Home Experiments With Acids and Bases
The pH scale is the measurement of how acidic or basic a substance is. It specifically measures the amount of free hydrogen ions found in a solution. Although it sounds contradictory, substances with a low pH (below 7) have more free hydrogen ions and are considered acids. Solutions with a high pH (above 7) have little free hydrogen ions and are considered bases. If a substance has a pH of 7, it is considered neutral. So why should we care about pH?
The pH of substances plays a very important role in the chemistry of various systems all around us. In order to obtain nutrients like Phosphorus and Nitrogen, most plants need to grow in slightly acidic soils (pH of 5-7) to easily obtain these nutrients. Seawater is slightly basic (pH of 7.5-8.5) making it easy for many marine invertebrates like snails and corals to build calcium-based shells. pH plays some very important roles within our bodies. Highly acidic gastric acid (pH of 1.5-2) helps breakdown food, specifically proteins, in our stomach. Carbon dioxide buildup in deoxygenated blood makes it more acidic and when exposed back to oxygen, makes the blood more basic and facilitates gas exchange in our lungs. Many different cleaners work so efficiently, based on their pH and how they react to different stains and substances.
There are some great experiments to test out pH. Some are quick while others may take a few days to weeks. Here are some great experiments with household items!
Often in chemistry experiments, we want to have an indicator. Indicators allow us to see if a chemical reaction has occurred by changing a physical characteristic (color, smell, temperature, etc.). Red cabbage juice is a great indicator of changes in pH! This is a fun activity to do with children, though they should always be supervised with any chemicals. Here’s how to do the experiment:
- Chop up half a red cabbage and place it in a pot with 6-8 cups of water.
- Heat the water and cabbage on a stove until the water is just about to boil.
- Strain the cabbage from the water. You’ll notice that the water has turned purple. You’ll need this purple water for the next steps.
- Find some kitchen acids and bases. Some great and common acids that you can use are clear soda (Sprite, Sierra Mist, etc.), lemon juice, vinegar, green tea, and milk. Some great and common bases include baking soda, milk of magnesia, and dish soap. Bleach, ammonia, and lyme can also be used as bases but only with an adult and should be diluted a little before the experiment.
- Pour the different acids and bases in clear cups about half way. It is best to put them in order from most acidic to most basic. Always use gloves and eye protection when dealing with chemicals.
- Test it! Pour some cabbage juice into the cups with the different chemicals. You should see a color change within 10 seconds. Once the chemical reaction has occurred, you can use the pH scale below to see what the pH of the different chemicals was.
What do sea snails, oysters, and corals all have in common? They are all marine invertebrates! That means that they don’t have an internal skeleton like people do. Instead they have a hard shell made up of calcium carbonate to protect them. However, if sea water (which has a pH of about 7.5-8.5) becomes more acidic, it can prevent them from building their shells. In extreme cases, it may even dissolve them! In order to see this, follow these steps:
- Find an oyster, snail, or clam shell. Pick one that is broken or you don’t like.
- Create an ocean. You will need a clear cup of water and place half a teaspoon of salt in the cup. Mix until salt has dissolved.
- Next, place your shell in the cup.
- Now, it’s time to lower the pH like an acidic ocean. Add a half cup of vinegar to the cup.
- Take a before and after picture to compare what happens to the shell. You should see the shells dissolve within a day or two.
Spring is the perfect time to do this experiment! Hydrangeas (Hydrangea macrophylla) are also good indicators of pH. When you go to your local greenhouse, you may see them in a variety of colors including pink, blue, and purple. Usually when you see different colored flowers on plants, it means that they are different varieties. However, hydrangeas can change the color of their flowers based on the pH of the soil. Here’s how to do it:
- Obtain three hydrangea plants, preferably before they bloom. To control the pH of the soil, you will want to keep them in pots.
- The first pot is going to be the basic soil which creates beautiful pink flowers. In a gallon jug, add a half cup of baking soda and fill with water. Apply the water treatment to the hydrangea once every 2-3 days.
- The second pot is going to be the acidic soil which creates rich blue flowers. Place a three inch piece of aluminum foil at the base of the plant. In a gallon jug, add a cup of lemon juice and fill with water. Apply the water treatment to the hydrangea once every 2-3 days.
- The last pot is going to be the neutral soil (a pH of 7) which creates striking purple flowers. Place a two inch piece of aluminum and water every 2-3 days.