Upgrade to remove ads
Only $2.99/month

AQA 9-1 Chemistry -- Electrolysis

Terms in this set (20)

Electric current
- Used to break down an ionic compound
- The compound that is broken down is called the ELECTROLYTE
Electrodes
- Conducting rods that are usually made of inert substances so it does not react with the electrolyte
Where do charged ions move towards?
- Positive; the negative electrode (cathode)
- Negative; the positive electrode (anode)
What happens when the ions reach the electrodes?
- They LOSE their charge and become elements
What happens at the electrodes?
- Gases may be given off or metals deposited depeding on the compound used and whether it is molten or dissolved in water
Ionic substances
- Have high mps so LOTS of energy is needed to melt them and free the ions to move to electrodes
- Some DISSOLVE in water so the ions become free to move
Why is it difficult to predict what will be formed when electrolysing ionic compounds in solution?
- Water also forms ions
- Only metals of low reactivity are deposited from their aqueous solutions
Covalent compounds
- Usually CANNOT be electrolysed unless they react with WATER to form ions
Mobile ions
- Move towards the electrodes
- Direction depends on their CHARGE
- Once reached, they LOSE or GAIN electrons
Gaining and losing electrons
- Negatively charged ions LOSE electrons to become neutral atoms
- Positively charged ions GAIN electrons to become neutral atoms
Negative electrode
- Positive ions gain electrons, so are reduced
Positive electrode
- Negative ions lose their EXTRA electrons, so are oxidised
Electrolysis in an aqueous solution
- The less reactive e
element is usually produced at the CATHODE
- The ANODE usually produces O₂ gas or a halogen if the electrolyte is a solution of halide
Aluminium
- Cannot be displaced by carbon as it is not reactive enough
- Al. oxide comes from the ore bauxite but is mixed with other rocky impurities so has to be separated from the ore
- Requires LOTS of energy
Melting the al. oxide
- Happens once purified
- Enables ions to move to the electrodes
- High mp of 2050 so is mixed with molten cryolite (can be electrolysd at aroud 850)
- The large amount of electrical energy transferred to the electrolysis cells KEEPS the mixture molten
What is formed/produced at the anode and cathode?
- C; Aluminium is formed
- A; O₂ is produced
What dos the O₂ do?
- It reacts with the hot C anodes, making CO₂ gas
- The C anodes gradually BURN away and need to be replaced regularly
Electrolysis of brine products
- Chlorine gas at the aode
- Hydrogen gas at the cathode
- Sodium hydroxide solution
What is produced at the cathode?
- Hydrogen as H+ (aq) ions are DISCHARGED from the sol in prefece to Na+ (aq) ions
What is produced at the anode?
- Chlorine as Cl- (aq) ions are DISCHARGED from the sol in preface to OH+ (aq) ions
THIS SET IS OFTEN IN FOLDERS WITH...