Give 1 example which illustrates the following characteristics of a chemical reaction

(I) evolution of gas

(II) change of colour

Reaction involving evolution of gas.

• A replacement reaction concerning zinc metal and hydrogen chloride:

Zn + 2 HCl → ZnCl2 + H2 (gas) In this example, hydrogen gas in diatomic form is released.

• A replacement reaction where gaseous hydrogen chloride and fluorine gas react to release diatomic chlorine gas (because fluorine is more electronegative):

2 HCl + F2 → 2 HF + Cl2 (gas)


Change in color--- Reaction between citric acid and purple colored potassium permanganate solution gives colourless solution.