Curious about oxidation?
Today we’re going to use a commonly found, delicious snack: apples, as we explore the process of oxidation.
Have you ever noticed that apples begin to turn brown a few minutes after cutting them up? This is oxidation in action.
Read on as we explore how this happens and what you can do to an apple to stop the browning process!
What is Oxidation?
Oxidation is a chemical process that takes place when a substance comes into contact with oxygen or another oxidizing substance.
Oxidation is why apples turn brown after being cut open.
The skin on the apple protects it, but when it is cut open, the inside of the apple becomes exposed to the air. The oxygen in the air causes a chemical reaction to occur called “oxidation,” resulting in the brown colour we see.
Materials
- Apple
- Knife or apple slicer
- Cups (as many as different liquids you choose to use)
- A selection of liquids, we recommend using the following liquids but you can choose to use fewer or more different liquids
- Water
- Sugar water
- Salty water
- Lemon juice
- Vinegar
- Apple juice
- Tablespoon
- Paper
- Writing utensil
How to Do the Oxidation Experiment
Step 1
With the help of a parent, cut the apple into slices.
Step 2
Prepare the liquids if they are not already pre-made. To create the salt water, stir a spoonful of salt into a glass of water. To create the sugar water, stir a spoonful of sugar into a glass of water.
Step 3
Pour the same amount of each liquid into separate cups.
Make a prediction! What do you think will happen to the apple slice in each liquid? Jot down your predictions!
STEM Q for You: In which liquid do you think the apple will turn the most brown? In which liquid do you think the apple will turn the least brown? Why?
Step 4
Place a slice of apple into each cup. Leave the apple slices to soak in the liquids for a few minutes. Be sure to leave one apple slice out and not in any liquid.
STEM Q for You: Why is it important to leave one apple slice out, not in any liquid?
Answer: Whenever you are conducting an experiment it is important that you have something called a “control” to compare against. In this experiment, we want to compare each of the apple slices soaked in different liquids to a regular apple slice to see how each liquid affects the browning process!
Step 5
Take the apple slices out of the liquids and place them onto the piece of paper. Label each apple slice with the liquid it soaked in. Label your control apple slice as well.
Step 6
Leave the apples on the paper for about five minute. After five minutes have passed record your observations! What happened to each of the apple slices?
Try out each of the apple slices, do they still taste good?
Was your prediction correct? In which liquid did the apple slice turn the least brown?
Vinegar and lemon juice both should have been effective in preventing the apple slices from turning brown! This is because vinegar and lemon juice are both very acidic.
Why Does Lemon Juice Stop Apples From Turning Brown?
Lemon juice is acidic because it contains a compound called ascorbic acid which helps to stop the oxidation process from occurring! Additionally, lemon juice contains something called “antioxidants” which help to counteract the oxidation process.
Together this makes lemon juice the best liquid to prevent apples from browning, and it tastes the best too!
What Causes Oxidation to Happen?
The inside of the apple contains a chemical enzyme called polyphenol oxidase (PPO for short). When the inside of the apple becomes exposed to the air, it activates this PPO enzyme to begin breaking down other parts of the apple’s tissue, turning them brown.
What is an Enzyme?
An enzyme is something that causes a chemical reaction to happen very quickly.
In order to prevent an apple from browning, we must slow down the reaction that the enzyme is causing to happen.
We can slow the reaction down by either making the PPO enzyme less reaction or prevent it from having things to react with. Lemon juice does both!
