C6 - Electrolysis Flashcards
(28 cards)
Describe how ionic compounds can conduct electricity when dissolved in water
- When ionic compound is melted or dissolved in water, the ions are free to move about within liquid or solution
- These liquids able to conduct electricity are called electrolyted
What is the process of electrolysis? Give the 4 key points.
- Electric current passed through electrolytes causing ions to move to electrodes
- Ions are discharged at the electrodes producing elements
- Positively charged ions move to the cathode(negative)
- Negatively charged ions move to the anode(positive)
What is produced at each electrode in a simple ionic compound?
- Electrolysed in molten state
- METAL produced at CATHODE
- NON-METAL produced at ANODE
What happens at the cathode in a simple molten ionic compound?
- Positively charged ions gain electrons to become metal atoms
- REDUCTION
What happens at the anode in a simple molten ionic compound?
- Negatively charged ions lose electrons
- OXIDATION
When is electrolysis used?
- If metal is too reactive to be extracted by reduction with carbon
What is an issue with electrolysis?
Large amounts of energy used in the extraction process to melt compounds and produce electrical current
Describe the extraction of aluminium
- Aluminium is manufactured by electrolysis of molten mixture of aluminium oxide and cryolite
What happens at the cathode(negative electrode) in terms of ions ?
- Aliminium(positive) ions move to cathode and form aluminium atoms by gaining 3 electrons
- REDUCTION
What happens at the anode(positive electrode) in terms of ions?
- Oxygen(negative) ions move to anode to react with carbon electrode and make CO2 by losing 2 electrons
- OXIDATION
Why must the positive electrode be continually replaced?
Because oxygen reacts with the carbon in the electrode to produce the CO2, burning it away
Why is a mixture used as the electrolyte?
- The mixture has a lower melting point than pure aluminium oxide
Why is cryolite used?
- Lowers the melting point of aluminum oxide
- Less amount of energy required
What does the ion discharged at the electrode depend on in an aq solution?
Relative reactivity of the elements involved
What happens at the cathode(negative)in an aq solution?
- Metal MORE reactive than hydrogen = hydrogen produced
What happens at the anode(positive) in an aq solution?
- Non-metal has oxygen = oxygen produced
- Non-metal is a halogen = halogen gas produced
Why do these changes happen in aq solutions?
- Water molecules break down producing hydrogen ions + hydroxide ions
RP3 - Electrolysis - investigate what happens when aq solutions are electrolysed using inert electrodes (7 STEPS)
- Add 50cm3 of copper chloride solution to beaker
- Add the lid and insert electrodes through the holes
- Attach crocodile leads to the electrode and connect the rods to the DC terminals of a low
voltage power supply - Switch power supply on
- Hold litmus paper near positive electrode
- After a few minutes, turn power supply off and observe negative electrode
- Record observations
RP3 - What would you observe with Copper Chloride at anode?
ANODE
- Bubbles of gas, Bleached litmus paper
- Chlorine gas formed
RP3 - What would you observe with Copper chloride at cathode?
CATHODE
- Pink/red coating on rod
- Copper formed
- Solid
RP3 - What would you observe with Sodium chloride at anode?
ANODE
- Bubbles of gas, Bleached litmus paper
- Chlorine gas formed
RP3 - What would you observe with Sodium chloride at cathode?
CATHODE
- Bubbles of gas(rapid production) - squeaky pop
- Hydrogen gas formed
RP3 - What would you observe with Copper sulphate at anode?
ANODE
- Bubbles, re-light glowing splint
- Oxygen gas produced
RP3 - What would you observe with Copper sulphate at cathode?
CATHODE
- Pink/red coating on rod
- Copper formed
- Solid
