Redox Reactions and Oxidation Numbers
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Questions and Answers

What is the oxidation number of element B in the compound A-B if B is the more electronegative element?

-1

The oxidation number of O in H2O is -1.

False

In the compound Ni(CO)4, what is the oxidation number of Ni?

  • -2
  • 2
  • 0 (correct)
  • -1

    • In a bond between two identical atoms, such as Cl-Cl, the oxidation number of each atom is _____ .

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

    Match the compounds with their respective oxidation numbers of oxygen (O.N.):

    <p>H2O = -2 H2O2 = -1 OF2 = +2 O2F2 = +1</p> Signup and view all the answers

    What is the oxidation number of sulfur in SO3?

    <p>6</p> Signup and view all the answers

    The oxidation number of oxygen can be +2 in the compound OF2.

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

    What is the oxidation number of nitrogen in HNO3?

    <p>+5</p> Signup and view all the answers

    In the compound H2S, the oxidation number of hydrogen is ______.

    <p>-1</p> Signup and view all the answers

    Match the following elements with their oxidation numbers in specific compounds:

    <p>H in H2O2 = -1 S in SO2 = +4 N in N2O5 = +5 O in OF2 = +2</p> Signup and view all the answers

    What is the oxidation number of sodium in NaCl?

    <p>+1</p> Signup and view all the answers

    The oxidation number of an atom in its free state is always zero.

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

    What does a positive oxidation number indicate?

    <p>An atom has lost electrons.</p> Signup and view all the answers

    The oxidation number of Mg in MgCl2 is _____

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

    What is the oxidation number of oxygen in O2?

    <p>0</p> Signup and view all the answers

    The oxidation number of an element can only be positive.

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

    Match the following atoms with their respective oxidation numbers as ions:

    <p>Na+ = +1 Mg2+ = +2 Cl- = -1 O2- = -2</p> Signup and view all the answers

    In a molecule, shared electrons belong entirely to the _____ atom.

    <p>more electronegative</p> Signup and view all the answers

    What happens to sodium (Na) in the reaction where it is oxidized?

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

    Reduction is the process of losing electrons.

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

    What is the role of an oxidising agent in a redox reaction?

    <p>An oxidising agent accepts electrons and is reduced.</p> Signup and view all the answers

    In the reaction 2Cl- → Cl2 + 2e-, the chloride ions are __________.

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

    Match the following species with their corresponding changes in charge:

    <p>Na+ = Decrease in positive charge Cu2+ = Gain of two electrons to become Cu Fe3+ = Gain of one electron to become Fe2+ S2- = Loss of two electrons to become S</p> Signup and view all the answers

    What is the result of oxidation in a chemical reaction?

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

    A reducing agent is an electron acceptor.

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

    What happens to Fe2+ in the reaction Zn + Fe2+ → Zn2+ + Fe?

    <p>Fe2+ accepts electrons and is reduced to Fe.</p> Signup and view all the answers

    Which of the following is an oxidising agent in redox reactions?

    <p>Fe2O3</p> Signup and view all the answers

    In the equation Zn + FeSO4 → ZnSO4 + Fe, Zn is oxidised.

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

    What is the oxidation half-reaction for magnesium in the equation Mg → Mg2+ + 2e-?

    <p>Mg → Mg2+ + 2e-</p> Signup and view all the answers

    The reducing agent in the reaction 3Fe3O4 + 8Al → 9Fe + 4Al2O3 is __________.

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

    Match the reducing agents with their respective reactions:

    <p>HCl = MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O KI = H2O2 + 2KI → 2KOH + I2 Al = 3Fe3O4 + 8Al → 9Fe + 4Al2O3 C = CuO + C → Cu + CO</p> Signup and view all the answers

    Which of these reactions demonstrates a reduction process?

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

    In a redox reaction, oxidation refers to the gain of electrons.

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

    In the reaction 2Na + H2 → 2NaH, which element is oxidised?

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

    Study Notes

    Redox Reactions

    • Redox reactions involve the transfer of electrons.
    • Oxidation is the loss of electrons, resulting in an increase in positive charge or a decrease in negative charge.
    • Reduction is the gain of electrons, resulting in a decrease in positive charge or an increase in negative charge.
    • Oxidation and reduction occur simultaneously.
    • An oxidizing agent (oxidant) accepts electrons and is reduced.
    • A reducing agent (reductant) donates electrons and is oxidized.
    • Ion-electron half-reactions show only oxidation or reduction, containing ions and electrons.

    Oxidation Number

    • Oxidation number represents the charge an atom would have if all bonds were ionic.
    • The oxidation number of an element in its free state is zero.
    • The oxidation number of an ion is equal to its charge.
    • The sum of oxidation numbers in a neutral molecule is zero, and in a polyatomic ion, it is equal to the ion's charge.

    Rules for Assigning Oxidation Numbers

    • Electrons in a covalent bond are assigned to the more electronegative atom.
    • Electrons are not shared between atoms of the same element.
    • The oxidation number of alkali metals (Group 1) is +1, alkaline earth metals (Group 2) is +2, and aluminum is +3 in their compounds.

    Determining Oxidation Numbers

    • Shared electrons are counted towards the more electronegative element.
    • When atoms of the same element are linked, electrons are not distributed between them.

    Examples

    • In H2O, the oxidation number of oxygen is -2.
    • In H2O2, the oxidation number of oxygen is -1.
    • In OF2, the oxidation number of oxygen is +2.
    • Reactions can be identified as redox based on changes in oxidation numbers.

    Important Notes

    • Hydrogen is usually a reducing agent, but when reacting with reactive metals, it acts as an oxidizing agent.
    • The maximum and minimum oxidation numbers of elements can be determined by their position in the periodic table.
    • The oxidation number of an element can vary in different compounds.
    • Oxidation numbers are a useful tool for understanding and balancing redox reactions.

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    Description

    This quiz covers the concepts of redox reactions, including oxidation and reduction processes, as well as the assignment of oxidation numbers. Understand how electrons are transferred and identify the roles of oxidizing and reducing agents. Test your knowledge of these fundamental concepts in chemistry.

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