Electrolysis of Aqueous Solutions
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Electrolysis of Aqueous Solutions

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Questions and Answers

What occurs when a metal is above hydrogen in the reactivity series during electrolysis?

  • The more reactive metal precipitates out.
  • The less reactive metal ions are discharged.
  • Only copper ions are attracted to the cathode.
  • Hydrogen ions are discharged instead of metal ions. (correct)

    • Which ions are present in aqueous copper sulfate solution?

  • Cu+, SO4–, H+, OH–
  • Cu2+, SO42–, H+, OH– (correct)
  • Cu+, SO42–, H2O, OH–
  • Cu2+, SO42–, H2O, OH–

    • What happens at the cathode during the electrolysis of copper(II) sulfate with graphite electrodes?

  • Copper ions are discharged and reduced to form copper metal. (correct)
  • The copper ions are oxidized.
  • Hydrogen gas is produced.
  • The SO42– ions are reduced.

    • What is the observable product at the cathode when performing electrolysis of copper(II) sulfate?

    <p>Copper metal plating.</p> Signup and view all the answers

    What determines the ion that will be discharged at the cathode during electrolysis?

    <p>The reactivity of the ions in relation to each other.</p> Signup and view all the answers

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

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

    What happens to the mass of the cathode during electrolysis with copper electrodes?

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

    What ions are primarily responsible for forming oxygen gas at the anode?

    <p>OH– ions</p> Signup and view all the answers

    Which half equation represents the reaction taking place at the anode?

    <p>4OH– ⟶ O2 + 2H2O + 4e–</p> Signup and view all the answers

    During electrolysis, what happens to the concentration of Cu2+ ions in solution?

    <p>Remains constant</p> Signup and view all the answers

    What is observed at the anode during the electrolysis of a dilute sodium chloride solution?

    <p>Formation of chlorine gas</p> Signup and view all the answers

    What is the relationship between the mass gained by the cathode and the mass lost by the anode?

    <p>Mass gained equals mass lost</p> Signup and view all the answers

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

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

    What process occurs at the anode during electron transfer reactions?

    <p>Oxidation of negatively charged ions</p> Signup and view all the answers

    In ionic half-equations, what must be balanced?

    <p>Atoms and charges</p> Signup and view all the answers

    What characterizes reduction in the context of electrochemistry?

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

    Which of the following represents the ionic half-equation for the reduction of aluminum ions?

    <p>Al3+ + 3e– → Al</p> Signup and view all the answers

    Which of the following ions is typically a negative ion in electrochemistry?

    <p>Cl–</p> Signup and view all the answers

    What is the result when metal ions gain electrons during electrolysis?

    <p>Formation of metal atoms</p> Signup and view all the answers

    What does the charge on a metal ion indicate in terms of the number of electrons gained?

    <p>The number of electrons that will be gained</p> Signup and view all the answers

    Which ionic half-equation correctly depicts the oxidation of copper ions?

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

    What happens to hydrogen ions during the electrolysis process?

    <p>They gain electrons to become hydrogen gas.</p> Signup and view all the answers

    In the electrolysis of concentrated aqueous sodium chloride, what is the reaction occurring at the anode?

    <p>2Cl– → Cl2 + 2e–</p> Signup and view all the answers

    Which of the following equations represents the oxidation of hydroxide ions during electrolysis?

    <p>4OH– → O2 + 2H2O + 4e–</p> Signup and view all the answers

    What method can be used to remember the definition of oxidation and reduction?

    <p>OIL RIG</p> Signup and view all the answers

    In the half-equation of halide ions oxidising to their respective halogens, what is the correct representation?

    <p>2X– → X2 + 2e–</p> Signup and view all the answers

    Which species is reduced during the electrolysis of dilute sulfuric acid?

    <p>Hydrogen ions</p> Signup and view all the answers

    Identify the product formed at the cathode during electrolysis of molten lead(II) bromide.

    <p>Lead metal</p> Signup and view all the answers

    Which statement accurately describes reduction in the context of electrolysis?

    <p>Gain of electrons occurs.</p> Signup and view all the answers

    What is the test for identifying oxygen gas?

    <p>A glowing splint will relight when dipped into the gas.</p> Signup and view all the answers

    During the electrolysis of a concentrated halide solution, what is produced at the anode?

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

    What will happen when a dilute halide solution is electrolyzed?

    <p>Oxygen gas will be produced at the anode.</p> Signup and view all the answers

    Which ions are attracted to the positive electrode during electrolysis?

    <p>Negatively charged OH– ions and non-metal ions</p> Signup and view all the answers

    What is the role of water in the electrolysis of aqueous solutions?

    <p>Water provides H+ and OH– ions that influence the electrolysis process.</p> Signup and view all the answers

    What happens when hydroxide ions are present and no halide ions are available during electrolysis?

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

    What determines which ions get discharged during the electrolysis of an aqueous solution?

    <p>The concentration of the ions and their relative reactivity.</p> Signup and view all the answers

    At the negative electrode (cathode), which species are attracted?

    <p>Positively charged H+ and metal ions</p> Signup and view all the answers

    In a concentrated solution of barium chloride, which ion is discharged preferentially at the anode?

    <p>Chloride ions</p> Signup and view all the answers

    What sound is produced when hydrogen gas is present during electrolysis?

    <p>A popping sound</p> Signup and view all the answers

    Study Notes

    Electrolysis of Aqueous Solutions

    • Electrolysis of aqueous solutions always involves water molecules dissociating to form hydrogen and hydroxide ions.
    • The presence of these ions influences the electrolysis process.
    • During electrolysis of aqueous solutions, the ions discharged at each electrode depend on the reactivity of the elements involved.
    • Concentration of the solution can affect the products of electrolysis.

    Anode

    • At the anode (positive electrode), negatively charged ions like hydroxide and non-metal ions are attracted.
    • If halide ions (Cl-, Br-, I-) are present, the corresponding halogen is produced at the anode as they lose electrons.
    • In the absence of halide ions but presence of hydroxide ions, oxygen gas is produced at the anode as hydroxide ions lose electrons.
    • The concentration of the solution influences the discharged ion. A concentrated halide solution yields halogen at the anode, while a dilute halide solution yields oxygen.

    Cathode

    • At the cathode (negative electrode), positively charged hydrogen and metal ions are attracted.
    • The less reactive ion will be discharged at the cathode.
    • If the metal is more reactive than hydrogen, hydrogen gas will be produced.
    • If the metal is less reactive than hydrogen, the metal itself will be produced and plated onto the cathode.

    Reactivity Series

    • The reactivity series of metals helps determine which ion will be discharged at the cathode during electrolysis.

    Electrolysis of Aqueous Copper Sulfate

    • Aqueous copper sulfate contains copper and sulfate ions from the salt and hydrogen and hydroxide ions from water.
    • Using graphite electrodes:
      • Copper ions are discharged at the cathode as they are less reactive than hydrogen, forming copper metal.
      • Hydroxide ions are discharged at the anode, forming oxygen gas.
    • Using copper electrodes:
      • The cathode gains mass as copper ions are reduced to copper atoms.
      • The anode loses mass as copper atoms are oxidized to copper ions.
      • The mass gain at the cathode equals the mass loss at the anode, indicating that the copper deposited on the cathode originates from the anode.

    Products of Common Aqueous Solutions

    • Concentrated sodium chloride (NaCl) solution: chlorine gas at the anode and hydrogen gas at the cathode.
    • Dilute sodium chloride (NaCl) solution: oxygen gas at the anode and hydrogen gas at the cathode.
    • Concentrated aqueous copper sulfate (CuSO4) solution: oxygen gas at the anode and copper at the cathode.
    • Dilute sulfuric acid (H2SO4): oxygen gas at the anode and hydrogen gas at the cathode.

    Ionic Half Equations

    • Electrochemistry involves the transfer of electrons, leading to the oxidation-reduction reactions.
    • Oxidation is the loss of electrons, occurring at the anode.
    • Reduction is the gain of electrons, occurring at the cathode.
    • Ionic half-equations represent the partial reactions, showing either the loss or gain of electrons.
    • These equations must be balanced in terms of atoms and charges.

    Writing Ionic Half-Equations

    • Metals: Metal ions gain electrons to form metal atoms during reduction.
    • Non-metals: Non-metal ions lose electrons to form non-metal atoms during oxidation.
    • Hydrogen ion (H+): Two hydrogen ions gain two electrons to form hydrogen gas (H2) during reduction.
    • Halide ion (X-): Two halide ions lose two electrons to form a halogen molecule (X2) during oxidation.
    • Hydroxide ion (OH-): Four hydroxide ions lose four electrons to form oxygen gas (O2) and water (H2O) during oxidation.

    Table of Reduction and Oxidation Reactions

    • Electrolysis of Molten Lead(II) Bromide (PbBr2):
      • Anode: 2Br- → Br2 + 2e-
      • Cathode: Pb2+ + 2e- → Pb
    • Electrolysis of Concentrated Aqueous Sodium Chloride (NaCl):
      • Anode: 2Cl- → Cl2 + 2e-
      • Cathode: 2H+ + 2e- → H2
    • Electrolysis of Dilute Sulfuric Acid (H2SO4):
      • Anode: 4OH- → O2 + 2H2O + 4e-
      • Cathode: 2H+ + 2e- → H2

    Mnemonic Devices

    • OIL RIG: Oxidation Is Loss (of electrons); Reduction Is Gain (of electrons).
    • RED CAT: REDuction at the CAThode.
    • AN OX: ANode for OXidation.

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    CIE IGCSE Chemistry Electrolysis PDF

    Description

    Explore the fascinating process of electrolysis in aqueous solutions. This quiz covers the behavior of ions at both the anode and cathode, and how concentration affects the products formed. Challenge your understanding of this fundamental chemical reaction.

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