sblock Elements - Result Question 1

####1. The temporary hardness of a water sample is due to compound X. Boiling this sample converts X to compound Y.X and Y, respectively, are

(2019 Main, 12 April II)

(a) Mg(HCO3)2 and Mg(OH)2

(b) Ca(HCO3)2 and Ca(OH)2

(c) Mg(HCO3)2 and MgCO3

(d) Ca(HCO3)2 and CaO

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Answer:

Correct Answer: 1. (d)

Solution:

  1. The temporary hardness of a water sample is due to compound X [i.e. Mg(HCO3)2 ]. Boiling of this sample converts X [i.e. Mg(HCO3)2] to compound Y[ i.e. Mg(OH)2]. Generally, temporary hardness is due to presence of magnesium and calcium hydrogen carbonates. It can be removed by boiling. During boiling, the soluble Mg(HCO3)2 is converted into insoluble Mg(OH)2 and Ca(HCO3)2 changed to insoluble CaCO3. These precipitates can be removed by filteration.

Mg(HCO3)2 Heating Mg(OH)2+2CO2

Ca(HCO3)2 Heating CaCO3+H2O+CO2



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