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:

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JEE Mains Previous Paper 1 (Held On: 12 Apr 2019 Shift 2)
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  1. Mg(HCO3)2 and Mg(OH)2
  2. Ca(HCO3)2 and Ca(OH)2
  3. Mg(HCO3)2 and MgCO3
  4. Ca(HCO3)2 and CaO

Answer (Detailed Solution Below)

Option 1 : Mg(HCO3)2 and Mg(OH)2
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JEE Main 04 April 2024 Shift 1
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90 Questions 300 Marks 180 Mins

Detailed Solution

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Concept:

The temporary hardness is caused by bicarbonates of calcium and magnesium. On boiling following changes occurs,

On boiling, the bicarbonates salt of magnesium Mg(HCO3)2, the solution produces the magnesium hydroxide to decompose and yielding carbon dioxide and hydrogen.

\({\rm{Mg}}{\left( {{\rm{HC}}{{\rm{O}}_3}} \right)_2}\left( {{\rm{aq}}} \right)\mathop \to \limits^{{\rm{\;boiling\;}}} {\rm{Mg}}{({\rm{OH}})_2} + {\rm{C}}{{\rm{O}}_2} \uparrow + {{\rm{H}}_2} \downarrow \)

Calcium hydrogen carbonate on boiling will produce calcium carbonate with carbon dioxide and hydrogen.

\({\rm{Ca}}{\left( {{\rm{HC}}{{\rm{O}}_3}} \right)_2}\left( {{\rm{aq}}} \right)\mathop \to \limits^{{\rm{\;boiling\;}}} {\rm{CaC}}{{\rm{O}}_3}{\rm{\;}} + {\rm{C}}{{\rm{O}}_2} \uparrow + {{\rm{H}}_2} \downarrow \)

X = Mg(HCO3)2

Y = Mg(OH)2
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