Electrolysis Basics Quiz

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Questions and Answers

What is the direction of electron flow during electrolysis in the external circuit?

Randomly between the terminals

From positive to negative terminal (correct)

In a circular motion between terminals

From negative to positive terminal

Which terminal of the battery do electrons flow towards during electrolysis?

Positive terminal

Neutral terminal

Ground terminal

Negative terminal (correct)

Which of the following is a cation involved in electrolysis?

O2-

Cl-

Na+ (correct)

OH-

What is the role of the positive terminal in the electrolysis process?

It attracts electrons (B) Signup and view all the answers

Which of the following represents an anion in the electrolysis process?

Cl- (D) Signup and view all the answers

What happens to cations during electrolysis?

They receive electrons at the cathode (A) Signup and view all the answers

Where does reduction occur during electrolysis?

At the cathode (C) Signup and view all the answers

What is the role of ions in an electrolyte during electrolysis?

They carry electric current through the electrolyte (D) Signup and view all the answers

What charge do cations have?

Positive charge (A) Signup and view all the answers

During electrolysis, which component is associated with the flow of electrons?

Cations receiving electrons at the cathode (B) Signup and view all the answers

Which statement about electrolysis is true?

Cations move to the cathode during electrolysis (D) Signup and view all the answers

What is the result of cations receiving electrons at the cathode?

Reduction of the cations (D) Signup and view all the answers

Which of the following best describes the flow of electric current during electrolysis?

It is constituted by the movement of ions towards the electrodes (B) Signup and view all the answers

What happens to the anode during the purification of impure copper?

It decreases in mass. (B) Signup and view all the answers

In the electroplating process, what is the role of the cathode?

It is where the electroplating occurs. (A) Signup and view all the answers

What type of solution is used as an electrolyte in the purification of copper?

An aqueous solution of copper ions. (B) Signup and view all the answers

What occurs at the cathode during electroplating?

The object gains mass from deposited metal. (C) Signup and view all the answers

What is the source of the plating metal in electroplating?

The anode, which contains the plating metal. (C) Signup and view all the answers

What happens to anions at the anode during electrolysis?

They give up electrons. (D) Signup and view all the answers

What is the charge of the cathode in electrolysis?

Negatively charged (B) Signup and view all the answers

What occurs during the discharge of cations at the cathode?

They gain electrons. (C) Signup and view all the answers

Which process occurs at the anode during electrolysis?

Oxidation (A) Signup and view all the answers

Why can ionic compounds conduct electricity only in molten state or aqueous solution?

Ions are mobile in these states. (A) Signup and view all the answers

What happens to the flow of electric current in the electrolyte during electrolysis?

It flows from the anode to the cathode. (D) Signup and view all the answers

What are formed when cations and anions gain or lose electrons at the electrodes?

Atoms or molecules (C) Signup and view all the answers

What happens to solid NaCl during electrolysis?

No current flows through it. (D) Signup and view all the answers

What ions are present in molten copper (II) bromide?

Cu$^{2+}$ and Br$^{-}$ (C) Signup and view all the answers

During the electrolysis of molten copper (II) bromide, what is produced at the cathode?

Copper (D) Signup and view all the answers

Which ions are preferentially discharged in an aqueous sodium chloride solution?

H$^{+}$ and Cl$^{-}$ (A) Signup and view all the answers

What effect does the reactivity series have on the selective discharge of cations during electrolysis?

Less reactive metals are discharged preferentially (C) Signup and view all the answers

During the electrolysis of water, which ions compete with OH$^{-}$ for discharge?

H$^{+}$ and Na$^{+}$ (A) Signup and view all the answers

What ions are present in a dilute NaCl solution during electrolysis?

Na+, Cl-, H+, and OH- (C) Signup and view all the answers

Which anion is discharged at the anode during electrolysis of a dilute NaCl solution?

OH- (A) Signup and view all the answers

At which electrode does oxidation occur during the electrolysis of copper(II) bromide?

Anode (C) Signup and view all the answers

Which cation is preferentially discharged at the cathode during the electrolysis of dilute NaCl?

H+ (B) Signup and view all the answers

What is the main factor that determines which anion is discharged during electrolysis?

The concentration of the anion (B) Signup and view all the answers

Which ions are produced at the anode during electrolysis of sodium sulfate solution?

O$_2$ and H$^{+}$ (A) Signup and view all the answers

What is the overall chemical reaction at the cathode when H+ and OH- are discharged?

2H+ + 2e- → H2(g) (C) Signup and view all the answers

Which factor influences whether OH- or Cl- ions are discharged at the anode?

Concentration of the electrolyte (B) Signup and view all the answers

What is formed when OH- ions are discharged during electrolysis?

Oxygen gas (D) Signup and view all the answers

After electrolysis, what do the remaining cations and anions form?

Products in the solution (D) Signup and view all the answers

During electrolysis, which ions are attracted to the cathode?

H+ and Na+ (C) Signup and view all the answers

Study Notes

Electrolysis

Electrolysis is the process of using electricity to break down or decompose a compound, typically an ionic compound in molten or aqueous solution.
Electrolysis occurs in an electrolytic cell.

Learning Objectives

Define electrolysis.
Describe electrolysis as evidence of the structure of ionic compounds in the solid, molten, and aqueous states.
Predict the products of the electrolysis of a molten ionic compound.
Predict the products of the electrolysis of an aqueous electrolyte using the idea of selective discharge of ions.
Explain the reactivity series.
Construct ionic equations for the reactions occurring at the electrodes during electrolysis.

Parts of an Electrolytic Cell

Battery: Acts as an electron pump, drawing electrons from the anode and supplying them to the cathode. The anode becomes positively charged and the cathode negatively charged.
Electrodes: Conduct electricity. Usually carbon rods or metal plates. The electrode connected to the positive terminal is the anode, and the electrode connected to the negative terminal is the cathode.
Electrolyte: Conducts electricity. A molten ionic compound or an aqueous solution. Is decomposed to form positive ions (cations) and negative ions (anions).

How Does Electrolysis Work?

At the anode:
- Anions move to the anode.
- Anions give up electrons at the anode.
- Oxidation occurs at the anode.
At the cathode:
- Cations move to the cathode.
- Cations receive electrons at the cathode.
- Reduction occurs at the cathode.
Within the electrolyte:
- During electrolysis, the flow of ions towards the electrodes constitutes the flow of electric current through the electrolyte.
In the external circuit:
- During electrolysis, electrons flow from the negative terminal to the positive terminal of the battery.

What Happens to Ions at the Electrodes?

Cations receive electrons at the negatively-charged cathode.
Anions give up electrons at the positively-charged anode.
When cations/anions gain/lose electrons at the electrodes, they form atoms or molecules; this is called discharge.

Electrolysis as Evidence of the Structure of Ionic Compounds

Molten: Ionic compounds conduct electricity when liquefied by heat.
Solid: When solid NaCl is used, no current flows, indicating that ions are held in place in the lattice structure and cannot conduct electricity.

Electrolysis of Molten Ionic Compounds

A metal and a non-metal are formed as products.
The molten compound contains no water molecules.
At the anode (Example: NaCl): Negatively charged Cl ions are attracted to the anode and lose electrons to form chlorine gas. Oxidation occurs.
At the cathode (Example: NaCl): Positively charged Na ions are attracted to the cathode, gain electrons to form sodium metal. Reduction occurs.

Inert Electrodes

Inert electrodes (e.g., carbon, platinum) are used to prevent the produced chlorine (in molten NaCl electrolysis) from reacting with the electrode itself.
They do not react with the products or with the electrolyte.

Electrolysis of Aqueous Solutions

An aqueous solution of a compound is a mixture of the compound with water.
More than one type of cation or anion are present in the electrolyte.
Only one cation and one anion are preferentially discharged during electrolysis, known as selective discharge of ions.

Selective Discharge of Ions

Selective discharge depends on three factors:
- Selective discharge of cations (influenced by reactivity series).
- Selective discharge of anions (influenced by ease of discharge, concentration).
The more reactive a metal, the greater its tendency to form ions; hence, ease of discharge of cations is affected by its position in the reactivity series (e.g., H+ ions).
OH- ions preferentially discharge forming water and oxygen gas in most cases, unless concentration of other anions (like Cl-) is greater.

Predicting the Products of Electrolysis

Identify the cations and anions in the electrolyte.
Determine the anion that is discharged.
Determine the cation that is discharged.
Identify the remaining ions in solution after electrolysis.

Electrolysis of Dilute NaCl Solution

At the cathode: H+ ions are preferentially discharged forming hydrogen gas.
At the anode: OH- ions are preferentially discharged forming oxygen gas and water.

Electrolysis of Concentrated NaCl Solution

At the cathode: H+ ions are preferentially discharged forming hydrogen gas.
At the anode: Cl⁻ ions are preferentially discharged forming chlorine gas.

Electrolysis of CuSO4 Solution (Inert Electrodes)

At the anode: OH⁻ ions are preferentially discharged forming oxygen gas and water.
At the cathode: Cu²⁺ ions are preferentially discharged forming copper metal.

Electrolysis of CuSO4 Solution (Copper Electrodes)

At the anode, copper is oxidized, entering the solution as Cu²⁺.
At the cathode, Cu²⁺ gains electrons getting reduced to metallic copper.
The anode decreases in mass, whereas the cathode increases in mass.

Purification of Impure Copper

The impure copper is used as the anode, and a thin sheet of pure copper is used as the cathode.
The electrolyte is an aqueous solution of copper(II) sulfate.

Electroplating

The object to be plated is the cathode.
The anode is the source of the plating metal.
The electrolyte is an aqueous solution of a salt of the plating metal.

Questions (Examples)

Students are asked questions about different electrolysis scenarios (e.g., molten lead(II) bromide, molten copper(II) bromide, dilute/concentrated NaCl, etc...)

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Description

Test your knowledge on the fundamentals of electrolysis. This quiz covers topics such as electron flow, battery terminals, and the roles of cations and anions in the electrolysis process. Perfect for students looking to solidify their understanding of electrochemical reactions.