Science Buddies: "Ask an Expert"

I did an experiment on what Ph level of bleach corrodes pennies. The Ph level of household bleach without anything in it has a Ph level of 10. I did 1 hour increments up to 5 hours with a penny in a cup of bleach and the ph level did not change and the pennies had very little corrosion. I kept one penny in a cup of bleach overnight and the Ph level the next morning was 7 and had the most corrosion. I thought that the Ph level would be higher with a higher level of corrosion. Can you tell me why it would have a lower Ph level? thank you.

The pH level of bleach should be around 12. My best guess as to what you problem is is that you had old bleach. Was this some bleach that was sitting around the house, or did you buy new?

The type of chemical reaction involved is an oxidation/reduction reaction. The fact that the pH of your bleach solution decreased over time is an indication that it is being depleted (used up).

The rate of reaction will depend on the amount of exposed surface area, how oxidized the copper is to begin with or if there is some oil or other substance that will keep the bleach from reaching pure copper, and the initial pH of the solution, and the temperature.