Discussion Forum



1)

 A compound X  on heating gives a colourless gas. The residue is dissolved in water to obtain Y. Excess CO2 is passed through aqueous solution of Y when Z  is formed. Z on gentle heating gives back X  . The compound X is 


A) $Ca(HCO_{3})_{2}$

B) $CaCO_{3}$

C) $NaHCO_{3}$

D) $Na_{2}CO_{3}$

Answer:

Option B

Explanation:

$CaCO_{3}$  $\underrightarrow{\triangle}$ $CaO+CO_{2}\uparrow$

   X                                   colourless gas

 $ CaO+H_{2}O\rightarrow Ca(OH)_{2}$

  Residue                        Y

$ Ca(OH)_{2}+2CO_{2}\rightarrow  Ca(HCO_{3})_{2}$

   Y             excess                      Z

$ Ca(HCO_{3})_{2}$  $\underrightarrow{\triangle}$   $ CaCO_{3}+CO_{2}\uparrow+H_{2}O$

    Z                                      X