Question

A chemical reaction is generally accompanied by certain external indications or characteristics. These include – change of – (a) colour (b) state (c) smell (d) evolution of gas (e) formation of precipitate (f) evolution or absorption of heat. With reference to change of colour – state the change in colour seen when the following are heated – zinc carbonate.

Answer 1

Change of colour — In certain chemical reactions a change of colour is seen to be observed. Heat on substances to observe change in colour of reactants and products.

Heat on:

Zinc carbonate ZnCO₃ → ZnO + CO₂ [g]

Colour change:

Zinc carbonate [ZnCO₃] – White – to Zinc oxide [ZnO] – Yellow (when hot)