02 Heating Substances

TO FIND OUT THE ACTION OF HEAT ON SOME SUBSTANCES Introduction Substances do not behave the same way when heat energy is given to them by means of a Bunsen burner. Some of them will change into others and it will be difficult if not impossible to turn them back to their original state. We call these changes chemical changes. Some others will just melt or boil and will return to the original state once they are cooled down. These undergo physical changes. Others will not be changed (at least at the temperature of the burner). Aims To find out the action of heat on some substances Materials Bunsen burner, spatulas, test tube rack, Pyrex test tubes and test tube holders, copper sulphate crystals, copper carbonate, salt, sand, water, starch, wax. Procedure 1- Fill a test tube (use a spatula) with one of the substances of the list up to 1 cm from the bottom. 2- Hold the tube (by means of a test tube holder) in a blue Bunsen flame for one minute. Be sure the test tube is not pointing to any person in the lab. Keep it tilted to an angle of about 45° to 30°as shown.

3- When heating a liquid never heat it at the bottom but at the upper half of it. It will avoid sudden squirting of hot substances that may burn you or others.

4- Observe what is happening. Write down your results in the table below. 5- Study your results and tell which of the substances has suffered a chemical or a physical change.

Substance heated Name and Appearance

Observations

Physical or Chemical?