Fill a drinking glass halfway with water.
Carefully drop an egg in the water. The egg is going to sink, so be very gentle. Discuss with your child why she thinks that the egg dropped to the bottom of the glass.
Pull out the egg carefully with a spoon.
Add 6 tbsp. of salt to the water and mix well.
Add water to the glass until it is almost full. Be careful not to pour the water in the glass with such force that the saltwater and plain water combine.
Lower the egg into this glass of water. Notice how the egg now floats.
Ask child why she thinks that the egg floated this time. The term "density" can be mentioned to older children. Younger children can just be told that the salt makes the water a little heavier.
Squeeze the juice from a lemon and put it aside.
Stretch out a balloon.
Add 1 tsp. of baking soda to the soda bottle and stir well with the straw.
Add the lemon juice to the bottle. You may need a funnel to help you get it into the small opening.
Place the balloon over the mouth of the soda bottle. Watch the balloon blow up on its own. Discuss what you think caused this to happen with your child. Mention the terms "acids and bases" to your older child, and for younger children, explain that the baking soda and lemon juice had a reaction.
Place a penny in a paper cup.
Pour lemon juice over the penny. Be sure that the penny is completely covered.
Leave penny in the lemon juice for five minutes.
Remove penny from cup and wipe dry with a paper towel.
Discuss with your child why he thinks that the penny is now shiny. Expose your older child to the terms "oxidation" and "chemical reaction." Explain to your younger child that the lemon juice has something in it that cleans the pennies.