Split Water with Electricity
Observe hydrogen and oxygen production via electrolysis.
What this lesson covers
Why it matters
Pass electricity through acidulated water and watch it split into two invisible gases. One burns with a pop, the other relights a glowing splint.
The idea in plain words
Balance the split yourself: how many water molecules must break apart to free one whole O₂? Count each element — then check that your coefficients explain the two gas levels in the tubes.
Predict first
Which gas collects in a larger volume at the cathode?
Hydrogen collects in double the volume of oxygen because water contains two hydrogen atoms for every one oxygen atom.
- Oxygen
- Hydrogen — correct
- Equal volumes of both
What you do
Switch on the current. Observe the gas levels in the two 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.
Which gas collects at the anode (positive electrode), and how would you test it?
Oxygen forms at the positive anode — half the volume of the hydrogen at the cathode — and a glowing splint bursts back into flame in it.
Which gas is collected at the cathode (negative electrode)?
Hydrogen ions (H⁺) are positively charged and migrate to the negative cathode to gain electrons and form H₂ gas.
- 1:2
- 2:1 — correct
- 1:1
- 3:1
- Oxygen — it relights a glowing splint — correct
- Hydrogen — it pops with a burning splint
- Carbon dioxide — it turns lime water milky
- Oxygen
- Hydrogen — correct
- Water vapour