Question

Identify the salt P from the following observation.

Salt P has a light bluish green colour. On heating, it produces a black-coloured residue. Salt P produces brisk effervescence with dil. HCl and the gas evolved turn lime water milky, but there is no action with acidified potassium dichromate solution.

Answer 1

Observations:

• Light bluish-green colour indicates the presence of Copper (Cu²⁺) ions.
• Heating produces a black residue of copper(II) oxide (CuO).
• Brisk effervescence with dil. HCl that turns lime water milky but has no action on acidified potassium dichromate confirms the gas is Carbon dioxide (CO₂), meaning the anion is a Carbonate \[\ce{(CO^{2-}3)}\].

Chemical Equation:

\[\ce{\underset{Light bluish green}{CuCO3} ->[\Delta] \underset{Black residue}{CuO} + \underset{Turns lime water milky}{CO2 ^}}\]

Salt P is Copper carbonate (CuCO₃).