Question

Carnallite is a reddish or white mineral and represented by the formula ${\text{KMgC}}{{\text{l}}_{\text{3}}} \cdot {\text{6}}{{\text{H}}_{\text{2}}}{\text{O}}$ .
(A). True
(B). False

Answer 1

Hint : Carnallite is a chloride mineral which is mined for both potassium and magnesium. It is variably coloured and sometimes colourless also. Carnallite is an evaporite mineral. It is formed by concentration and crystallisation by evaporation from an aqueous solution. Evaporite minerals are water soluble sediments and classified under sedimentary rocks.

Complete Step By Step Answer:
Carnallite is a double chloride mineral of potassium and magnesium. It forms under specific environmental conditions in an evaporating sea or sedimentary basin.
We know that halides are composed of halogen and a metal ion. In this case, the given mineral carnallite is composed of potassium chloride and magnesium chloride with crystallisation of water.
Potassium can form ionic bonds with one atom of chlorine and thus, the formula of potassium chloride is: ${\text{KCl}}$ .
Magnesium can form ionic bonds with two atoms of chlorine and thus, the formula of magnesium chloride is: ${\text{MgC}}{{\text{l}}_2}$ .
Now, carnallite has six molecules of crystallisation of water in one mole of it.
Therefore, its chemical formula is ${\text{KCl}} \cdot {\text{MgC}}{{\text{l}}_2} \cdot {\text{6}}{{\text{H}}_{\text{2}}}{\text{O}}$ . This formula can be simplified and written as: ${\text{KMgC}}{{\text{l}}_{\text{3}}} \cdot {\text{6}}{{\text{H}}_{\text{2}}}{\text{O}}$ .
This mineral is deliquescent and found in many colours ranging from colourless, white to yellow, reddish and blue.
Hence, the given statement is true and the correct option is (A).

Note :
Carnallite is not to be confused with ‘Kainite’ which is a sulphate mineral of potassium and magnesium. Its chemical formula is ${\text{KCl}} \cdot {\text{MgS}}{{\text{O}}_4} \cdot {\text{3}}{{\text{H}}_{\text{2}}}{\text{O}}$ .