Do this outside and wear safety glasses.
Chemistry, sodium bicarbonate and white vinegar.
Test the pH of distilled water, it should be 7.0. Then add bicarb or vinegar.
Sodium bicarbonate influences the pH of water and will increase the pH to levels above 9.0 if you add enough.
Vinegar is acidic and has a pH around 3.0. This can lower the pH.
If you have 5 phials of water and add bicarb to one and vinegar to the other. Leave the other 3 phials with just distilled water in. Then add some Bromothymol Blue (pH indicator solution available from any pet shop) to each phial. The 3 phials with water only will go green. The phial with bicarb will turn blue. The phial with vinegar will go yellow. Then add a bit of bicarb to the phial with vinegar. Add a couple of drops of vinegar to the bicarb phial. Add bicarb to one of the green water phials and vinegar to another green water phial. Watch the colours change.
---------
If you mix sodium bicarbonate and vinegar together, it goes woosh. You can make a bottle rocket out of vinegar and bicarb. Partially fill a plastic drink bottle with vinegar, put some bicarb in a thin paper bag and put that in the bottle but not in the actual vinegar. Drill a small hole in the lid. Put the lid on the bottle and put your finger over the hole. Turn bottle upside down and shake hell out of it until the bicarb is released from the bag. Then step back.
---------
Make a volcano out of paper mache. Add some bicarb to the center of the volcano and put a couple of drops of vinegar on it. You can mix some red or orange food colour into the bicarb, then you get red or orange lava foam.
-----------------
For a longer experiment in Biology, they can culture green water, infusoria or Daphnia. The following link has info on how to do it. They can use a magnifying glass or microscope (if they have one) to look at the little creatures.
STARTING OUT Make sure you have a pair, (1 male + 1 female). There is nothing worse than spending your hard-earned dollars buying a couple of fish to try and breed and ending up with a pair of fish of the same sex. Let's face it, to reproduce fish you need a male and a female. Two males won't do...
www.fishforums.net