s-Block Elements : CALCIUM (Ca)

CALCIUM (Ca)

Source

                   Chlorapatite                –       Ca5(PO4)3Cl

                   Phosphorite                 –      Ca3(PO4)2

                   Fluorapatite                –       Ca5(PO4)3F

                   Fluorspar                     –      CaF2

                   Anhydrite                    –       CaSO4

                   Gypsum                       –      CaSO4.2H2O

                   Dolomite                     –      MgCO3.CaCO3

 

Extraction of Ca :

(1)     By electrolysis of fused mixture of CaF2 and CaCl2 at 650ºC

                             CaCl2 → Ca+2 + 2Cl 

                             Electrolyte          –       CaF2 + CaCl2

                             Anode                 –       Graphite

                             Cathode              –       Iron rod.

                   Reaction

                             Cathode → Ca+2 + 2e → Ca

                             Anode → 2Cl – 2e → Cl2

                    (2)     By reduction of CaCl2 with Al

                             3CaCl2 + 2A1 → 2AlCl3 + 3Ca

                    (3)     By Gold Schmidt (Thermite) process

                             3CaO + 2Al → Al2O3 + 3Ca.

 

Properties of Ca :

(1)     Greyish white crystalline metal with silvery lustre.

(2)     Calcium reacts with oxygen to form calcium oxide

                                                2Ca + O2 → 2CaO

(3)     With hydrogen it reacts to form calcium hydride.

                                                Ca + H2 → CaH2 

(4)     It readily reacts with chlorine to form calcium chloride

                                                Ca + Cl2 → CaCl2

(5)     On heating with nitrogen, calcium forms calcium nitride.

                                                3Ca + N2 \underrightarrow { \quad \Delta \quad } Ca3N2

(6)     Due to its high oxidation potential it displaces H2 from H2­O and dil acids

                   (A)    Ca + 2H2O → Ca(OH)2 + H2         

                   (B)    Ca + 2HCl → CaCl2 + H2

(7)     It reacts with carbondioxide on heating to form calcium oxide and calcium carbide.

                             5Ca + 2CO2 \underrightarrow { \quad \Delta \quad } 4CaO + CaC2

(8)     It reduces Cr2O3 to chromium.

                             Cr2O3 + 3Ca → 3CaO + 2Cr

(9)     It reacts with ammonia water at different temperatures to form different products.

                             Ca + 6NH3 → Ca (NH3)6

                             Ca (NH3)6  \underrightarrow { \quad \Delta \quad } Ca(NH2)2 + 4NH3 + H2

                             3Ca (NH2)2 \underrightarrow { \quad \Delta \quad } Ca3N2 + 4NH3