C4 - Electrolysis in Aqeaous Solutions pt2

What does aqueous mean?

Dissolved in water

What ions does water split into?

Hydrogen ions (H⁺) and hydroxide ions (OH⁻)

What are the ions present in sodium chloride solution?

Sodium ions (Na⁺) and chloride ions (Cl⁻)

What extra ions are present in any aqueous solution?

H⁺ and OH⁻ from water

What happens at the cathode (negative electrode)?

Positively charged ions gain electrons (reduction)

What happens at the anode (positive electrode)?

Negatively charged ions lose electrons (oxidation)

Which ions move to the cathode?

Positive ions (cations) like Na⁺ and H⁺

Which ions move to the anode?

Negative ions (anions) like Cl⁻ and OH⁻

How do you decide what is produced at the cathode?

Use the reactivity series: the less reactive ion is discharged

What is produced at the cathode if hydrogen is less reactive than the metal?

Hydrogen gas (H₂)

What is produced at the cathode in electrolysis of sodium chloride solution?

Hydrogen gas (H₂)

Why is hydrogen produced at the cathode in sodium chloride solution?

Sodium is more reactive than hydrogen

How do you decide what is produced at the anode?

If a halide ion is present, the halogen is discharged; otherwise oxygen is released

What is produced at the anode in electrolysis of sodium chloride solution?

Chlorine gas (Cl₂)

Why is chlorine produced at the anode in sodium chloride solution?

Because chloride is a halide ion

What are the four common halide ions?

Cl⁻ (chloride), Br⁻ (bromide), I⁻ (iodide), F⁻ (fluoride)

What is produced at the anode if no halide ions are present?

Oxygen gas (O₂)

What gas is produced at the anode if the solution contains sulfate or nitrate ions?

Oxygen gas (O₂)

What is the general rule for cathode products in aqueous electrolysis?

Hydrogen is produced if the metal is more reactive than hydrogen

What is the general rule for anode products in aqueous electrolysis?

A halogen is produced if halide ions are present; otherwise oxygen is produced

What is the half-equation at the cathode for hydrogen production?

2H⁺ + 2e⁻ → H₂

What type of reaction happens at the cathode?

Reduction (gain of electrons)

Why is the hydrogen half-equation doubled?

Because hydrogen atoms pair up to form H₂ molecules

What is the half-equation at the anode for chlorine production?

2Cl⁻ → Cl₂ + 2e⁻

What type of reaction happens at the anode?

Oxidation (loss of electrons)

Why is the chlorine half-equation doubled?

Because chlorine atoms pair to form Cl₂ molecules

What is oxidation in terms of electrons?

Loss of electrons

What is reduction in terms of electrons?

Gain of electrons

What is the mnemonic for remembering oxidation and reduction?

OIL RIG: Oxidation Is Loss, Reduction Is Gain (of electrons)

What is an electrolyte?

A liquid or solution that conducts electricity due to the presence of ions

What happens during electrolysis?

An electric current causes a chemical change by breaking down an electrolyte

Why must the electrodes be inert?

So they don't react with the products or the electrolyte

What is an example of an inert electrode?

Graphite or platinum

Why is electrolysis important?

It is used to extract reactive metals and produce useful gases

What is the role of the power supply in electrolysis?

To provide energy for the movement of electrons and ion discharge

What is meant by ion discharge in electrolysis?

When ions gain or lose electrons and become neutral atoms or molecules

What are spectator ions?

Ions that are present but do not take part in the electrolysis reaction

How do you identify the products of electrolysis in an unknown aqueous solution?

Use the rules for reactivity and halide presence to predict products at electrodes

What must higher-tier students be able to do for electrolysis of aqueous solutions?

Write balanced half-equations for reactions at the anode and cathode