Electrolysis Principles and Conductivity
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Questions and Answers

What happens to the mass of the anode during the electrolysis of copper(II) sulfate?

  • It decreases (correct)
  • It remains the same
  • It increases
  • It fluctuates

    • The concentration of Cu2+ ions in the solution changes during the electrolysis process.

    False (B)

    What is the product formed at the cathode during the electrolysis of concentrated copper(II) sulfate solution?

    Copper

    What gas is produced at the anode when electrolysis occurs with dilute barium chloride solution?

    <p>Oxygen gas (D)</p> Signup and view all the answers

    During the electrolysis of dilute sodium chloride, the product at the anode is __________.

    <p>Oxygen gas</p> Signup and view all the answers

    In electrolysis, if a metal is above hydrogen in the reactivity series, hydrogen will be produced at the cathode.

    <p>True (A)</p> Signup and view all the answers

    Match the aqueous solutions with their respective products at the anode:

    <p>Concentrated sodium chloride, NaCl = Chlorine gas Dilute sodium chloride, NaCl = Oxygen gas Concentrated copper(II) sulfate, CuSO4 = Oxygen gas Dilute sulfuric acid, H2SO4 = Oxygen gas</p> Signup and view all the answers

    What is the role of the cathode in electrolysis?

    <p>It is the negative electrode where reduction occurs.</p> Signup and view all the answers

    If the metal is below hydrogen in the reactivity series, the ______ metal ions are discharged.

    <p>less reactive</p> Signup and view all the answers

    Match the following ions with their sources in aqueous copper sulfate:

    <p>Cu2+ = Copper sulfate SO42– = Copper sulfate H+ = Water OH– = Water</p> Signup and view all the answers

    What product is formed at the cathode during the electrolysis of copper(II)sulfate?

    <p>Copper metal (B)</p> Signup and view all the answers

    During electrolysis, OH– ions are discharged at the cathode.

    <p>False (B)</p> Signup and view all the answers

    The half equation for the reaction at the cathode is _____ + 2e– → Cu.

    <p>Cu2+</p> Signup and view all the answers

    Match the following reactions with their corresponding electrode:

    <p>Cu2+ + 2e– → Cu = Cathode 4OH– ⟶ O2 + 2H2O + 4e– = Anode</p> Signup and view all the answers

    Which ion is attracted to the anode?

    <p>Anion (D)</p> Signup and view all the answers

    Cations are negatively charged ions attracted to the anode.

    <p>False (B)</p> Signup and view all the answers

    What mnemonic can be used to remember the charge of electrodes during electrolysis?

    <p>PANIC</p> Signup and view all the answers

    During electrolysis, positive ions move towards the ______.

    <p>cathode</p> Signup and view all the answers

    Match the following terms with their corresponding descriptions:

    <p>Anion = Negatively charged ion Cation = Positively charged ion Cathode = Negative electrode Anode = Positive electrode</p> Signup and view all the answers

    What forms at the cathode during the electrolysis of metals?

    <p>Metals or hydrogen gas (A)</p> Signup and view all the answers

    Electrolysis requires a supply of electrons at the anode.

    <p>False (B)</p> Signup and view all the answers

    What are the charge carriers in the external circuit during electrolysis?

    <p>Electrons</p> Signup and view all the answers

    What is the primary function of an electrolyte in electrolysis?

    <p>To provide ions that conduct electricity (D)</p> Signup and view all the answers

    Covalent compounds can conduct electricity and undergo electrolysis.

    <p>False (B)</p> Signup and view all the answers

    What happens to ionic compounds when an electric current is passed through them while in the molten state?

    <p>They decompose or break down.</p> Signup and view all the answers

    The positive electrode in an electrolysis cell is called the ______.

    <p>anode</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Electrode = Rod through which electric current flows Ionic Compound = Conducts electricity when molten or dissolved Solid State Ionic Compound = Cannot conduct electricity Aqueous Solution = Ionic compound in water</p> Signup and view all the answers

    What does oxidation involve?

    <p>Loss of electrons (A)</p> Signup and view all the answers

    Reduction occurs at the anode.

    <p>False (B)</p> Signup and view all the answers

    What happens to negatively charged ions at the anode?

    <p>They lose electrons.</p> Signup and view all the answers

    In an ionic half-equation, reduction shows the gain of ______.

    <p>electrons</p> Signup and view all the answers

    Match the following types of ions with their respective behavior during electrolysis:

    <p>Anode = Loses electrons Cathode = Gains electrons Metal ions = Become metal atoms Non-metal ions = Become neutral substances</p> Signup and view all the answers

    Which ionic half-equation represents the reduction of copper ions?

    <p>Cu2+ + 2e– → Cu (C)</p> Signup and view all the answers

    Ionic half-equations must show both oxidation and reduction in a single equation.

    <p>False (B)</p> Signup and view all the answers

    What does a charge of '+2' on an ion indicate regarding the number of electrons gained upon reduction?

    <p>2 electrons</p> Signup and view all the answers

    Flashcards

    Electrolysis

    A chemical process that uses electricity to drive non-spontaneous chemical reactions.

    Anode

    The positively charged electrode in an electrolytic cell where oxidation occurs.

    Cathode

    The negatively charged electrode in an electrolytic cell where reduction occurs.

    Reactivity Series

    The order of metals based on their reactivity towards other substances, with the most reactive at the top.

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    Aqueous Metal Solution

    A solution containing a metal's ions, such as Cu2+ in copper sulfate solution.

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    Electrolyte

    A substance that conducts electricity when molten or dissolved in water because it contains free ions that can carry the charge.

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    Electrode

    A rod of metal or graphite that allows an electric current to flow into or out of the electrolyte.

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    Why covalent compounds don't undergo electrolysis

    Covalent compounds do not conduct electricity because they do not have free ions to carry the charge. Therefore, they cannot undergo electrolysis.

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    Anion

    A negatively charged ion that is attracted to the anode during electrolysis.

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    Cation

    A positively charged ion that is attracted to the cathode during electrolysis.

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    Charge transfer

    The movement of charge carriers, like electrons in wires and ions in electrolytes, to enable the flow of current.

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    Current

    The rate of flow of charge.

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    Why does the anode decrease in Mass during Electrolysis?

    The mass of the anode decreases during electrolysis because metal atoms lose electrons and become ions, which then move into the solution.

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    Why is the Anode Mass Loss Equal to the Cathode Mass Gain?

    The mass gained by the cathode is equal to the mass lost by the anode. This is because the metal ions gained electrons, become neutral atoms, and deposit onto the cathode.

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    Why is copper deposited at the cathode during electrolysis of copper(II) sulfate?

    In electrolysis, the less reactive ion is discharged at the cathode. This means the ion gains electrons (is reduced) and turns into a neutral atom, forming a metal deposit on the electrode.

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    What causes the cathode to increase in mass during electrolysis?

    In electrolysis, copper ions (Cu2+) are reduced at the cathode, meaning they gain electrons and become copper atoms, which then deposit on the electrode, increasing its mass.

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    What is the half-equation for the reaction at the cathode?

    The half-equation for the reaction at the cathode during electrolysis of copper(II) sulfate is: Cu2+ + 2e- → Cu. This shows that copper ions gain two electrons to become neutral copper atoms.

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    What is discharged at the anode during the electrolysis of copper(II) sulfate?

    In electrolysis of copper(II) sulfate, hydroxide ions (OH-) are discharged at the anode. This means they lose electrons and are oxidized to form oxygen gas.

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    How is oxygen gas produced at the anode during electrolysis?

    Oxygen gas is produced at the anode during the electrolysis of copper(II) sulfate because hydroxide ions (OH-) are oxidized. The half-equation for this reaction is: 4OH- → O2 + 2H2O + 4e-. This shows the formation of oxygen gas, water, and the loss of electrons.

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    Oxidation

    The loss of electrons by an atom or ion.

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    Reduction

    The gain of electrons by an atom or ion.

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    Redox reaction

    A chemical reaction that involves the transfer of electrons.

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    Ionic half-equation

    A chemical equation representing only half of the overall redox reaction, showing either the gain or loss of electrons.

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    Metal ion reduction

    A positively charged ion that gains electrons during electrolysis to become a neutral atom.

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    Non-metal ion oxidation

    A negatively charged ion that loses electrons during electrolysis to become a neutral atom or molecule.

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    Study Notes

    Electrolysis Principles

    • Electrolysis is the process of decomposing a compound using an electric current
    • Molten ionic compounds and aqueous solutions of ionic compounds can be electrolysed
    • Covalent compounds cannot be electrolysed as they do not conduct electricity in the solid or liquid state
    • Ions in ionic compounds can move and carry charge when molten or dissolved in solution, allowing them to conduct electricity

    Electrical Conductivity of Ionic Compounds

    • Solid ionic compounds do not conduct electricity because the ions are fixed in place.
    • Molten or dissolved ionic compounds conduct electricity because the ions are free to move.

    Key Terms in Electrolysis

    • Electrode: A rod of metal or graphite conducting an electrical current into or out of an electrolyte.
    • Electrolyte: A molten or dissolved ionic compound that conducts electricity.
    • Anode: The positive electrode in an electrolysis cell
    • Cathode: The negative electrode in an electrolysis cell
    • Anion: A negatively charged ion, attracted to the anode.
    • Cation: A positively charged ion, attracted to the cathode

    Electrolysis Principles - Extended Tier

    • During electrolysis, a current flows around a circuit requiring charge to be carried
    • Power supply provides electrons to the cathode, making it negatively charged
    • Positive ions (cations) in the electrolyte move towards the cathode, where they gain electrons
    • Negative ions (anions) in the electrolyte move towards the anode, where they lose electrons
    • Electrons move from the anode back to the power supply, completing the circuit
    • Electrons are charge carriers in the external circuit, while ions are charge carriers within the electrolyte.

    Electrolysis of Molten Compounds (e.g., Lead(II) Bromide)

    • A binary ionic compound is made of two elements joined by ionic bonds
    • Electrolysis of molten lead (II) bromide produces lead metal at the cathode and bromine gas at the anode
    • To heat up the substance and allow the ions to move and conduct electricity
    • Adding lead(II) bromide into a beaker, and heating up until molten
    • Placing two graphite rods as electrodes and connecting them to a power pack or battery
    • Turning on the power pack to allow electrolysis

    Electrolysis of Aqueous Solutions (e.g., Sodium Chloride)

    • Brine is a concentrated solution of sodium chloride
    • Electrolysis using inert electrodes (e.g., platinum or graphite) as they do not participate in the reaction
    • Ions present in brine are Na+, Cl-, H+, and OH-
    • Electrolysis produces hydrogen gas at the cathode and chlorine gas at the anode.
    • Sodium hydroxide remains in the solution.

    Electrolysis of Dilute Sulfuric Acid

    • Electrolysis of dilute sulfuric acid uses inert electrodes to create hydrogen gas at the cathode and oxygen gas at the anode.
    • The ions present are H+, SO4-2, and H2O, which dissociates to H+ and OH-

    Electrolysis of Aqueous Copper Sulfate

    • Electrolysis of aqueous copper sulfate uses inert electrodes.
    • Copper is produced at the cathode and oxygen gas is produced at the anode
    • The cathode increases in mass as copper atoms are deposited onto it
    • The anode decreases in mass.

    Ionic Half-Equations (Extended Tier Only)

    • Oxidation is the loss of electrons, reduction is the gain of electrons
    • Ions in electrolysis will gain or lose electrons at electrodes
    • Half-equations show the exact electron gain or loss during a redox reaction at an electrode.
    • Ions are reduced at the cathode and oxidised at the anode; this produces new neutral atoms in the products.

    Writing Ionic Half-Equations

    • Metals are positive ions (e.g., Li+, Cu2+, Al3+)
    • For non-metals (e.g., Cl-, Br-, OH-)
    • Important in electrochemistry
    • Hydrogen ions/hydrogen half-equation
    • Halide ions/halogen half equation
    • Hydroxide ion/oxygen half-equation

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