Electric Chemistry
The same solution, electrolysed twice, with only the electrodes changed - and the blue colour behaves completely differently. Why that happens is the whole practical.
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Pulling a compound apart ⚡
Electrolysis uses electricity to split a compound into the elements it is made from. It only works if the **ions can move**, so the substance has to be melted or dissolved first. The core practical does something clever with that: it runs the **same** experiment twice on the **same** copper sulfate solution, changing only what the electrodes are made of. The results are strikingly different, and explaining why is what the question is actually about.
The words you need 🗂️
Get these right and the rest of the topic describes itself:
Match each term to what it means
- Electrolyte
- Cathode
- Anode
- Inert electrode
- the molten or dissolved substance with ions free to move
- the negative electrode, which attracts positive ions
- the positive electrode, which attracts negative ions
- one that carries current without taking part in the reaction
Same solution, different electrodes ⚖️
This is CP 3.31, and it is the contrast the practical exists to show. Copper sulfate solution both times; only the electrodes change.
Why does the colour behave differently? ❓
With graphite electrodes the blue colour fades, but with copper electrodes it stays the same. Why?
- With copper electrodes the copper ions removed at the cathode are replaced by copper dissolving at the anode
- The reaction happens faster with copper electrodes, so there is no time for the colour to change
- Graphite adds a dark colour that masks the blue
- The oxygen produced at the anode bleaches the solution
Order the practical 🪜
An interactive activity.
The total mass change 🔢
An interactive activity.
Electrons in and out [Higher tier only] 🎓
**This card and the three steps after it are Higher tier.** If you are sitting Foundation you do not need half equations - skip ahead without worrying. On Higher, oxidation and reduction are defined by **electrons**, not by oxygen: **OIL RIG** - **O**xidation **I**s **L**oss, **R**eduction **I**s **G**ain, of electrons. **At the cathode**, copper ions gain electrons: Cu2+ + 2e- becomes Cu. That is **reduction**. **At the anode of a copper-electrode cell**, copper atoms lose electrons: Cu becomes Cu2+ + 2e-. That is **oxidation**. **And that pair is the whole practical in symbols**: what dissolves at one electrode is exactly what is deposited at the other.
Build the half equations [Higher tier only] 📝
Higher tier. At the cathode a copper ion _____ two electrons and becomes a copper atom: Cu2+ + 2e- _____ Cu. Gaining electrons is called _____. At the anode of a copper-electrode cell the opposite happens: a copper atom _____ two electrons, which is called _____.
How many electrons? [Higher tier only] ➕
An interactive activity.
Which are correct? [Higher tier only] ✅
Higher tier. Select the TWO correct statements.
- Reduction happens at the cathode, because ions gain electrons there
- Oxidation happens at the anode, because atoms or ions lose electrons there
- Oxidation can only mean gaining oxygen
- Oxidation happens at the cathode
At the bench 🧭
An interactive activity.
Your turn ✍️
An interactive activity.