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๐ฌ Think about it
Heating or cooling water just changes it between ice, water, and vapour — the particles stay water. But what if we pass electricity through water? Something surprising happens. Let's experiment and find out.
Does water stay the same when heated or cooled?
- On cooling, water turns into ice.
- On boiling, water turns into vapour.
- We can get water back again by heating ice or cooling vapour.
- So the particles of water remain the same throughout.
Example:
Ice in a glass melts back to the same water on a warm day.
In this Activity, we will pass electricity through water and collect the two gases that come out.
Safety first
Perform under teacher supervision. Be careful with sulfuric acid. Do not use a lithium-ion battery. Maintain a safe distance during gas testing.
Materials needed
Two small test tubes, a beaker or glass tumbler, a 9 V battery, water, dilute sulfuric acid, a candle.
Procedure
1. Collect two small test tubes, a beaker (or glass tumbler), and a 9 V battery.
2. Fill two-thirds of the beaker with water and add a few drops of dilute sulfuric acid.
3. Fill both small test tubes completely with water taken from the beaker.
4. Place a 9 V battery inside the beaker.
5. Carefully place the water-filled test tubes on each terminal of the battery, without spilling water.
6. Wait for a few minutes and watch for gas bubbles at both terminals.
7. Let it continue for 10–15 minutes and observe the gas volume in each test tube.
8. Remove the test tubes one by one carefully.
9. Bring a burning candle near the mouth of each test tube to test the gas.
2. Fill two-thirds of the beaker with water and add a few drops of dilute sulfuric acid.
3. Fill both small test tubes completely with water taken from the beaker.
4. Place a 9 V battery inside the beaker.
5. Carefully place the water-filled test tubes on each terminal of the battery, without spilling water.
6. Wait for a few minutes and watch for gas bubbles at both terminals.
7. Let it continue for 10–15 minutes and observe the gas volume in each test tube.
8. Remove the test tubes one by one carefully.
9. Bring a burning candle near the mouth of each test tube to test the gas.
Observation
Gas bubbles form at both terminals. The two test tubes collect different volumes of gas. One gas gives a "pop" sound (hydrogen); the other makes the flame glow brighter (oxygen).
Explanation
These gases are not water vapour — otherwise they would condense back to water. Water is made of two different constituents, hydrogen and oxygen. Passing electricity splits water into these two gases.
โ Summary
- Electricity passed
- Two gases collected
- Pop = hydrogen
- Brighter flame = oxygen
What did splitting water tell us about it?
- Water is composed of two different constituents.
- These are hydrogen and oxygen.
- So water can be broken into simpler substances.
Water Splits into Two Gases
Water
↓
Pass electricity
Electric current breaks the water down.
↓
Hydrogen + Oxygen
๐ก Ever heard of ...
- Electric current passed through water breaks it into hydrogen and oxygen.
- Is this a chemical change or a physical change?
- Recall Grade 7, chapter 'Changes Around Us: Physical and Chemical'.
Important Points
- Pure substances are of two types: elements and compounds.
- Passing electricity splits water into hydrogen and oxygen.
- These gases are not water vapour — they would condense if they were.
Important Definitions
- Constituents — the simpler substances that make up a substance, like hydrogen and oxygen in water.
