Acids vs. Bases: Cleaning Pennies Experiment

Purpose: The purpose of this experiment is to find out which of four household products can most effectively remove tarnish off of pennies. Furthermore, the four products have been chosen based on their acid/base Ph level, which should yield information on which is better for the cleansing of pennies.

Hypothesis: The hypothesis of this experiment is that the stronger the acidity of the solution, the better it will remove the tarnish off pennies. The rational is that tarnish is a sign of oxidation, whereas, acids release H+ and ion which will combine with the oxidation on the pennies, and therefore remove the tarnish, whereas, bases remove H+ from a solution, and henceforth, will have little effect on the pennies.

Pictured above: Equipment used in this experiment, also pictured is Scientific AmeriKen's beverage of choice.

Equipment: The experiment will require 20 tarnished pennies, vinegar, water, baking soda, lemon juice, ammonia, 4 small cups, a stirring rod, a pencil and paper.

Procedure: Into each cup place 5 pennies, in one cup add lemon juice, the next add baking soda and water, vinegar in the net cup, and finally ammonia in the last cup. Shake and stir each of the cups to allow the chemicals to have an effect on the pennies, after 10 or so minutes, remove the pennies from the cups, dry and compare against other chemicals.


Substance added to pennies Ph level Observations
Lemon Juice 2.3 All five of the pennies were restored to their coppery color.
Vinegar 3.0 3 of the 5 pennies were nearly restored to coppery color.
Baking Soda and Water 9.0 No effects were observable on the pennies.
Ammonia 11.0 Most pennies are partially cleaned, ammonia turned blue after process was complete.

Conclusion: The hypothesis was proven true, and the pennies, were best cleaned by the strongest acid, which in this experiment was lemon juice. A questionable aspect of this experiment is arisen with the change of the color of ammonia during the experiment. The blueness of the ammonia might be a coppery solution, as ammonia may have reacted with the copper pennies, but it probably just dissolved the blue dye away from the sides of the dixie cup.

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