When conducting science experiments, pH paper is sometimes used to determine how acidic or basic a substance is based on its color change. How do the colors change in the first place and how is it a reliable indicator to identify the acidity of a substance? How can you make your own experiments using pH paper at home? Read to find out!
The pH Scale
pH, which stands for potential hydrogen, is a measure of the number of H+ (hydrogen) ions there are in a substance, which determines its acidity. If the substance has a high concentration of H+ ions, it is classified as an acid, and if it has a low concentration of H+ ions, it is classified as a base. Some examples of common acids are citruses and vinegars while some common bases are toothpaste and baking soda.
Since there is a range of different potential ratios between these two H+ ion concentrations, the pH scale is used to measure how acidic or basic a substance is. This scale ranges from 0 to 14; 0 being the strongest acids and 14 being the strongest bases. In some cases, the ratios between these two H+ ion concentrations may be equal, and the substance is classified as neutral, its pH being a 7 on the scale.
When a pH strip goes into contact with a substance, it changes color. This color corresponds to a number or range of numbers on the pH scale that will determine the acidity of the substance.
How Does the Color Change Work?
Strips of pH paper are coated with flavin, which is a chemical that dissolves in water and changes color in varying types of substances. When the strip turns red, it indicates an acidic solution while bluish-green indicates a basic solution. The scale resembles a rainbow, which indicates how strong/weak an acid/base is.
Experiments with pH Paper (from ScienceBuddies): Making Your Own At Home!
To make your own pH paper at home, you'll need:
red cabbage leaves
water
cooking pot/stove
strainer (optional)
Procedure:
Cut the cabbage leaves into 1-inch slices.
Put it in a cooking pot and pour a small amount of water to cover the top of the leaves.
For half an hour, cook the leaves in a stove at medium heat.
Afterwards, remove the leaves from the heat and leave it to cool.
Pour the liquid out to separate the paper and the liquid. (You can use a strainer to make this easier.)
Using the liquid acquired, soak several sheets of filter paper in the cabbage water for half an hour. (Although the water is blue right now, it will change color later on when used on different substances.)
Drain the liquid, then allow the filter paper to dry overnight.
Cut the filter paper into strips. They are now ready to test the pH levels of different substances!
Experiments:
You can test the acidity of different solutions in your house using the pH paper. For instance, some substances you can use to test include lemon juice, vinegar, orange juice, soda, bananas, milk, eggs, soapy water, and anything else you want!
Compare the color changes you observe with a pH scale and learn about what substances are classified as acids and bases as well as how strong or weak each one is. Have fun exploring!
Written by: Janice Le
Resources:
Bio-Resource. “How Does PH Paper Work?”YouTube, uploaded by Bio-Resource, 1 Jan. 2015, www.youtube.com/watch?v=pbVNcp9Fekw.
JacobL. “Acids & Bases Found in Homes.”Sciencing, 18 Nov. 2019, sciencing.com/acids-bases-found-in-homes-12003805.html.
Science Buddies Staff. "Make Your Own pH Paper."Science Buddies, 13 Mar. 2020, https://www.sciencebuddies.org/science-fair-projects/project-ideas/Chem_p041/chemistry/make-your-own-ph-paper. Accessed 4 June 2020.
Taylor, Somer. “How Does PH Paper Work?”Sciencing, 2 Mar. 2019, sciencing.com/ph-paper-work-4923429.html.
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