Splitting Water: H₂ and O₂
Electrolyze acidified water to produce hydrogen and oxygen.
Setting up the bench…
What this lesson covers
Why it matters
Pass electricity through water and watch it split into two invisible gases. The cathode collects twice as much gas as the anode.
The idea in plain words
Match the observation: 2 volumes of H₂ for every 1 volume of O₂.
Predict first
Which gas collects at the cathode (negative electrode)?
Hydrogen ions (H⁺) migrate to the negative cathode, gain electrons, and form hydrogen gas.
- Oxygen
- Hydrogen — correct
- Nitrogen
What you do
Turn on the current. Observe the gas volumes in both tubes over time.
Check yourself
What is the volume ratio of Hydrogen to Oxygen collected?
The equation 2H₂O → 2H₂ + O₂ shows 2 moles of H₂ for 1 mole of O₂, resulting in a 2:1 volume ratio.
Why is dilute acid added to the water?
Pure water is a poor conductor; acid provides ions to carry the current.
- 1:1
- 2:1 — correct
- 1:2
- To make the water conduct electricity — correct
- To produce more oxygen
- To cool the solution