Use litmus paper to test the acidity of lemons and limes to see which one is the most acidic. Find litmus paper at a science supply store or you can purchase it from different online sites. The litmus paper strips come in red and blue. Use the blue strips to test for acidity. The pH scale runs from 0 to 14, with 0 being the most acidic. The amount of the color change that occurs tells you how acidic a substance is.
To test the acidity level of the lemons and limes, squeeze out some of the juice into a cup. Do not add water or any other substances to the citrus juice. Dip one of the blue pieces of paper into the lemon juice and then dip another into the lime juice. If the substance is an acid, the blue paper will turn red where it touched the liquid. Test the red paper strips as well, although the red is for testing bases. Because the red is for testing bases, the paper will probably not change color.
Test other liquids around your home to see how they compare to the lemons and limes. Ask your parents to make sure that it is okay to test certain things, especially household cleaners. It may be a good idea to wear goggles to protect your eyes during your experimentation. Good liquids to test include dish soap, vinegar, fruit juice, soda, water and milk.
If you cannot find pH strips for purchase you can make your own using red cabbage and coffee filter papers. Cut up a head of red cabbage into 1-inch pieces and cover with water. Simmer on medium heat for about 30 minutes. Allow the cabbage to cool and then pour off the water into another bowl where you will soak the coffee filters for 30 minutes. Spread the coffee filters out on a towel to dry and then cut into strips about 1 inch wide. Use these strips to test your lemon and lime juice to see if they are acidic. If the paper changes color than your substance is an acid. If it does not change color, then your substance is a base.