(a) Name the residue obtained on… | Chemistry

Question 1 Report

(a) Name the residue obtained on strongly heating the following:

(i) ZnCO\(_3\) in an open crucible;

(ii) CuSO\(_4\), 5H\(_2\)O and then allowing it to cool in a desiccator.

(b) State the colour changes observed on heating and cooling in each case in(a) above.

Answer

Answer Details

(a) Residue on strong heating:

(i) ZnCO₃ in an open crucible decomposes to give zinc oxide (ZnO) as the residue: \(\text{ZnCO}_3 \to \text{ZnO} + \text{CO}_2\).
(ii) CuSO₄·5H₂O loses its water of crystallisation to give anhydrous copper(II) tetraoxosulphate(VI), CuSO₄: \(\text{CuSO}_4\!\cdot\!5\text{H}_2\text{O} \to \text{CuSO}_4 + 5\text{H}_2\text{O}\).

(b) Colour changes:

(i) ZnO: white when cold, turns yellow on heating, and returns to white on cooling.
(ii) CuSO₄·5H₂O: the blue hydrated crystals turn white (anhydrous CuSO₄) on heating; on cooling in a desiccator it stays white (it would turn blue again if water is added).

(a) Name the residue obtained on strongly heating the following: (i) ZnCO\(_3\) in an open crucible; (ii) CuSO\(_4\), 5H\(_2\)O and then allowing it to cool...