Question

A black powder when heated with cone. $HCl$ gives a greenish yellow gas. The gas acts as an oxidising and a bleaching agent. When it is passed over slaked lime, a white powder is formed which is a ready source of gas. The black powder and white powder respectively are

• A. $KCIO_3$ and $NaClO_3$
• B. $MnO_2$ and $Ca(OCl)_2$
• C. $MnO_2$ and $KClO_3$
• D. $MnCl_4$ and $COCl_2$

Answer 1

Answer: (B)

$MnO_2$ and $Ca(OCl)_2$

Answer 2

$\underset{\text{Black powder}}{ {MnO2}}+$ $\underset{\text{(conc.)}}{ {4HCl}}$ ${-> MnCl2 +2H2O +}$ $\underset{\text{Greenish yellow gas}}{ {Cl2}}$ ${Cl2 +H2O \to 2HCl +[O]}$ Coloured matter ${+[O] ->}$ Colourless matter $\underset{\text{Slaked lime}}{ {2Ca(OH)2}}+ {2Cl2 ->}$ $\underset{\text{Bleaching powder (white)}}{ {Ca(OCl)2}}+$ ${CaCl2 +2H2O}$