Chemistry: Oxidation and Reduction Concepts
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Questions and Answers

What is the definition of oxidation in terms of electron transfer?

  • Loss of electrons (correct)
  • Gain of electrons
  • Gain of neutrons
  • Loss of protons

Which species acts as the oxidizing agent in the given reaction involving Cd and NO3?

  • NO~3~^- (correct)
  • H~2~O
  • H^+
  • Cd

In the reaction 8Al + 3Fe3O4 → 4Al2O3 + 9Fe, which element is being reduced?

  • O
  • Alloy
  • Al
  • Fe (correct)

What is the change in oxidation number for aluminum (Al) in the reaction 8Al + 3Fe3O4 → 4Al2O3 + 9Fe?

<p>0 to +3 (A)</p> Signup and view all the answers

How many molecules of water are produced in the balanced equation 3Cd + 8H^+ + 2NO3 → 3Cd^2+ + 2NO + 4H2O?

<p>4 (C)</p> Signup and view all the answers

What occurs during the oxidation of an element?

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

In the redox reaction Zn + Cu^2+ → Zn^2+ + Cu, what is the role of zinc?

<p>Reducing agent. (B)</p> Signup and view all the answers

In the reaction 2Na + Cl2 → 2Na^+ + Cl^-, what happens to the sodium atoms?

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

Which statement correctly describes an oxidising agent?

<p>It brings about reduction in other substances. (A)</p> Signup and view all the answers

What does an oxidation number of zero indicate?

<p>The atom is found in its elemental state. (A)</p> Signup and view all the answers

When chlorine is added to water to kill germs, what role does Cl2 play?

<p>Oxidising agent. (A)</p> Signup and view all the answers

What characterizes a reducing agent in a chemical reaction?

<p>It is always oxidised. (D)</p> Signup and view all the answers

In the context of oxidation and reduction, what does the acronym OILRIG stand for?

<p>Oxidation is Loss, Reduction is Gain. (D)</p> Signup and view all the answers

What is the oxidation number of the nitrogen atom in the NO3^- ion?

<p>5 (D)</p> Signup and view all the answers

What is the oxidation number of sulfur in Na2S2O3?

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

In which situation does the oxidation number of hydrogen become -1?

<p>In metal hybrids (C)</p> Signup and view all the answers

Which of the following statements about oxidation numbers is NOT correct?

<p>Oxidation is defined as a decrease in oxidation number. (A)</p> Signup and view all the answers

What is the overall charge on the complex ion if the sum of the oxidation numbers equals +3?

<p>+3 (B)</p> Signup and view all the answers

What is the oxidation number for oxygen in most of its compounds?

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

When a species is reduced, what happens to its oxidation number?

<p>It decreases. (C)</p> Signup and view all the answers

Which of the following elements can have an oxidation number higher than +1?

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

In the reaction Cu + 2H2SO4 → CuSO4 + SO2 + 2H2O, which element is oxidized?

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

What is the role of sulfuric acid in the provided reaction?

<p>It acts as an oxidizing agent. (C)</p> Signup and view all the answers

What color does potassium bromide solution turn after the addition of chlorine water?

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

Which halogen is the strongest oxidizing agent based on the displacement reactions observed?

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

What observation indicates the presence of sulfate ions in the sodium sulfite and chlorine reaction?

<p>A white precipitate with barium chloride (A)</p> Signup and view all the answers

What happens to potassium iodide when chlorine water is added?

<p>It turns reddish-brown. (B)</p> Signup and view all the answers

In the reaction between bromine water and potassium iodide, what is the product formed?

<p>I2 (D)</p> Signup and view all the answers

Which statement is true regarding the oxidizing ability of halogens?

<p>A halogen can oxidize ions of any halogen below it in the group. (B)</p> Signup and view all the answers

What type of reaction occurs when zinc is added to copper sulfate solution?

<p>Oxidation-reduction reaction (D)</p> Signup and view all the answers

What confirms the presence of Fe3+ ions when dilute sodium hydroxide solution is added?

<p>Greenish-brown precipitate (D)</p> Signup and view all the answers

Which half-equation represents the oxidation of iron(II) ions?

<p>Fe → Fe^2+ + 2e^- (A)</p> Signup and view all the answers

What happens to the color of the copper sulfate solution when magnesium ribbon is placed in it?

<p>It becomes colorless (C)</p> Signup and view all the answers

Which oxidation state change occurs for manganese in the redox reaction with Fe^2+?

<p>From +7 to +2 (D)</p> Signup and view all the answers

When chlorine water is added to iron(II) sulfate, what noticeable change occurs?

<p>No apparent change (A)</p> Signup and view all the answers

How are the electrons balanced in the oxidation and reduction half-equations?

<p>Electrons gained equal electrons lost (A)</p> Signup and view all the answers

What type of reaction is observed with magnesium and copper sulfate when magnesium displaces copper?

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

Flashcards

Oxidation

Loss of electrons by an element.

Reduction

Gain of electrons by an element.

Redox Reaction

A reaction where both oxidation and reduction occur simultaneously.

Oxidising Agent

Substance that causes another substance to lose electrons (be oxidized).

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Reducing Agent

Substance that causes another substance to gain electrons (be reduced).

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Oxidation Number

Apparent charge of an atom in a compound, following specific rules.

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Uncombined Element Oxidation Number

Zero.

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Redox reaction example

2Na + Cl₂ → 2NaCl (Sodium and chlorine react to form sodium chloride).

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Oxidation number of an ion

The oxidation number of an ion of an element is the same as its charge.

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Oxidation number of oxygen

Oxygen typically has an oxidation number of -2, except in peroxides and OF2.

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Oxidation number of hydrogen

Hydrogen's oxidation number is usually +1, but in metal hydrides, it's -1.

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Oxidation number of halogens

Halogens usually have an oxidation number of -1, unless bonded to a more electronegative atom.

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Oxidation number rule (compounds)

The sum of the oxidation numbers of all elements in a compound must equal zero.

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Oxidation number rule (complex ions)

The sum of the oxidation numbers of all elements in a complex ion must equal the charge on the ion.

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Oxidation Number Change

The change in the apparent charge of an atom in a reaction, based on the rules for assigning oxidation numbers. An increase in oxidation number indicates oxidation, while a decrease indicates reduction.

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Halogen Displacement Reaction

A reaction where a more reactive halogen displaces a less reactive halogen from its salt solution. This is due to the more reactive halogen's stronger oxidizing power.

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Chlorine as an Oxidizing Agent

Chlorine can oxidize both bromide and iodide ions, displacing them from their respective salts as bromine and iodine, respectively. This is because chlorine is more reactive (better oxidizing agent) than both bromine and iodine.

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Bromine as an Oxidizing Agent

Bromine can oxidize iodide ions, displacing them from their salt as iodine. This is because bromine is more reactive (better oxidizing agent) than iodine.

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Sulfite Oxidation by Chlorine

Chlorine can oxidize sulfite ions (SO3^2-) to sulfate ions (SO4^2-), which is confirmed by the formation of a white precipitate (barium sulfate) upon adding barium chloride solution. This reaction demonstrates the oxidizing property of chlorine.

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Barium Sulfate Precipitate

The white precipitate formed when barium chloride is added to a solution containing sulfate ions. The precipitate indicates the presence of sulfate ions, which are formed by the oxidation of sulfite ions by chlorine.

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What is oxidation in terms of oxidation number?

Oxidation is the process where the oxidation number of an atom increases.

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Identify the oxidising agent

The oxidising agent is the substance which causes another substance to be oxidised (increase oxidation number) and itself gets reduced.

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Identify the reducing agent

The reducing agent is the substance which causes another substance to be reduced (decrease oxidation number) and itself gets oxidised.

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What does it mean to balance a redox reaction?

Balancing a redox reaction involves ensuring that the number of atoms of each element and the total charge are equal on both sides of the equation.

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How are redox reactions used in welding?

Redox reactions are used in welding because they produce a large amount of heat. The reaction of aluminum with iron oxide is a typical example of this.

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Greenish-brown precipitate

Fe₂O₃ (iron(III) oxide), which forms when dilute sodium hydroxide is added to a solution containing Fe³⁺ ions, indicating the presence of iron(III) ions.

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Oxidation of Fe²⁺

The process where iron(II) ions (Fe²⁺) lose an electron and become iron(III) ions (Fe³⁺), represented by the half-reaction: 2Fe²⁺ → 2Fe³⁺ + 2e⁻.

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Reduction of Cl₂

The process where chlorine molecules (Cl₂) gain electrons to form chloride ions (Cl⁻), represented by the half-reaction: Cl₂ + 2e⁻ → 2Cl⁻.

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Displacement Reaction

A reaction where a more reactive metal displaces a less reactive metal from its compound.

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Zinc and Copper Sulfate

A displacement reaction where zinc (Zn) displaces copper (Cu) from copper sulfate solution, forming copper metal coating on zinc and a lighter blue solution.

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Magnesium and Copper Sulfate

A displacement reaction where magnesium (Mg) displaces copper (Cu) from copper sulfate solution, forming a dark brown coating on magnesium and a colorless solution.

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Balancing Redox Equations (Step 1)

Assign oxidation numbers to all elements in the equation, including those in ions and molecules.

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Balancing Redox Equations (Step 2)

Identify the elements that change their oxidation number during the reaction.

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Study Notes

Oxidation and Reduction

  • Oxidation is the loss of electrons.
  • Reduction is the gain of electrons.
  • OILRIG (Oxidation Is Loss, Reduction Is Gain)
  • Oxidation and reduction always occur together.
  • Substances that cause oxidation in other substances are oxidizing agents.
  • Substances that cause reduction in other substances are reducing agents.
  • Oxidizing agents are always reduced.
  • Reducing agents are always oxidized.
  • Chlorine is an oxidizing agent, used for disinfecting water.

Oxidation Numbers

  • Oxidation number is the charge an atom has when electrons are distributed according to rules.
  • Oxidation numbers are used to track electrons in chemical reactions, particularly covalent compounds.
  • Uncombined elements have an oxidation number of zero.
  • Ions have an oxidation number equal to their charge.
  • Oxygen generally has an oxidation number of -2, except in peroxides and OF2.
  • Hydrogen generally has an oxidation number of +1, except in metal hydrides where it's -1.
  • Halogens usually have an oxidation number of -1, except when bonded to a more electronegative atom.
  • The sum of oxidation numbers in a compound or complex ion equals the overall charge.

Oxidation and Reduction in Terms of Oxidation Numbers

  • Oxidation involves an increase in oxidation number.
  • Reduction involves a decrease in oxidation number.
  • Example reactions (from the text) are given in which oxidation numbers change in reactions, showing oxidation and reduction.
    • Copper is oxidized, becoming a reducing agent. Sulfuric acid is reduced.
    • Chlorine is an oxidizing agent.
    • Ions in the reaction of chlorine, bromine and iodine are oxidized.
    • Zinc is a reducing agent, oxidising copper ion.

Displacement Reactions of Metals

  • Zinc displaces copper from copper sulfate solution.
  • Zinc loses electrons and is oxidized.
  • Copper gains electrons and is reduced.

Balancing Redox Equations

  • Steps are given to balance redox reactions. 
  • Examples given using manganese and iron.

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Oxidation and Reduction PDF

Description

This quiz explores the fundamental concepts of oxidation and reduction, including definitions and characteristics of oxidizing and reducing agents. It also examines the importance of oxidation numbers in chemical reactions. Test your understanding of these key chemistry principles!

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