In chemistry, we often talk about the pH of various substances, but what exactly does that mean? Let’s find out!
What is the pH Scale?
pH stands for potential for hydrogen. Look at hydrogen on the periodic table. How many protons does it have? How many electrons? Look at a diagram of hydrogen. What do you remember about what atoms like to do with their orbitals? They like to fill the outer ones (called valence shells) up or empty them. Since hydrogen only has one electron, it is a pretty reactive atom! It likes to give an electron or get one, and thereby bond with many different atoms. Potential for hydrogen, or pH, refers to what is happening to hydrogen in a compound.
The pH scale is a scale from 0-14. 7 on the pH scale is neutral. Water has a pH of 7. Anything lower than 7 is acidic – the acidity gets higher as the number gets lower. Anything greater than 7 is a base or alkaline and its alkalinity gets higher as the numbers get higher.
Acids like to give away hydrogen ions. They are sour and they react with metals, so they are corrosive. Acids can also be damaging to living tissue. Bases like to collect hydrogen ions. They are bitter and slippery. They are good at dissolving fats. Because of this, most soaps are basic. A strong base can also be damaging to living tissue.
Let’s do an activity to become familiar with the pH of everyday substances.
For this activity you will need:
8-10 small cups for each child who will do the activity
8-10 different liquids ranging in acidity and alkalinity
a sheet of paper to keep track of your results
Number 8-10 small plastic cups. Gather an assortment of acidic and basic liquids. Some liquids you might use are: tomato juice, soda, orange juice, baking soda water, lemon juice, vinegar, milk of magnesia, dish soap (thin it slightly with water), hand soap (thin it slightly with water), and glass cleaner. Make sure to include water in your assortment. Fill each cup halfway with one of the liquids. Be sure to keep a numbered list so that you know what liquid is in which cup.
Have the children test the pH of each liquid with the end of a litmus strip. Compare the color on the strip to the pH scale that comes with your litmus strips. Which of the liquids is the most acidic? Which is the most basic? Can you guess what each of the liquids is? Have the children record their results!