s-Block Elements : Calcium Hydroxide (Slaked lime)

Calcium Hydroxide (Slaked lime)

Preparation:

                   It is prepared by the action of water on quick time.

                             CaO + H2O → Ca(OH)2

Properties:

(1)     White amorphous solid.

(2)     It absorbs CO2 gas to form a white ppt of calcium carbonate which becomes colourless when excess of CO2 is passed.

                             Ca(OH)2 + CO2 → CaCO3 + H2

                             CaCO3 + H2O + CO2 → Ca (HCO3)2    

(3)     When heated with ammonium salt ammonia gas is obtained.

                             Ca(OH)2 + 2NH4Cl → CaCl2 + 2NH3 + 2H2O

(4)     Reactions of calcium hydroxide with chlorine give different products under different conditions. These are given as below:

                   (A)    Ca (OH)2 + Cl2 \underrightarrow { \quad Below\quad 3{ 5 }^{ 0 }C\quad } \quad   CaOCl2 + H2O

                   (B)    2Ca (OH)2 + 2Cl2 \quad \xrightarrow [ Red ]{ \quad Heat\quad }   2CaCl2 + 2H2 O+ O2 

                   (C)    2Ca (OH)2 + 2Cl2 → CaCl2 +  + 2H2O

                                      (cold and dil)                (Calcium chlorate)

                   (D)    6Ca (OH)2 + 6Cl2 → 5CaCl2 + Ca(ClO3)2 + 6H2O

                                      (hot and conc.)             (Bleaching powder)