i did a single displacement experiment using surface area as the independent variable. i used a copper (II) nitrate solution, and used powdered zinc, powdered nickle, and small pices of aluminum, as well as larger versions of each of the aforementioned elements. according to the activity series, they all should have reacted, but only zinc did. aluminum and nickel, in either of their forms, failed to react. does anybody know why this may have happened?