Acid Rain Demonstration
Students learn how acid rain is formed and the use of pH indicators.
This experiment involves burning matches to produce sulfuric acid, which is captured in a beaker to demonstrate acid rain formation. Red cabbage juice is used as a natural pH indicator to visualize the change in pH.
What You Need
Acid Rain Demonstration
- Large, 1L beaker
- Water
- Red cabbage juice (10 mL)
- Wooden matches
- Tape
- Glass cover for breaker
To prepare the red cabbage juice:
- Red cabbage
- Blender or food processor
- Water
- Mason jar or airtight container
Activity Guide:
Safety Notes
Ensure you are familiar with Let's Talk Science's precautions with respect to safe virtual outreach to youth.
Inform the educator prior to the event that this activity requires the use of matches. Keep matches with you at all time, do not leave on bench.
What To Do
To prepare the cabbage juice
- Remove the outer leaves of the red cabbage and discard.
- Tear up the red cabbage leaves into smaller chunks and place in the blender or food processor. Use mostly the leafy part of the red cabbage and less of the stems.
- Fill the blender or food processor to approximately 3/4 full of leaf chunks.
- Add water so that all the leaf chunks are submerged. Don't add any extra water on top of that.
- Let soak for 15 minutes.
- Blend until all large chunks are in an airtight container to use in the experiment. Discard the blended bits of cabbage.
- You should have approx. 300mL from one blender.
- Keep the red cabbage juice refrigerated until the day of the activity.
Demonstration
- Fill the beaker with 100mL of water, enough to see the liquid at the bottom of the beaker.
- Bunch the matches together and tape them (leave one of two out to use to light the torch you've created). Tape the ends of your torch to the inside of the beaker, approx. 1/4 to 1/3 down from the top of the beaker.
- Show this set-up to the students and explain it is just water at the bottom of the beaker.
- Add cabbage juice so you can clearly see the colour. Allow students to make observations.
- Hold the beaker over a sink for the remainder of the demonstration.
- Light your torch and cover the beaker as quickly as possible. With the beaker on the lab bench, hold the lighting match in one hand and the cover in the other or get another adult to hold the cover. Light your match and reach into the beaker to light one piece of the torch. Once one piece is lit, the rest will light too.
- Cover the beaker with the glass cover. You want to capture as much smoke as possible. Once the cover is on you may hold up the beaker for students to see. The best way to hold it is one hand close to the bottom of the beaker and one hand holding the glass cover near the top.
- Once the fire has stopped, while keeping the cover on, swirl the solution at the bottom of the beaker. You are trying to mix the water and smoke as much as possible.
- Ask students: Why does the water and cabbage juice change colour?
- At the end of the demo, run all matches under water to ensure they are out.
Discovery
There is sulfur in the match tips that is released into the air when they burn. This sulfur reacts with air molecules to create sulfuric acid. Sulfuric acid is acid rain!
pH is a measurement of a number of small molecules called hydrogen ions (H+) in a liquid. If you have a lot of H+, you will be at the low end of the pH scale and be very acidic. If you have fewer H+, you will be on the high end of the pH scale and be very basic. An acid/base indicator is a chemical that changes colour when an acid or base is present in a liquid. Red cabbage juice is a natural pH indicator - it will turn pink in the presence of an acid and blue in the presence of a base.
What's Happening?
There is sulfur in the match tips that is released into the air when they burn. This sulfur reacts with air molecules to create sulfuric acid. Sulfuric acid is acid rain!
pH is a measurement of a number of small molecules called hydrogen ions (H+) in a liquid. If you have a lot of H+, you will be at the low end of the pH scale and be very acidic. If you have fewer H+, you will be on the high end of the pH scale and be very basic. An acid/base indicator is a chemical that changes colour when an acid or base is present in a liquid. Red cabbage juice is a natural pH indicator - it will turn pink in the presence of an acid and blue in the presence of a base.