Cool Science in Seconds: Help! The Apples are Browning!

Have you ever wondered why a cut slice of apple will turn brown after some time? How do you slow down the browning of apples?


Equipment:
- An apple
- Half of a lemon
- 2 shallow bowls
- A knife


Steps:
1. Peel and slice an apple.
2. Leave a slice of apple in a shallow bowl, exposing it to the air.
3. Sprinkle the juice of half a lemon on the second slice of apple and place it in a shallow bowl, exposing it to the air.
4. Wait for about an hour and then compare the appearances of the two slices of apple.


Observation:
The slice of apple that is immersed in water turns brown while the other slice does not.

Image taken from http://www.nsapples.com/teacher/t5schem.htm

Teacher Serena's Explanation:
When an apple is cut open, the enzymes and other chemicals inside the apple combine with oxygen from the surrounding air to form a brown coating. This process is known as oxidation.


When we add lemon juice or another acid to the surface of the sliced apple, we are reducing the amount of oxygen reaching the apple, thus slowing down the oxidation process. Moreover, lemon juice is acidic and lower the pH of the apple, causing the enzymes to become less active.

Watch this video and observe the results.