Foods produced the first acids that people experimented with. Acidic foods taste sour. In Latin, acid or "acere," means sour, the Visionlearning website says. Acids also corrode metal. Bases you encounter in everyday life are soaps. Chemically, acids have a hydrogen ion available to lend to a reaction while bases, a compound that reacts with acids, can capture hydrogen atoms. When you mix an acid and a base, you get a salt and a molecule of water.
Not all juices are acidic. Carrot juice, for example, is relatively neutral. And those juices with acid don't all have the same acids. Citrus fruits have citric acid, apples have malic acid and pomegranates have ellagic acid. Choose a variety of fruit or vegetable juices to test abilities to clean pennies. A well-rounded selection might include lemon, apple, grape and carrot juices.
You will get better results for your project if you squeeze the juice yourself. Juice that you buy in containers isn't just juice. If you read the ingredient list on the side of the container, they often contain additives, including salt, which can have an effect on the outcome of your experiment. In addition, the juices are often either concentrated or reconstituted from concentrates. Not knowing the juice concentration makes predicting the results of your experiment difficult.
When doing a project where you are making a judgment about the outcome, one measurable result you can record is time. Let's say that apple juice cleans a penny in an hour, but carrot juice only takes 12 minutes. If you don't look at the penny until the next the end of the hour, they both will seem to have the same effect. Instead, check on the pennies frequently until you see how fast the juices are cleaning them. If it's going slowly, you can look at the pennies less often.