Question

a compound x on heating gives a colourless gas . the residus is dissolve in water to obtain y , excess CO2 is bubbled through aqueous solution of y and z is formed. z on gentle heating gives back x the x is ?

Answer 1

Please check attached image

Answer 2

Answer :

$X=CaCO_3(\text{Calcium carbonate})\\Y=Ca(OH)_2(\text{Calcium hydroxide})\\Z=Ca(HCO_3)_2(\text{Calcium bicarbonate})$

Explanation :

When a compound X, (calcium carbonate) on heating gives a colorless gas (carbon dioxide) and residue (calcium oxide) as a product then residue is dissolved in water to obtain Y (calcium hydroxide) and then excess carbon dioxide is bubbled through aqueous solution of Y (calcium hydroxide) it forms Z (calcium bicarbonate). On gentle heating, Z (calcium bicarbonate) gives back X (calcium carbonate).

When the excess carbon dioxide gas is passed through the calcium hydroxide, it turns milky first due to the formation of the calcium carbonate as a precipitate which is insoluble in water and then become colorless due to the formation of calcium bicarbonate. On passing excess of carbon dioxide gas, the colorless calcium bicarbonate is formed.

The balanced reactions will be,

$CaCO_3\overset{\Delta}\rightarrow CaO+CO_2\\\\CaO+H_2O\rightarrow Ca(OH)_2\\\\Ca(OH)_2+CO_2\rightarrow Ca(HCO_3)_2\\\\Ca(HCO_3)_2\overset{\Delta}\rightarrow CaCO_3+H_2O+CO_2$