C3.4 Flashcards
What is electrolysis?
The breaking down of an ionic compound using electricity.
What is the mnemonic for oxidation and reduction?
OIL RIG — Oxidation Is Loss, Reduction Is Gain (of electrons).
What happens at the cathode during electrolysis?
Positive ions (cations) move to the cathode and gain electrons (reduction).
What happens at the anode during electrolysis?
Negative ions (anions) move to the anode and lose electrons (oxidation).
What type of substance can be electrolyzed?
Ionic compounds when they are molten or dissolved in water (aqueous).
What forms at the cathode in electrolysis of molten ionic compounds?
Metals or hydrogen (if present).
What forms at the anode in electrolysis of molten ionic compounds?
Non-metals, such as halogens or oxygen.
When is hydrogen produced at the cathode in aqueous solutions?
When the metal in the solution is more reactive than hydrogen.
In electrolysis of aqueous solutions, what ions are present besides the ionic compound?
H⁺ (hydrogen) and OH⁻ (hydroxide) ions from water.
When is oxygen produced at the anode in aqueous solutions?
When there are no halide ions present.
OH⁻ ions are discharged to form O₂ gas.
What forms at the anode if halide ions (Cl⁻, Br⁻, I⁻) are present?
The corresponding halogen is produced.
Chloride (Cl⁻) → Chlorine (Cl₂)
Bromide (Br⁻) → Bromine (Br₂)
Iodide (I⁻) → Iodine (I₂)
What are inert electrodes?
Electrodes that do not react during electrolysis, such as graphite or platinum.
Why are non-inert electrodes used in some electrolysis reactions?
To allow purification or plating reactions where the electrode itself takes part.
What is formed at the cathode in the electrolysis of sodium chloride (NaCl) solution?
Hydrogen gas (H₂) because sodium is more reactive than hydrogen.
What is formed at the anode in the electrolysis of sodium chloride (NaCl) solution?
Chlorine gas (Cl₂) because of the presence of halide ions (Cl⁻).
What forms at the anode in the electrolysis of copper sulfate (CuSO₄) solution?
Oxygen gas (O₂) because sulfate ions (SO₄²⁻) are not halides.
What forms at the cathode in the electrolysis of copper sulfate (CuSO₄) solution?
Copper metal (Cu) because it is less reactive than hydrogen.
What is the equation for the reaction at the cathode when hydrogen is produced?
2H⁺ + 2e⁻ → H₂
What is the equation for the reaction at the anode when oxygen is produced?
4OH⁻ → O₂ + 2H₂O + 4e⁻
What is the purpose of electroplating?
To coat the surface of a metal object with another metal for appearance or protection.
Why is electrolysis expensive?
It requires a lot of energy for electricity and to melt ionic compounds.
In the purification of copper, what is used as the anode and cathode?
Anode: Impure copper (loses Cu²⁺ ions).
Cathode: Pure copper (gains Cu²⁺ ions).
How do you identify the ions present in an electrolysis reaction?
Split the ionic compound into positive and negative ions.
Include H⁺ and OH⁻ if aqueous.
Positive ions → Cathode (Reduction)
Negative ions → Anode (Oxidation)
What is the difference between molten and aqueous electrolysis?
Molten: Only ionic compound ions present.
Aqueous: Ions from water (H⁺ and OH⁻) also present.
Why is cryolite used in the electrolysis of aluminium oxide?
It lowers the melting point of aluminium oxide, reducing energy costs.
