evolution of a gas

Take a pinch of sodium carbonate (washing soda) in a test tube (15 mL). Add to it a little amount of dilute hydrochloric acid. You will notice that as the two substances mix with each other, effervescence starts. It is due to the production of a gas during the reaction. Sodium carbonate and hydrochloric acid produce carbon dioxide gas, which tries to escape from the test tube. This chemical reaction is, thus, characterized by the evolution of a gas.

change of color

Take a few crystals of potassium permanganate in a test tube. Add a little water to it and shake the test tube until the crystals get dissolved. You will get a dark brown solution. Now, using a dropper, add lemon juice to the dark brown solution of potassium permanganate drop by drop. You will notice that with the addition of each drop of lemon juice, which contains citric acid, the color of solution goes on fading. A stage soon comes when the brown color of the permanganate completely disappears. This chemical reaction is, thus, characterized by a change of color.

formation of a precipitate

Take 5 mL dilute solution of barium chloride in a test tube (15 mL). Now add about 5 mL of dilute sulphuric acid to the solution. You will notice that the mixture becomes turbid. Soon a white colored precipitate settles down at the bottom of the test tube. This chemical reaction is thus characterized by the formation of a precipitate.

change of state

Take a candle and light it. Hold a funnel (with a tube) over the flame as shown in Fig. Pass the gas through limewater. You will notice that litnewater turns milky indicating the presence of carbon dioxide Extinguish the candle and observe the funnel. You will notice water droplets on the inner surface of the funnel. In this reaction, solid wax has been converted into liquid water and gaseous carbon dioxide. This reaction is, thus, characterised by a change of state.