What is electrolysis?
The splitting of a compound to its elements by passing electricity through it.
What are examples of good electrolytes?
- All ionic compounds
- Strong acids (HCl, HNO₃, H₂SO₄)
- Water
How does electrolysis work?
Electrodes attached to a DC electricity supply are place into the molten electrolyte/solution of the electrolyte. Cations from the electrolyte migrate towards the cathode and anions from the electrolyte migrate towards the anode.
What is oxidation and reduction?
Oxidation is the loss of electrons.
Reduction is the gain of electrons.
OIL RIG
What are the different types of reactions at the electrodes?
Anode: oxidation occurs
Cathode: reduction occurs
What is the order in the reactivity series?
Check camera roll and reactivity series handout.
What is the half-equation for hydroxide ions?
4OH⁻ - 4e⁻ –> 2H₂O + O₂
What is the required apparatus for electrolysis (copper sulfate)?
- Balance measuring to at least 1dp
- Use of propanone in a fume cupboard
- Copper sulfate solution
- 2 pieces of copper foil
- 2 graphite rods
- Stop clock
- Beaker
- Crocodile clips
- Wires
- Power pack
- Variable resistor
- Ammeter
- Sand paper
What is the method of performing electrolysis (copper sulfate)?
Method 1 - Copper electrodes:
1. Take 2 pieces of copper foil and clean them with sand paper
2. Measure and record the mass of each of the electrodes
3. Attach the pieces of copper foil to crocodile clips and wires
4. Connect the ammeter and variable resistor in series with wires and pieces of copper foil, making note of which is the anode and which is the cathode
5. Fill a beaker with 150cm³ of copper sulfate solution
6. Place the copper foil electrodes into the solution
7. Set the current to 0.2A using the variable resistor and leave for 20 minutes
8. Adjust the variable resistor if this current changes from 0.2A during this time
9. Turn off the power and wash the electrodes using distilled water
10. Record the mass of each of the electrodes and repeat the process using 0.3, 0.4 and 0.5A
11. As current increases, the mass of the anode decreases and the mass of the cathode should increase (increase and decrease should be equal)
Method 2 - Inert electrodes:
1. Using same equipment as method 1, change the copper electrodes so they are graphite electrodes
2. Adjust the current until you can observe changes at the anode and cathode and record what you can see
3. Small bubbles of gas should be seen at the anode and a brown deposit of copper should be seen coating the cathode
What are the independent and dependent variables in the electrolysis experiment (copper sulfate)?
- Concentration of copper sulfate solution
- Volume of copper sulfate
- Amount of electrode cleaning
What improvements could be made to the electrolysis experiment (copper sulfate)?
- Do not touch electrodes, this will cause sparks and electrolysis will not take place
- Ensure current stays constant using variable resistor
- Ensure electrodes are dry after dipping them in propanone to get an accurate mass
What are some safety precautions for the electrolysis experiment?
- Wear eye protection to protect against splashes from copper sulfate
- Use propanone in a well-ventilated area and away from naked flames
- Be aware of sharp edges on copper foil
What characteristics must the materials that are used for the electrodes have?
- Inert so products will not react with electrodes
- Good conductors of electricity
E.g. Graphite, platinum
How can copper be purified by electrolysis?
Copper can be purified by the electrolysis of copper sulfate solution using copper electrodes. The copper atoms in the anode lose electrons to become copper ions. These dissolve in the solution and migrate to the cathode, where they are deposited as pure copper. Impurities from the anode do not form ions and collect below the anode (‘sludge’).
What is electroplating?
Coating the surface of a metal with a thin layer of another metal.
How does electroplating work?
The cathode is the object to be plated and the anode is the pure metal.
What are different uses of electroplating?
- Silver/gold plating used to make jewellery that is cheaper than using the pure metal
- Electroplating metals that corrode easily (such as iron) with metals that are resistant to corrosion
