The compound A on heating gives a colourless gas and a residue that is dissolved in water to obtain B. Excess of CO2 residue that is dissolved in water to obtain B. Excess of is recovered in the solid form. Solid C on gentle heating gives back A. The compound is

A
${CaSO}_{4} \cdot 2 H_{2} O$
B
${CaCO}_{3}$
C
${Na}_{2} {CO}_{3}$
D
$K_{2} {CO}_{3}$

Solution:

$\begin{array}{ccc} {CaCO}_{3 (s)} & \overset{Δ}{⟶} {CO}_{2 (g)} ↑ & + {CaO}_{(s)} \\ A & colourless & B \end{array} \underset{B}{{CaO}_{(s)}} + H_{2} O ⟶ Ca (OH)_{2 (aq)} Ca (OH)_{2} + 2 {CO}_{2} ⟶ Ca {({HCO}_{3})}_{2 (aq)} Ca {({HCO}_{3})}_{2 (s)} ⟶ \underset{A}{⟶} {CaCO}_{3 (s)} + {CO}_{2 (g)} + H_{2} O_{(g)} ∴ Correct choice : (b)$

The compound A on heating gives a colourless gas and a residue that is dissolved in water to obtain B. Excess of CO₂ residue that is dissolved in water to obtain B. Excess of is recovered in the solid form. Solid C on gentle heating gives back A. The compound is

Solution:

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