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The S-Block Elements

Question
CBSEENCH11007159
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Describe briefly the preparation and uses of magnesium chloride (MgCl2.6H2O).

Solution

Preparation:
(i) In the laboratory, magnesium chloride is prepared by the action of hydrochloric acid on magnesium oxide or carbonate. 
         MgO space plus space 2 HCl space rightwards arrow space space MgCl subscript 2 space plus space straight H subscript 2 straight O MgCO subscript 3 space plus space 2 HCl space rightwards arrow space space MgCl subscript 2 space plus space CO subscript 2 space plus space straight H subscript 2 straight O
The reaction mixture is cooled and concentrated when crystals of MgCl2.6H2O separate out.
(ii) From carnallite: The mineral carnallite (KCl.MgCl2.6H2O) is powdered and then boiled with water. On cooling KCl is crystallised out while magnesium chloride is left in the mother liquor. The mother liquor is separated, concentrated by evaporation and cooled when crystals of MgCl2.6H2O separate out.
(iii) From sea water: Sea water is concentrated and then treated with lime when magnesium hydroxide gets precipitated. 
      stack MgCl subscript 2 with Sea space water below space plus space Ca left parenthesis OH right parenthesis subscript 2 space space rightwards arrow space space space stack Mg left parenthesis OH right parenthesis subscript 2 with ppt. below space plus space CaCl subscript 2
The precipitate of Mg(OH)2 is dissolved in HCl when a solution of magnesium chloride is obtained. The solution of magnesium chloride on concentration and cooling yields crystals of MgCl2.6H2O.
Mg left parenthesis OH right parenthesis subscript 2 space plus space 2 HCl space rightwards arrow space space MgCl subscript 2 space plus space 2 straight H subscript 2 straight O
 It is used:
(i) in the preparation of magnesia cement.
(ii) in the extraction of magnesium metal. 

Some More Questions From The s-Block Elements Chapter

Which is the most reactive alkali metal and why?

Why alkali metals do not form M2+ ions?

Name the radio active element in group 1. How does it resemble with the remaining elements of the group?

Why alkali metals are normally kept in kerosene oil?

Why lithium cannot be stored in kerosene?

Why does lithium form complexes?

Why are alkali metal ions diamagnetic and colourless?

Why are alkali metals the most electropositive in nature?

Explain why is sodium less reactive than potassium.

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