Question

A reddish brown vessel developed a green coloured solid X when left open for a long time When reacted with dil $H{}_{2}SO{}_4$ (sulphuric acid) it forms a blue coloured solution along with brisk effervescence due to colourless and odourless gas Z .X decomposes to form a black coloured oxide Y of a reddish brown metal along with gas Z Identify X Yand Z

Answer 1

• The vessel of copper has a reddish brown colour when left in the open air and combines with carbon dioxide and moisture present in the air to form a green-coloured coating called copper carbonate which is basic in nature.
• Hence, X is copper carbonate $CuCO{}_3$
  
• When this green-coloured copper carbonate reacts with concentrated sulfuric acid it forms a blue-coloured solution of copper sulfate ($CuSO{}_4$) and a colourless and odourless gas carbon dioxide ($CO{}_2$) also evolved.
• $CuCO{}_3+H{}_{2}SO{}_4⟶CuSO{}_4+CO{}_2+H{}_{2}O$
  
• When copper carbonate undergoes decomposition it forms a black-coloured oxide known as copper oxide which further decomposes to give carbon dioxide.
• $CuCO{}_3⟶CuO+CO{}_2$
  
• Hence, Y is copper oxide and Z is carbon dioxide gas.
• The chemical equation for the reaction is following:

$2Cu+2H_{2}O⟶2CuO+2H_2$