While we learn about physical changes, we
will see what happens when copper sulphate is heated, how it changes its colour and then gets back to its original colour. Let’s see what we need to perform this experiment. First, I will first fix the test tube to a tong. Now, we will add some copper sulphate crystals into the test tube. Do you know the colour of copper sulphate crystals? Copper sulphate crystals are blue in colour. We will now have to heat this test tube. We just lighted the spirit lamp purpose. Now, let’s heat up the copper sulphate which is blue in colour and observe what happens. It was in blue colour. Now notice what happens. Colour sulphate is releasing its water content. The blue colour copper sulphate is turning white. It has turned white because it’s water content has evaporated. We will now put the white copper sulphate into a Petri dish. How has it changed? It has changed to almost white in colour. Let’s keep this away and see what happens next. It is white in colour right? Let’s see if it will get back its original colour. When will it get back its original colour? Water has evapourated therefore let’s add some water. It has changed to blue colour again. It means there was only a change in its colour. There was no change in its composition. This is what we call physical change. We keep seeing such physical changes all the time. Most common example is ice. Ice is in solid state. When ice melts, it becomes water as is in liquid state. What will happen when we heat this liquid heated? It becomes steam. When steam is cooled, it changes to liquid state. When it is frozen, it comes back to solid the state. Hope you have now understood what we mean by physical changes now. Now, we will write this equation on the board.