Explaining Electrolysis (GCSE Chemistry)

Explaining Electrolysis

Electrolysis

Electrolytes

• Ionic compounds contain ions. When ionic compounds are melted or dissolved in water, the ions in the compound are free to move about in the liquid or solution. These ions can be positively charged or negatively charged.
• Ions are free to move around. The ions in a molten or aqueous ionic compound are free to move around. When ions move, they can conduct electricity, therefore creating a current.
• Electrolytes can conduct electricity. These molten and aqueous solutions are known as electrolytes. As we’ve just discussed, the electrolytes can conduct electricity.

The Process of Electrolysis

• Electrolysis splits up ionic compounds. By using direct electrical currents, we can split up ionic compounds into their positive and negative ions through the process of electrolysis. There are two electrodes, one positive and one negative. These will direct current through an electrolyte, which the substance being split.
• A current needs to pass through. In order to make to the electrolyte move, we must pass an electric current through it. This will cause the ions to move towards the electrodes.
• Electrodes are charged. When we perform electrolysis, we use two electrodes. One electrode is positively charged, which is called the anode. The other electrode is negatively charged, which is called the cathode.
• Electrolytes are attracted to the electrodes. Due to opposite charges attracting, any positive ions will move towards the cathode (since it is the negative electrode). Any negative ions will move towards the anode (since it is the positive electrode).
• Ions are reduced or oxidised. The positive ions will be reduced at the cathode, as they gain electrons. The negative ions will be oxidised at the anode, as they lose electrons.
• A flow of charge is created. The movement of ions through the electrolyte creates a flow of charge. Once the ions gain or lose electrons, they become uncharged. These uncharged elements then become discharged from the electrolyte.

Writing Half Equations

For exams, you need to be able to write half equations for the reactions occurring during electrolysis. Sometimes, you will be asked to write and balance half equations given in a question.

Practice Question: Write out the half equations for the electrolysis of lead (II) bromide.

1.Write out the balanced equation. In this instance, we need to write out a full balanced equation so we can identify the ions in our next step.

PbBr₂ → Pb + Br₂

2. Write out the half equation for the positive ion. In this instance, the positive ion is lead (as it is the metal ion).

Pb²⁺ + 2e^– → Pb

3. Write out the half equation for the negative ion. In this instance, the negative ion is bromide (as it is the non-metal).

2Br^– – 2e^– → Br₂