9. Some important compounds of calcium

SOME IMPORTANT COMPOUNDS OF CALCIUM

(i) Calcium Oxide or Quick Lime, CaO

Uses:
(i) In the manufacture of cement, sodium carbonate, calcium carbide etc.
(ii) Used in the purification of sugar.
(iii) In the manufacture of dye stuffs.

(ii) Calcium Hydroxide (Slaked lime), Ca(OH)₂

Carbonates
Carbonates of alkaline earth metals are thermally unstable and decompose on heating.

Calcium hydroxide is prepared by adding water to quick lime, CaO. It is a white amorphous powder. It is sparingly soluble in water. The aqueous solution is known as lime water and a

suspension of slaked lime in water is known as milk of lime. When carbon dioxide is passed through lime water it turns milky due to the formation of calcium carbonate.

Uses:
(i) It is used in the manufacturing of building material.
(ii) Used in white-wash as a disinfectant.
(iii) Used to detect C0₂ gas in the laboratory.

(iii) Calcium Carbonate or Limestone (CaC0₃)
Preparation: Calcium carbonate occurs in nature in different forms like limestone, marble, chalk etc. It can be prepared by passing C0₂ through slaked lime in limited amount.
Ca(OH)₂ + C0₂  ——>  CaC0₃ + H₂0

It can also prepared by the reaction of a solution of sodium carbonate with calcium chloride.
CaCl₂ + Na₂C0₃  ——>  CaC0₃ + 2NaCl
Uses:
(i) In the manufacturing of Quick Lime.
(ii) With MgC0₃ used as flux in the extraction of metals.
(iii) Used as an antacid.
(iv) In the manufacture of high quality paper.

(iv) Calcium Sulphate (Plaster of Paris) CaS0₄-1/2H₂0
Preparation: It is obtained when gypsum CaS0₄– 2 H₂0 is heated to 393 K
2(CaS0₄-2H₂0) ———-> 2(CaS04) . H₂0 + 3H₂0
Above 393 K anhydrous CaS04 is formed, which is called ‘dead burnt plaster’.
Properties:
(i) It is a white atmosphous powder.
(ii) When it is mixed in adequate quantity of water it forms a plastic hard mass within 15 minutes.
Uses:
(i) Commonly used in making pottery, ceramics etc.
(ii) Used in the surgical bandages for setting the fractured bone or sprain.
(iii) For making statues, ornamental work, decorative material etc.

(v) Cement
Preparation: Prepared by combining a material rich in CaO with other material such as clay, which contains Si0₂ along with the oxides of aluminium, iron and magnesium.

Important Ingredients of portland cement:
(Ca₂Si0₄) dicalcium silicate 26%
(Ca₂SiO₄) Tricalcium silicate 51%
(Ca₃Al₂0₆) Tricalcium Aluminate 11%
Uses:
In plastering and in construction purposes.
• s-block elements constitute Group I and II elements.
• General electronic configuration of
Group I = [Noble gas] ns¹
Group II = [Noble gas] ns²
• Diagonal Relationship

The first three elements of second period (Li, Be, B) show diagonal similarity with the elements (Mg, Al, Si) of third period. Such similarities are termed as diagonal relationship.
• The alkali metals are silvery-white soft metals. They are highly reactive. Their aqueous solutions are strongly alkaline in nature. Their atomic and ionic sizes increase on moving down the group and ionization enthalpies decrease systematically down the group.
• Alkaline earth metals. They are much similar to alkali metals but due to small size some differences are there. Their oxides and hydroxides are less basic than the alkali metals.
• Sodium hydroxide (NaOH) is prepared by the electrolysis of aq NaCl in Castner- Kellner cell.
Slaked lime Ca(OH)₂ is formed by the action of quick lime on water.
• Gypsum is CaS0₄. 2 H₂0. On heating upto 390 K CaS0₄/2H₂0 (plaster of paris) is formed.