High School Corrosion Projects

Here are some ideas:

Weight loss testing of steel in various environments, e.g. vinegar, bleach, ammonia, liquid fertilizer. Easiest form of test samples is "non-galvanized steel nails" purchased from the hardware store.
Effect of salt concentration on corrosion rate of steel in stagnant and aerated solutions. Comparing corrosion "rates" of steel, copper, galvanized steel, stainless steel (e.g. nails) in tap and river water, vs outdoor atmospheric exposure etc.
Demonstrating how galvanic coupling of dissimilar metals increases corrosion rate of one metal and reduces corrosion rate of the other metal.
Corrosion of carbon steel in various environments. Nails are sanded to a bright metal finish, washed with water, dried, weighed, and photographed. Then they are hung in various solutions (distilled water, vinegar, salt water) with and without exposure to air. 8 ounce glass jars with screw-top lids will do. A fish tank aerator pump and air diffusers can be used to bubble air through half the bottles while keeping the others tightly closed. Make photographs at different time intervals, then cleaned and weighed them to determine the weight loss after ~2 months. The weight loss per unit area from the data can be tabulated.
A series of experiments on rusting

In all cases, it is important to emphasize the importance and use of multiple samples (e.g. nails) so that they also learn about statistics in analyzing data such as the mean of the results, their range, and standard deviation.