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Electrolytic Cell

 
1.4 Electrolytic Cell
 
Definition of Electrolyte
Substances that can conduct electricity in either the molten state or aqueous solution and undergo chemical changes.
 
Definition of Non-Electrolytes
Substances that cannot conduct electricity in all states.
 
Classification of Substances into Electrolytes and Non-Electrolytes
This is a flowchart that categorizes substances into electrolytes and non-electrolytes. - **Substances** are divided into: - **Electrolyte** - **Ionic compound** - **Solid**: Cannot conduct electricity, ions in lattice structure cannot move freely. - **Molten or aqueous solution**: Can conduct electricity, presence of freely moving ions. - **Acids and alkalis** - **Absence of water**: Cannot conduct electricity, absence of freely moving ions. - **Presence of water**: Can conduct electricity, acids and alkalis ionize in water, presence of freely moving ions. - **Non-Electrolyte** - **
 
Apparatus Set Up for Electrolysis
This image depicts an electrochemical cell setup. It includes a battery connected to a galvanometer, which is labeled ‘G’. Two copper electrodes, labeled ‘X’ and ‘Y’, are submerged in a solution of copper (II) nitrate. The electrodes are connected to the battery and galvanometer with wires. The entire setup is shown on a blue background with a grid pattern.
 

 

 
Ion Discharged at Cation and Anion in An Electrolysis
The image is an infographic titled ‘Cation.’ It consists of four blue, vertically aligned oval shapes connected sequentially with red labels. The steps are as follows: 1. Cathode (negatively charged) 2. Reduction 3. Receives electrons 4. Decrease of oxidation number Each step is numbered from 01 to 04 and contains a brief description. The Pandai logo is at the bottom center of the image.
 

 

 

 

This image is a flowchart explaining the process related to anions. It consists of four blue, rounded rectangles arranged in a horizontal sequence. Each rectangle contains white text and is numbered from 01 to 04 with red labels at the top. The steps are as follows: 1. Anode (positively-charged) 2. Oxidation 3. Release of electrons 4. Increase of oxidation number At the bottom center, the logo and name ‘Pandai’ are displayed.
 
Comparison between Conductor and Electrolytes

Conductor

Electrolyte
  • Substances that conduct electricity in a solid or molten state, but do not undergo chemical changes.
  • Substances that conduct electricity in molten state or aqueous solution, and undergo chemical changes.
  • Substances that conduct electricity without undergoing decomposition.
  • Substances that conduct electricity and undergo decomposition into their constituent elements.
  • Can conduct electricity due to the presence of free moving electrons.
  • Can conduct electricity due to the presence of free moving ions.
  • Electrical conductivity decreases as temperature increases.
  • Electrical conductivity increases as temperature increases.
  • Examples of conductors are metals and graphite.
  • Examples of electrolytes are ionic compounds, acids and alkalis.
 
Electrolysis of Molten Compounds
Definition of Electrolysis
  • A process whereby compounds in the molten state or an aqueous solution decompose into their constituent elements by passing electricity through them.
Apparatus Set Up for Electrolysis of Molten Lead(II) Bromide

The image shows an electrolysis setup. It includes a battery connected to an ammeter and two carbon electrodes submerged in a container of molten lead (II) bromide. The battery provides the electrical energy needed for the process, and the ammeter measures the current flow. The carbon electrodes are the conductors through which the electric current enters and exits the molten lead (II) bromide.
Electrolysis of Molten Lead(II) Bromide

 

Ion Present \(Pb^{2+},\, Br^-\)
Terminal Anode Cathode
Ions Move to the Terminal \(Br^-\) \(Pb^{2+}\)
Hal Equation \(2Br^- \rightarrow Br_2 + 2e^-\) \(Pb^{2+} + 2e^- \rightarrow Pb\)
Observation Brown gas released Grey solid deposited
Name of Product Bromine gas Solid lead
Type of Reaction Oxidation Reduction
 
Factors that Affect the Electrolysis of An Aqueous Solution
  • The Eº value mentioned in the table is the Eº value in the standard electrode potential series. 
Factors Affecting the Electrolysis of An Aqueous Solution
E° value
Concentration of solution
Type of electrode

 
E° Value

 

Electrode Ion Chosen to be Discharged
Anode Anion with a more negative or less positive E° value will be easier to be discharged and oxidised.
Ctahode Cation with a more positive or less negative E° value will be easier to be discharged and reduced. 

 
Concentration of Solution

 

Electrode Ion Chosen to be Discharged
Anode
  • This factor is only considered for the selection of ions at the anode if the aqueous solution contains halide ions.
  • Halide ions with a higher concentration in the electrolytes will be discharged at the anode, even though the E° value of the halide ions are more positive.
Cathode Cation with a more positive or less negative E° value will be easier to be discharged.

 
Type of Electrode

 

Electrode Ion Chosen to be Discharged
Anode
  • For active electrodes (e.g. copper and silver).
  • No anions are discharged.
  • Metal atoms at the anode releases electrons to form metal ions.
Cathode Cation with a more positive or less negative E° value will be easier to be discharged.

 
 
Comparison between An Electrolytic Cell and Chemical Cell
Category Electrolytic Cell Chemical Cell
Electric sources Electrodes are connected to a battery or any electrical source. Electrodes are not connected to any electrical sources.
Electrolyte Both electrodes are dipped in the electrolyte.
Type of metal for electrodes Usually carbon electrodes. Different metals if being dipped in the same electrolyte.
The same metal if being dipped in a different electrolyte.
Negatively charged electrode Cathode. Positive terminal (less electropositive metal).
Positively charged electrode Anode. Negative terminal (more electropositive metal).
Energy conversion Electric energy → chemical energy. Chemical energy → electric energy.
Electron transfer Anion releases electrons at the anode. The atom at the negative terminal releases electrons.
Cation receives electrons at the cathode. Ions in the electrolyte receive electrons.
Oxidation At anode. At the negative terminal.
Reduction At cathode. At the positive terminal.
 
Electroplating of Metals
  • Electroplating of metals through electrolysis is done by making the object being electroplated as the cathode, the electroplating metal as the anode, and an aqueous solution containing the ions of the electroplating metal as the electrolyte.
  • For example, to electroplate an iron ring with copper, Cu, the copper anode ionises to become copper(II) ions, \(Cu^{2+}\).
    • Anode: \(Cu(s) \rightarrow Cu^{2+}(aq) + 2e^-\)
  • Copper(II) ions, \(Cu^{2+}\) move to the cathode, are discharged and deposited as a thin layer of copper, Cu on the iron ring.
    • Cathode: \(Cu^{2+}(aq) + 2e^- \rightarrow Cu(s) \)
  • The blue colour of copper(II) sulphate, \(CuSO_4\) solution does not change because the concentration of copper(II) ions, \(Cu^{2+}\) remains the same.
  • The rate of ionisation of copper, Cu at the anode is the same as the rate of discharged copper(II) ions, \(Cu^{2+}\) at the cathode.
 
Purification of Metals
  • Copper is an important mineral and element in our daily life.
  • It is an important industrial metal due to its ductility, malleability, electrical conductivity and resistance towards corrosion. 
  • Copper used in electrical wiring must have a 99.99% purity.
  • The purity of copper extracted by the process of melting is about 99.5%. 
  • Even a slight difference in copper purity will negatively impact its conductivity.
  • To determine whether a copper metal is pure, one must conduct the purification of metals through electrolysis.
  • The purification of copper by electrolysis is carried out with a piece of pure, thin copper as the cathode; impure copper as the anode; and an aqueous salt solution of copper, such as copper(II) nitrate, \(Cu(NO_3)_2\) as electrolyte.
  • Impure copper anode ionises to form copper(II) ions, \(Cu^{2+}\).
    • \(Cu(s) \rightarrow Cu^{2+}(aq) + 2e^-\)
  • Copper dissolves to become copper(II) ions, \(Cu^{2+}\) and impurities accumulate below the impure copper anode.
  • The anode becomes thinner.
  • At the pure copper cathode, copper(II) ions, \(Cu^{2+}\) are discharged to form copper atoms, Cu.
    • \(Cu^{2+}(aq) + 2e^- \rightarrow Cu(s) \)
  • Solid copper is deposited and the copper cathode becomes thicker.
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The views expressed in the notes here are those of the contributor and don’t necessarily represent the views of Pandai.

Electrolytic Cell

 
1.4 Electrolytic Cell
 
Definition of Electrolyte
Substances that can conduct electricity in either the molten state or aqueous solution and undergo chemical changes.
 
Definition of Non-Electrolytes
Substances that cannot conduct electricity in all states.
 
Classification of Substances into Electrolytes and Non-Electrolytes
This is a flowchart that categorizes substances into electrolytes and non-electrolytes. - **Substances** are divided into: - **Electrolyte** - **Ionic compound** - **Solid**: Cannot conduct electricity, ions in lattice structure cannot move freely. - **Molten or aqueous solution**: Can conduct electricity, presence of freely moving ions. - **Acids and alkalis** - **Absence of water**: Cannot conduct electricity, absence of freely moving ions. - **Presence of water**: Can conduct electricity, acids and alkalis ionize in water, presence of freely moving ions. - **Non-Electrolyte** - **
 
Apparatus Set Up for Electrolysis
This image depicts an electrochemical cell setup. It includes a battery connected to a galvanometer, which is labeled ‘G’. Two copper electrodes, labeled ‘X’ and ‘Y’, are submerged in a solution of copper (II) nitrate. The electrodes are connected to the battery and galvanometer with wires. The entire setup is shown on a blue background with a grid pattern.
 

 

 
Ion Discharged at Cation and Anion in An Electrolysis
The image is an infographic titled ‘Cation.’ It consists of four blue, vertically aligned oval shapes connected sequentially with red labels. The steps are as follows: 1. Cathode (negatively charged) 2. Reduction 3. Receives electrons 4. Decrease of oxidation number Each step is numbered from 01 to 04 and contains a brief description. The Pandai logo is at the bottom center of the image.
 

 

 

 

This image is a flowchart explaining the process related to anions. It consists of four blue, rounded rectangles arranged in a horizontal sequence. Each rectangle contains white text and is numbered from 01 to 04 with red labels at the top. The steps are as follows: 1. Anode (positively-charged) 2. Oxidation 3. Release of electrons 4. Increase of oxidation number At the bottom center, the logo and name ‘Pandai’ are displayed.
 
Comparison between Conductor and Electrolytes

Conductor

Electrolyte
  • Substances that conduct electricity in a solid or molten state, but do not undergo chemical changes.
  • Substances that conduct electricity in molten state or aqueous solution, and undergo chemical changes.
  • Substances that conduct electricity without undergoing decomposition.
  • Substances that conduct electricity and undergo decomposition into their constituent elements.
  • Can conduct electricity due to the presence of free moving electrons.
  • Can conduct electricity due to the presence of free moving ions.
  • Electrical conductivity decreases as temperature increases.
  • Electrical conductivity increases as temperature increases.
  • Examples of conductors are metals and graphite.
  • Examples of electrolytes are ionic compounds, acids and alkalis.
 
Electrolysis of Molten Compounds
Definition of Electrolysis
  • A process whereby compounds in the molten state or an aqueous solution decompose into their constituent elements by passing electricity through them.
Apparatus Set Up for Electrolysis of Molten Lead(II) Bromide

The image shows an electrolysis setup. It includes a battery connected to an ammeter and two carbon electrodes submerged in a container of molten lead (II) bromide. The battery provides the electrical energy needed for the process, and the ammeter measures the current flow. The carbon electrodes are the conductors through which the electric current enters and exits the molten lead (II) bromide.
Electrolysis of Molten Lead(II) Bromide

 

Ion Present \(Pb^{2+},\, Br^-\)
Terminal Anode Cathode
Ions Move to the Terminal \(Br^-\) \(Pb^{2+}\)
Hal Equation \(2Br^- \rightarrow Br_2 + 2e^-\) \(Pb^{2+} + 2e^- \rightarrow Pb\)
Observation Brown gas released Grey solid deposited
Name of Product Bromine gas Solid lead
Type of Reaction Oxidation Reduction
 
Factors that Affect the Electrolysis of An Aqueous Solution
  • The Eº value mentioned in the table is the Eº value in the standard electrode potential series. 
Factors Affecting the Electrolysis of An Aqueous Solution
E° value
Concentration of solution
Type of electrode

 
E° Value

 

Electrode Ion Chosen to be Discharged
Anode Anion with a more negative or less positive E° value will be easier to be discharged and oxidised.
Ctahode Cation with a more positive or less negative E° value will be easier to be discharged and reduced. 

 
Concentration of Solution

 

Electrode Ion Chosen to be Discharged
Anode
  • This factor is only considered for the selection of ions at the anode if the aqueous solution contains halide ions.
  • Halide ions with a higher concentration in the electrolytes will be discharged at the anode, even though the E° value of the halide ions are more positive.
Cathode Cation with a more positive or less negative E° value will be easier to be discharged.

 
Type of Electrode

 

Electrode Ion Chosen to be Discharged
Anode
  • For active electrodes (e.g. copper and silver).
  • No anions are discharged.
  • Metal atoms at the anode releases electrons to form metal ions.
Cathode Cation with a more positive or less negative E° value will be easier to be discharged.

 
 
Comparison between An Electrolytic Cell and Chemical Cell
Category Electrolytic Cell Chemical Cell
Electric sources Electrodes are connected to a battery or any electrical source. Electrodes are not connected to any electrical sources.
Electrolyte Both electrodes are dipped in the electrolyte.
Type of metal for electrodes Usually carbon electrodes. Different metals if being dipped in the same electrolyte.
The same metal if being dipped in a different electrolyte.
Negatively charged electrode Cathode. Positive terminal (less electropositive metal).
Positively charged electrode Anode. Negative terminal (more electropositive metal).
Energy conversion Electric energy → chemical energy. Chemical energy → electric energy.
Electron transfer Anion releases electrons at the anode. The atom at the negative terminal releases electrons.
Cation receives electrons at the cathode. Ions in the electrolyte receive electrons.
Oxidation At anode. At the negative terminal.
Reduction At cathode. At the positive terminal.
 
Electroplating of Metals
  • Electroplating of metals through electrolysis is done by making the object being electroplated as the cathode, the electroplating metal as the anode, and an aqueous solution containing the ions of the electroplating metal as the electrolyte.
  • For example, to electroplate an iron ring with copper, Cu, the copper anode ionises to become copper(II) ions, \(Cu^{2+}\).
    • Anode: \(Cu(s) \rightarrow Cu^{2+}(aq) + 2e^-\)
  • Copper(II) ions, \(Cu^{2+}\) move to the cathode, are discharged and deposited as a thin layer of copper, Cu on the iron ring.
    • Cathode: \(Cu^{2+}(aq) + 2e^- \rightarrow Cu(s) \)
  • The blue colour of copper(II) sulphate, \(CuSO_4\) solution does not change because the concentration of copper(II) ions, \(Cu^{2+}\) remains the same.
  • The rate of ionisation of copper, Cu at the anode is the same as the rate of discharged copper(II) ions, \(Cu^{2+}\) at the cathode.
 
Purification of Metals
  • Copper is an important mineral and element in our daily life.
  • It is an important industrial metal due to its ductility, malleability, electrical conductivity and resistance towards corrosion. 
  • Copper used in electrical wiring must have a 99.99% purity.
  • The purity of copper extracted by the process of melting is about 99.5%. 
  • Even a slight difference in copper purity will negatively impact its conductivity.
  • To determine whether a copper metal is pure, one must conduct the purification of metals through electrolysis.
  • The purification of copper by electrolysis is carried out with a piece of pure, thin copper as the cathode; impure copper as the anode; and an aqueous salt solution of copper, such as copper(II) nitrate, \(Cu(NO_3)_2\) as electrolyte.
  • Impure copper anode ionises to form copper(II) ions, \(Cu^{2+}\).
    • \(Cu(s) \rightarrow Cu^{2+}(aq) + 2e^-\)
  • Copper dissolves to become copper(II) ions, \(Cu^{2+}\) and impurities accumulate below the impure copper anode.
  • The anode becomes thinner.
  • At the pure copper cathode, copper(II) ions, \(Cu^{2+}\) are discharged to form copper atoms, Cu.
    • \(Cu^{2+}(aq) + 2e^- \rightarrow Cu(s) \)
  • Solid copper is deposited and the copper cathode becomes thicker.
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The views expressed in the notes here are those of the contributor and don’t necessarily represent the views of Pandai.
Chapter : Redox Equilibrium
Topic : Electrolytic Cell
Form 5 Chemistry
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