GCSE CHEM: Can someone explain electrolysis in simple words please?Watch
- What happens in electrolysis
- The type of substances that can be electrolysed
- The products of electrolysis.
- Electrolysis means ‘breaking down using electricity’. Electric current is used to break down an ionic compound in electrolysis. The ionic compound which is broken down in Electrolysis is called the electrolyte.
- To set up an electric circuit for electrolysis, we have two electrodes that dip into the electrolyte, with a gap between them.
- The electrodes are conducting rods.In the electrolyte, the two conducting rods are dipped with the gap in between them known as electrode. The electrodes are connected to a battery.
- In electrolysis, the positive electrode is called the anodewhich is connected to a positive electrode where anions (negatively charged ions) move.
- The other one negative electrode is called thecathode which is connected to a negative electrode where cations (positively charged ions) move.
During electrolysis, positive charged ions move to the cathode. At the same time, the negative ions move to the anode, as opposite charges attract.
Below figure shows how electricity breaks down zinc chloride into zinc and chlorine:
Zinc chloride → zinc + chlorine
ZnCl2 (l) → Zn (s/l) + Cl2 (g)
- Zinc chloride is an ionic compound. We know that ionic compounds do not conduct electricity when they are solid, as their ions are in fixed positions in their giant lattice.
- However, once an ionic compound is melted, the ions are free to move around within the hot liquid and carry their charge towards the electrodes.
- The positive zinc ions, Zn2+,move towards the cathode (negative electrode). At the same time, the negative charged chloride ions, Cl–, move towards the anode (positive electrode).
Electrolysis of solutions:
- Many ionic substances have very high melting points which takes a lot of energy to melt them and free the ions to move to electrodes in electrolysis. However, some ionic substances dissolve in water and when this happens, the ions also become free to move around.
- In electrolysis only metal of very low reactivity, below hydrogen in the reactivity series are deposited from their aqueous solutions.
- For example, when we electrolyse an aqueous solution of copper (ll) bromide, copper ions, Cu2+, move to the cathode and the bromide ions, Br–, move to the anode. Copper (ll) bromide is split into its elements at the electrodes shown in the figure below:
Copper (ll) bromide → copper + bromide
CuBr2 (l) → Cu (s) + Br2 (aq)
The state symbols in the given equation shows that the copper bromide is dissolved in water and the copper formed is solid and the bromine formed dissolves in the water.
Electrolysis of Covalent Compounds
Covalent Compounds cannot be electrolysed unless they ionize in water when they are dissolved in water . For example acids dissolve in water to form H+ ions and negatively charged aqueous ions.
- Electrolysis breaks down a substance using electricity.
- Ionic compounds can only be electrolysed when they are molten or dissolved in water. This is because their ions are then free to move and carry their charge to the electrodes.
- In electrolysis, positive ions move to the cathode (negative electrode), while negative ions move to the anode (positive electrode).