Questions to investigate for Chemistry projects:

Countertop Chemistry Investigations to try.
UV rays and everyday objects

You know that you should wear sunscreen when outdoors because of the UV rays. So what would these rays do to rubber, or ink or paper? What about photographs or documents?
Vinaigrette V. S. Coca Cola
If you have watched someone make an oil and vinegar salad dressing, you will have undoubtedly noticed that the oil and vinegar separate after a while. Does this happen to some other liquid made up of different substances? How about Coca cola - would it ever separate into it's constituent parts?
Surface Tension
Different liquids have different surfaces tensions. Does the tension of water go up or down when soap is added? How might this affect certain insects that run on the surface of ponds?
White powders
How do scientists tell the difference between baking soda and flour or salt and sugar?
Fire and Foam
Why do firefighters sometimes use a fire-retardant foam to fight fires instead of water? Why don't they always use foam (or water?)
Can you get pure water from salt water? How would you do it? Why don't we get all of our fresh water from the ocean? This is a good middle school science project with plenty of room for personalization.
Hair Chemistry - How do hair styling products work?

Cheyenne, from New Zealand, did her science fair project on the quality of drinking water - she tested for pH, chlorine, copper, iron, bacteria and 'hardness'. Here is her blog and a video that she recorded:**