Question

A white amorphous powder A on heating yields a colourless, non-combustible gas B and a solid C. The latter compound assumes a yellow colour on heating and changes to white on cooling. C dissolves in dilute hydrochloric acid and the resulting solution gives a white precipitate with K₄Fe(CN)₆ solution. 'A' dissolves in dil HCI with the evolution of gas. which is identical in all respect with 'B' The gas 'B' turns lime water milky, but the milkiness disappear with the continuous passage of gas. The solution of 'A' as obtained above, gives a white ppt 'D' on the addition of excess of NF₄OH and passing H₂S. Another portion of the solution gives initially a white ppt 'E' on the addition of NaOH solution, which dissolves on further addition of base. Identify the compounds,A, B. C, D and E,

Answer 1

 (i) The compound 'C'produced by heating 'A' is white in colour and changes to yellow on heating, thus compound 'C' may be ZnO. 'C' with dil HCI and K₄[Fe(CN)₆] gives white ppt. This confirms that the compound 'C' is ZnO

(ii) The gas 'B' turns lime water milky and rnilkiness disappears with the continuous passaqe of gas. Hence. the gas is CO₂ and compound 'A' is ZnCO₃.

(iii)The solution of 'A'gives white ppt of ZnS 'D' with NH₄OH and excess of H₂S.

(iv) The solution of I also gives initially a white ppt. 'E' with NaOH, which dissolves in excess of NaOH.