 (CaSO4 .2H2O) → 2 (CaSO4).H2O + 3H2O
Above this temperature, crystallization of water does not take place and we can obtain anhydrous calcium sulphate (CaSO4). This is also known as “dead burnt plaster.” It appears as a white powder and on mixing with water, it forms plastic mass which converts into a hard solid within 5 to 15 minutes and this process is called the “setting of Plaster of Paris”. This setting helps it to take shape of any mould in which it is added. This is the main property which is used for producing moulds for pottery and ceramics. Also, it is used for making statues, models and other decorative materials. In surgical bandages, it is used as a plaster for setting broken and fractured bones in the body.
Cement is a well-known construction material. It is considered as a necessary commodity in developing economies as it is used in concrete, in plastering, and in construction of building bridges and dams. Another name of cement is Portland cement because it shows resemblance with natural limestone that is extracted in the Isle of Portland, England. The key ingredients for the manufacture of cement are lime and clay, which fuse together first to give ‘cement clinker’ and then this clinker is mixed with gypsum, which finally gives us cement.
6. Medical Use
Biological role of Calcium in Human Body
Calcium Ca2+ ions play a significant role in the skeletal formation of the human body. In combination with phosphorous, it is the major constituent of bones, teeth, and shells. It has many biochemical roles in our body, for example, it acts as a messenger for hormonal action, act as a trigger for muscular contraction, plays a role in stabilization of protein structure, and helps in the maintenance of rhythm of the heart.
Food rich in Calcium
In our diet, dairy products, such as milk, cheese, and yoghurt are the rich sources of calcium. The other sources of calcium include green vegetables like broccoli, fruits such as orange and apricots, and canned fish with soft edible bones.
Calcium supplements are recommended by doctors during Osteoporosis (a disorder that weaken our bones) for its treatment and prevention. These supplements are also prescribed by the doctors when a patient suffers from certain digestive diseases, such as inflammatory bowel disease or celiac disease that decreases their ability to absorb calcium. These are also used for the prevention of certain types of cancer, such as calcium with vitamin D helps to protect premenopausal women (period of women’s life immediately after menopause) from breast cancer.
Types of Calcium Supplements
Calcium supplements contain different compounds of calcium and each compound of calcium contain varying amount of calcium mineral. Most commonly available calcium supplements are as follows:
Calcium Carbonate (contains 40% elemental calcium)
Calcium Citrate (contains 21% elemental calcium)
Calcium lactate (contains 13% elemental calcium)
Calcium gluconate (contains 9% elemental calcium)