Splitting brine
Electricity turns salt water into three useful chemicals.
Zap the salt water
Brine is salt water: sodium chloride dissolved in water. Pass electricity through it.
What happens to the brine?
What this lesson covers
The idea
Passing electricity through brine (aqueous sodium chloride) decomposes it, giving chlorine gas at the anode, hydrogen gas at the cathode and sodium hydroxide solution near the cathode.
Zap the salt water
Brine is salt water: sodium chloride dissolved in water. Pass electricity through it.
What happens to the brine?
- It breaks up and new substances form
- Nothing, salt water is only salt and water
- It turns into pure salt crystals
Switch on the current
Press Switch on. Then find the three products.
The chlor-alkali process
When electricity is passed through brine (aqueous sodium chloride), it decomposes. Chlorine gas forms at the anode, hydrogen gas at the cathode, and sodium hydroxide solution forms near the cathode. This is the chlor-alkali process.
Chlor is for chlorine and alkali is for sodium hydroxide: the two names in the process.
- Where | What forms
- Anode (+) | chlorine gas, Cl₂
- Cathode (−) | hydrogen gas, H₂
- Near the cathode | sodium hydroxide solution, NaOH
Notes
Passing electricity through brine (aqueous sodium chloride) decomposes it, giving chlorine gas at the anode, hydrogen gas at the cathode and sodium hydroxide solution near the cathode.
Check yourself
Which gas is given off at the anode?
Which gas is given off at the cathode?
What is formed near the cathode?
Why is it called the chlor-alkali process?
- Hydrogen. Hydrogen is given off at the cathode.
- Chlorine — correct. Yes! Cl₂ at the anode.
- Oxygen. Not in this process. The gases are chlorine and hydrogen.
- Chlorine. Chlorine is given off at the anode.
- Carbon dioxide. Not in this process. The gases are chlorine and hydrogen.
- Hydrogen — correct. Yes! H₂ at the cathode.
- Sodium hydroxide solution — correct. Yes! NaOH, an alkali.
- Hydrochloric acid. The product near the cathode is an alkali, not an acid.
- Sodium chloride crystals. Sodium chloride is what we started with.
- It makes chlorine and an acid. The other product is an alkali, sodium hydroxide.
- It makes chlorine and an alkali (NaOH) — correct. Yes!
- It uses chlorine and alkali as starting materials. They are the products, not the starting materials.