Chapter 4- Electrochemistry

What does the term electrolysis mean?

The breakdown of a molten or aqueous ionic compound using electricity.

What is the cathode and anode?

Cathode = negatively charged electrode. Anode = positively charged electrode.

What is an electrolyte?

An ionic compound in the molten or aqueous state that undergoes electrolysis.

What happens to ions in the electrolyte?

They move freely and are attracted to oppositely charged electrodes.

What is formed at each electrode in electrolysis?

Positive electrode (anode): non-metal. Negative electrode (cathode): metal or hydrogen.

How can you predict whether a metal or hydrogen forms at the cathode in aqueous electrolysis?

If the metal is less reactive than hydrogen, the metal forms. If more reactive, hydrogen forms.

What forms at each electrode during electrolysis of molten lead(II) bromide?

Anode: bromine. Cathode: lead.

What forms at each electrode during electrolysis of concentrated hydrochloric acid?

Anode: chlorine. Cathode: hydrogen.

What forms at each electrode during electrolysis of concentrated sodium chloride solution?

Anode: chlorine. Cathode: hydrogen.

What forms at each electrode during electrolysis of dilute sulfuric acid?

Anode: oxygen. Cathode: hydrogen.

How can the products of electrolysis of molten electrolytes be predicted?

Anode forms non-metal element. Cathode forms metal element.

Predict the products of electrolysis of molten zinc chloride.

Anode: chlorine. Cathode: zinc.

Predict the products of electrolysis of concentrated potassium bromide solution.

Positive electrode: bromine. Negative electrode: hydrogen.

Predict the products of electrolysis of concentrated copper iodide solution.

Positive electrode: iodine. Negative electrode: copper.

Predict the products of electrolysis of dilute zinc chloride solution.

Positive electrode: oxygen. Negative electrode: zinc.

What is electroplating?

Coating a metal with a layer of another metal.

Why is electroplating used?

To increase resistance to corrosion and improve appearance.

How does electroplating work?

The object being coated is the cathode, the coating metal is the anode, and the electrolyte contains ions of the coating metal.

Describe transfer of charge during electrolysis.

The power supply provides electrons to the cathode. Cations gain electrons at the cathode. Anions lose electrons at the anode. Electrons flow back through the circuit.

Compare movement of electrons and ions in electrolysis.

Electrons move through wires. Ions move through the electrolyte.

What forms at each electrode during electrolysis of copper sulfate using inert electrodes?

Anode: oxygen. Cathode: copper.

What forms at each electrode during electrolysis of copper sulfate using copper electrodes?

Positive electrode: copper ions. Negative electrode: copper.

Describe electrolysis of copper(II) sulfate using carbon electrodes.

Copper ions gain electrons at the cathode to form copper, while oxygen forms at the anode.

How can impure copper be purified?

Impure copper is the anode, pure copper is the cathode, copper ions move to the cathode, and impurities fall as sludge.

What forms at each electrode when an aqueous electrolyte contains a halide?

Anode forms halogen. Cathode forms the metal.

What does chloride ion form at the anode?

Chlorine gas.

What does bromide ion form at the anode?

Bromine.

What does iodide ion form at the anode?

Iodine.

What is oxidation?

Loss of electrons.

Where does oxidation occur?

At the anode.

Where does reduction occur?

At the cathode.

What does OILRIG stand for?

Oxidation Is Loss, Reduction Is Gain (of electrons).

What are the features of half-equations?

They show gain/loss of electrons, use e−, charges balance, and atoms balance.

Write the half equation for oxidation of bromide ions.

2Br⁻ → Br₂ + 2e⁻

Write the half equation for reduction of sodium ions.

Na⁺ + e⁻ → Na

Write the half equations for molten lead(II) bromide electrolysis.

Cathode: Pb²⁺ + 2e⁻ → Pb. Anode: 2Br⁻ → Br₂ + 2e⁻

What is a hydrogen-oxygen fuel cell?

A cell that uses hydrogen and oxygen to produce electricity with water as the only chemical product.

What is the word equation for a hydrogen-oxygen fuel cell?

Hydrogen + oxygen → water.

What is the symbol equation for a hydrogen-oxygen fuel cell?

2H₂ + O₂ → 2H₂O

Advantages of hydrogen-oxygen fuel cells?

Less CO₂ emissions, reduced fossil fuel use, hydrogen can come from renewable sources.

Disadvantages of hydrogen-oxygen fuel cells?

Expensive, difficult hydrogen storage, hydrogen production may release CO₂, less durable than petrol/diesel engines.