Combining an acid (vinegar) with baking soda (sodium bicarbonate) will cause a dramatic chemical reaction sure to wow the kids. When the two chemicals are combined, carbon dioxide gas is produced and a fizzy mess is made. Take an empty 2 liter soda bottle and place a few tablespoons of baking soda into the bottom. Fill the bottle with 1 cup of vinegar and then quickly place a balloon over the top of the bottle. The balloon will become inflated with the bicarbonate gas that is created from the chemical reaction.
A simple chemical reaction using vinegar and milk will divide ordinary skim milk into curds and whey. Place 4 tsp. of white vinegar into a microwave safe bowl. Add 1 1/2 cups of skim milk to the bowl and then place it in the microwave. Microwave the mixture for 1 minute. Look in the bowl. You will see that the milk has now transformed into two parts: the solids of the milk, called the curd, and the liquid whey. Strain the mixture through a mesh sieve and you will be left with the whey which you can form into a rubber-like glob.
Get visual feedback of the density of different household liquids by creating your own science beaker out of a clear drinking glass. Fill a glass about halfway full with water mixed with a few drops of food coloring. This will allow you to easily see the water in the glass. Slowly pour in a half cup of molasses. The molasses will sink to the bottom because it is heavier, or more dense, than the water layer. Slowly add a few tablespoons of cooking oil to your glass. It will form a layer on top of the water, showing you that it is lighter, or less dense, than the water. You can use other liquids found around the house to test their density as well.
Fill a drinking glass with clear soda and add a small handful of raisins to the glass. The raisins are more dense than the liquid soda, so they start to sink, but the carbon dioxide bubbles in the soda attach to the raisins wrinkles, causing them to float back up. The combined effect causes the raisins to bob up and down, or dance, in the soda. The raisins will continue dancing for about one hour, until the soda loses its carbonation.