Thursday, March 17, 2011
Chemical & Physical Changes of Matter
First light the candle & have them observe it for several minutes. Have them list the changes that they see take place in the candle. (Part of the wax became liquid, it got smaller, etc.)
Next hold the glass plate about 3-4 inches above the flame & have them record what they observe. (If you have enough moisture in the air you will see water droplets form on the plate. Unfortunately, this did not work for us...our air must be too dry this time of year!) If it does work for you, explain that when the hot air hit the cold plate heat was removed from the air. The water vapor in the air then changes to liquid.
Now, being very careful, hold the glass plate just above the flame for a short time. Have them record what they observe. (The plate should become blackened....white plate works best.) Explain what these results show: Even if the candle burns down & appears to get smaller, matter is not lost. It changes into another material...the black substance. At first my son thought the plate was burnt but I showed him that actually the black could rub off & therefore there was no change to the plate...so where did the black come from? It was the candle in a different form.
Have your child list all the changes that occured & label them ch (chemical) or ph (physical). HINT: Wax to liquid - ph, wax burned - ch, vapor to water - ph, plate blackened - ch.
This is a very simple experiment but really gives them a visual of the physical & chemical changes that take place all around them every day.