Activity 9.2 Let us experiment (Demonstration Activity) (Page 137) Class 8

Activity 9.2 Let us experiment (Demonstration Activity) (Page 137) Class 8

Activity 9.2 Let us experiment (Demonstration Activity) (Page 137) Class 8

Take about 50 mL of water in a glass beaker and measure its temperature using a laboratory thermometer, say 20°C. Add a spoonful of baking soda (sodium hydrogen carbonate) to the water and stir until it dissolves. Continue adding small amounts of baking soda while stirring, till some solid baking soda is left undissolved at the bottom of the beaker. Now, heat the contents to 50°C while stirring.

1. What happens to the undissolved baking soda? Class 8

Answer:

We observe that it has dissolved.

2. Continue adding more baking soda while stirring at this temperature until some solid baking soda remains undissolved. Again, heat the contents further to 70°C while continuing to stir. What do you observe? Class 8

Answer:

1. The undissolved baking soda dissolves.
2. Water at 70°C dissolves more of the baking soda than at 50°C.

3. What do you infer from this experiment? Class 8

Answer:

1. It is inferred that for most of the substances, the solubility increases with temperature.
2. A saturated solution becomes an unsaturated solution at a higher temperature.