CHM1311 Oxidation States and Redox Reactions
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Questions and Answers

What type of reaction involves the transfer of a proton?

  • Redox reaction
  • Acid-base reaction (correct)
  • Precipitation reaction
  • Combination reaction
  • In the reaction Zn (s) + Cu2+ (aq) → Zn2+ (aq) + Cu (s), which process occurs?

  • Precipitation
  • Reduction
  • Oxidation (correct)
  • Acid-base reaction
  • What does an oxidation state represent?

  • A theoretical parameter of electron bookkeeping (correct)
  • The number of protons in an atom
  • An observable property of a chemical reaction
  • The actual charge of an atom in a molecule
  • What is the oxidation state of Cl in HCl?

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

    When assigning oxidation states, what should you do if two rules contradict each other?

    <p>Follow the rule that appears higher on the list</p> Signup and view all the answers

    In the reaction NaI (aq) + AgNO3 (aq) → NaNO3 (aq) + AgI (s), what type of reaction is represented?

    <p>Precipitation reaction</p> Signup and view all the answers

    What does the charge of an atom calculate as?

    <p>#protons - #electrons</p> Signup and view all the answers

    What is the oxidation state of sodium (Na) when it forms Na+?

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

    What is the oxidation state of sulfur in S8?

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

    What is the oxidation state of phosphorus in P2O5?

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

    What is the oxidation state of chromium in CrO4^2-?

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

    What is the oxidation state of calcium in CaH2?

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

    In which of the following does hydrogen have an oxidation state of –1?

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

    What is the oxidation state of carbon in CO?

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

    What is the oxidation state of oxygen in SO2?

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

    What is the oxidation state of xenon in XeF4?

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

    What is the primary purpose of adding H+ ions during the balancing of half-reactions in acidic solution?

    <p>To balance the number of hydrogen atoms</p> Signup and view all the answers

    In a basic solution, what modification is made to the balancing procedure involving H+ ions?

    <p>For each H+, an OH– is added to both sides</p> Signup and view all the answers

    When combining H+ and OH– ions during the balancing process, what compound is formed?

    <p>Water (H2O)</p> Signup and view all the answers

    What is the function of the electrons in the balancing of half-reactions?

    <p>To balance the net charge on each side</p> Signup and view all the answers

    Which step may be necessary before combining the two half-reactions in redox reactions?

    <p>Multiplying the half-reactions by the least common denominator</p> Signup and view all the answers

    What is the process by which a substance loses electrons called?

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

    Which statement correctly describes an oxidizing agent?

    <p>It causes oxidation in another reactant.</p> Signup and view all the answers

    In the reaction Zn + Cu2+ → Zn2+ + Cu, which species is the reducing agent?

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

    What happens to the oxidation state of a reducing agent in a redox reaction?

    <p>It increases.</p> Signup and view all the answers

    Which of the following is a characteristic of reduction in redox reactions?

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

    In the half-reaction Zn → Zn2+ + 2 e–, what does the zinc atom do?

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

    For the reaction represented as 2Fe + 3CO2 → Fe2O3 + 3C, what is the role of Fe?

    <p>It is reduced.</p> Signup and view all the answers

    What mnemonic aids in remembering the concepts of oxidation and reduction?

    <p>LEO says GER</p> Signup and view all the answers

    What is the first step in the half-equation method for balancing redox reactions?

    <p>Write out the net ionic form of the reaction</p> Signup and view all the answers

    In the oxidation process, what happens to the oxidation state of copper (Cu) when it is transformed from Cu(s) to Cu2+(aq)?

    <p>It increases</p> Signup and view all the answers

    Which species is being reduced in the reaction where Cu(s) reacts with NO3–(aq) to form Cu2+(aq) and NO(g)?

    <p>NO3–</p> Signup and view all the answers

    What is the purpose of adding electrons to balance the half-reaction?

    <p>To balance the charges on both sides</p> Signup and view all the answers

    In an acidic solution, how would you balance the half-reaction ClO2(g) → ClO3–(aq)?

    <p>By adding H+ and H2O</p> Signup and view all the answers

    What happens to nitrogen (N) in the given redox reaction of Cu(s) with NO3–(aq)?

    <p>It is reduced</p> Signup and view all the answers

    When balancing the overall redox reaction, how do you ensure that the number of atoms and charges are equal on both sides?

    <p>By adjusting the coefficients of the reactants and products</p> Signup and view all the answers

    Which step is NOT involved in balancing redox reactions using the half-equation method?

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

    Study Notes

    Chemical Reactions Categories

    • Acid-Base Reaction: Involves proton transfer, e.g., HCl + H2O → H3O+ + Cl–.
    • Precipitation Reaction: Formation of a solid, e.g., NaI + AgNO3 → NaNO3 + AgI(s).
    • Redox Reaction: Involves transfer of electrons, e.g., Zn + Cu2+ → Zn2+ + Cu.

    Oxidation States and Electron Transfer

    • Oxidation State: A theoretical charge on an atom if electrons were removed from bonds.
    • Calculated as the difference between the number of protons and electrons.
    • Common oxidation states: H (+1), O (–2), Na (+1), F (–1).

    Determining Oxidation States

    • Follow specific rules to assign oxidation states, prioritize higher rules if contradictory.
    • For polyatomic ions, calculate oxidation numbers using the overall charge.

    Half-Reaction Method

    • Separation of Reactions: Redox reactions can be split into oxidation and reduction half-reactions.
    • Balance elements, then balance oxygen by adding H2O and hydrogen by adding H+.
    • Charge is balanced by adding electrons.

    Examples of Oxidation States Calculation

    • In S8, S = 0 because it's a pure element.
    • In P2O5, P = +5 and O = –2.
    • In CrO42–, Cr = +6 and O = –2.
    • In CaH2, Ca = +2 and H = –1 (as part of a hydride).

    Redox Agents

    • Oxidizing Agent: Causes oxidation in another species, itself reduced (oxidation state decreases).
    • Reducing Agent: Causes reduction in another species, itself oxidized (oxidation state increases).

    Oxidation and Reduction Terminology

    • Oxidation: Loss of electrons (OIL - Oxidation Is Loss).
    • Reduction: Gain of electrons (RIG - Reduction Is Gain).
    • Example: Zn oxidizes to Zn2+, while Cu2+ reduces to Cu.

    Example Redox Reactions

    • In reaction: Cu + NO3– → Cu2+ + NO, Cu is oxidized, and nitrogen in nitrate is reduced.
    • Overall reactions, such as those involving manganese (MnO4–), often require balancing steps.

    Balancing Redox Reactions

    • For acidic solution, followed by adding water and H+ ions.
    • In basic solutions, add OH– for each H+, simplifying when combined.

    Lead Oxidation in Environmental Testing

    • Example reaction: Pb + MnO4– → Pb2+ + Mn2+.
    • Percent composition calculation involves understanding the stoichiometry of the reaction and the mass of lead oxidized in the soil sample.

    Additional Concepts

    • Monitoring oxidation states helps to identify agents and balance reactions in various mediums.
    • The practical application of these concepts can be observed in environmental chemistry and industrial practices.

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    Description

    This quiz focuses on the fundamental concepts of oxidation states and redox reactions as covered in CHM1311. Key chemical reactions such as acid-base, precipitation, and redox are explored through various examples. Test your understanding of electron transfer and reaction mechanisms in chemistry.

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