Chemistry Redox Reactions Overview
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Questions and Answers

In the reaction, MnO4^- + 5Fe^2+ + 8H^+ → Mn^2+ + 5Fe^3+ + ______

4H2O

Oxidation involves an increase in ______ number.

oxidation

In the reaction Cd + H^+ + NO3^- → Cd^2+ + NO + ______, nickel oxide is produced.

H2O

The reducing agent in the reaction is ______.

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

In the redox reaction 8Al + 3Fe3O4 → 4Al2O3 + 9Fe, ______ is reduced.

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

Oxidation occurs when an element loses ______.

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

Reduction occurs when an element gains ______.

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

In the reaction 2Na + Cl2, each Na loses one ______.

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

Zn acts as a ______ agent by donating electrons to Cu^2+.

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

Cu^2+ is an example of an ______ agent.

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

The oxidation number of any un-combined element is ______.

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

In the equation for the disinfecting of water, Cl2 is the ______ agent.

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

Oxidation and reduction reactions are also known as ______ reactions.

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

An un-combined element is an element that is not bonded to another element, e.g., Zn, Fe, ______.

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

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

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

The sum of the oxidation numbers of all of the elements in a compound must add up to ______.

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

Oxygen always has an oxidation number of ______ except in peroxides and in the compound OF2.

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

Hydrogen is always assigned an oxidation number of ______ in its compounds except in the metal hybrids.

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

Cu + 2H2SO4 produces CuSO4 and SO2 with the formation of ______.

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

The halogens always have an oxidation number of ______ in their compounds unless bonded to a more electronegative atom.

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

When an element is oxidised, its oxidation number ______, indicating an increase in its oxidation state.

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

Sulfuric acid acts as the ______ agent in oxidation-reduction reactions.

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

The oxidation number of sulphur in Na2S2O3 is ______.

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

In the reaction of potassium bromide with chlorine water, the solution turns a yellow/orange color due to the formation of ______.

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

Chlorine displaces bromine from a solution of a ______ salt.

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

The addition of barium chloride solution to the test tube results in a ______ precipitate when sulfate ions are present.

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

Bromine can oxidise iodide ions, confirming that it is a ______ agent.

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

When chlorine water is added to sodium sulfite solution, no ______ change is observed initially.

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

The reddish-brown color in potassium iodide solution is due to the formation of ______.

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

The greenish-brown precipitate observed confirms the presence of ______ ions.

<p>Fe3+</p> Signup and view all the answers

When magnesium is placed in copper sulfate solution, it displaces ______ from the solution.

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

The oxidation half-equation for iron(II) sulfate is ______ -> Fe3+ + 2e-.

<p>Fe2+</p> Signup and view all the answers

The reaction involving zinc and copper sulfate demonstrates that zinc has a greater tendency to ______ electrons than copper.

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

In the redox reaction, MnO4- is reduced to Mn2+ which involves the gain of ______ electrons.

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

The process of balancing the redox equation ensures that the number of ______ gained equals the number of electrons lost.

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

During the experiment, no apparent change occurs when chlorine water is added to the iron(II) sulfate solution until ______ is added.

<p>sodium hydroxide</p> Signup and view all the answers

The blue color of copper sulfate solution becomes lighter because magnesium displaces Cu2+ ions, leading to a ______ solution.

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

Flashcards

Oxidation

The process of losing electrons by an element.

Reduction

The process of gaining electrons by an element

Redox reaction

A reaction where oxidation and reduction occur simultaneously.

Oxidizing agent

A substance that causes oxidation in another substance.

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Reducing agent

A substance that causes reduction in another substance.

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Oxidation number

The apparent charge on an atom in a chemical compound.

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Uncombined Element Oxidation Number

The oxidation number of an element that is not bonded to anything else is zero.

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OILRIG

Acronym for remembering oxidation and reduction: Oxidation is Loss, Reduction is Gain of electrons

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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

Usually -2, except in peroxides and OFâ‚‚.

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Oxidation number of Hydrogen

+1 in compounds, except in metal hydrides (where it's -1).

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Oxidation number of Halogens

-1 in compounds unless bonded to a more electronegative atom.

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Oxidation Number Sum in Compound

The sum of oxidation numbers of all elements in a compound is zero.

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Oxidation Number Sum in Complex Ion

The sum of oxidation numbers in a complex ion equals the ion's charge.

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Halogen Oxidizing Ability

Halogens (like chlorine, bromine, iodine) have decreasing oxidizing power down the group.

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Chlorine Displaces Bromine

Chlorine is a stronger oxidizing agent than bromine, so it will replace bromine in a chemical reaction.

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Iodide Oxidation by Bromine

Bromine can oxidize iodide ions to iodine.

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Sulfate Test

Barium chloride solution precipitates sulfate ions as a white precipitate, which doesn't dissolve in dilute hydrochloric acid.

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What is oxidized in this welding reaction?

Aluminum (Al) is oxidized, as its oxidation number increases from 0 to +3.

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What is reduced in this welding reaction?

Iron (Fe) is reduced, as its oxidation number decreases from +8/3 to 0.

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What is the reducing agent in this welding reaction?

Aluminum (Al) is the reducing agent, as it causes the reduction of iron.

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What is the oxidizing agent in this welding reaction?

Iron oxide (Fe₃O₄) is the oxidizing agent, as it causes the oxidation of aluminum.

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What is the role of oxidation numbers in redox reactions?

Oxidation numbers help us identify which elements are oxidized and reduced in a redox reaction, as they represent the apparent charge of an atom in a compound.

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What is the relationship between oxidation and reduction?

Oxidation and reduction always occur simultaneously in a chemical reaction. One substance loses electrons (oxidation), while another substance gains electrons (reduction).

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What is the role of chlorine water in the reaction with iron(II) sulfate?

Chlorine water acts as an oxidizing agent, causing iron(II) ions (Fe^2+^) to lose electrons and become iron(III) ions (Fe^3+^).

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How is the presence of Fe^3+^ ions confirmed?

The formation of a greenish-brown precipitate (Fe2O3) when dilute NaOH is added indicates the presence of Fe3+^ ions.

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What is a displacement reaction?

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

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Why does zinc react with copper sulfate solution?

Zinc has a greater tendency to lose electrons than copper, so it forces the Cu^2+^ ions in the solution to gain electrons and become copper metal.

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What happens to the magnesium ribbon in copper sulfate solution?

Magnesium, being more reactive than copper, displaces copper from the solution, forming a coating of copper metal on the magnesium ribbon.

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How to balance redox equations using oxidation numbers?

  1. Assign oxidation numbers to all elements in the equation. 2) Identify elements that change oxidation number. 3) Write half-reactions showing electron loss and gain. 4) Balance the half-reactions so that the number of electrons lost equals the number gained.
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What is the purpose of balancing redox equations?

Balancing redox equations ensures that the number of atoms and the charge are equal on both sides of the equation, reflecting the conservation of mass and charge.

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Study Notes

Oxidation and Reduction

  • Oxidation: Loss of electrons
  • Reduction: Gain of electrons
  • OILRIG: Oxidation Is Loss, Reduction Is Gain
  • Oxidation and reduction always occur together
  • Redox reactions involve both oxidation and reduction

Oxidising Agents

  • A substance that brings about oxidation in other substances
  • Always reduced in the process

Reducing Agents

  • A substance that brings about reduction in other substances
  • Always oxidized in the process

Examples of Redox Reactions

  • 2Mg + O2 → 2MgO (Magnesium oxidized, oxygen reduced)
  • Cu2+ + H2 → Cu + H2O (Cu2+ reduced, H2 oxidized)
  • 2Na + Cl2 → 2NaCl (Sodium oxidized, chlorine reduced)

Oxidation Numbers

  • The charge an atom has or appears to have when electrons are distributed
  • Important in tracking electrons during chemical reactions involving covalent compounds

Rules for Assigning Oxidation Numbers

  • Uncombined elements have an oxidation number of 0
  • Ions have oxidation numbers equal to their charge
  • The sum of oxidation numbers in a compound is zero
  • Oxygen usually has an oxidation number of -2 (except in peroxide compounds and OF2)
  • Hydrogen usually has an oxidation number of +1 (except in metal hydrides)
  • Halogens usually have an oxidation number of -1

Oxidation and Reduction in Terms of Oxidation Numbers

  • Oxidation: Increase in oxidation number
  • Reduction: Decrease in oxidation number

Examples of Oxidation and Reduction in Reactions

  • Cu + 2H2SO4 → CuSO4 + SO2 + 2H2O (Cu oxidized; H2SO4 reduced)
  • Chlorine reacts with potassium bromide solution (or potassium iodide) which demonstrates the oxidative ability of chlorine (or bromine)

The Oxidising Ability of the Halogens

  • Chlorine displaces bromine from a solution of a bromide salt
  • Chlorine displaces iodine from a solution of an iodide salt
  • Bromine displaces iodine from a solution of an iodide salt
  • A halogen will oxidise the ions of any other halogen below it in the group

Displacement Reactions of Metals

  • Zinc displaces copper from copper sulfate solution, forcing copper atoms to accept electrons from zinc

Balancing Redox Equations

  • A step-by-step method to balance redox reactions using oxidation numbers. This method is shown in the example of balancing MnO4- + Fe2+ + H+ → Mn2+ + Fe3+ + H2O.

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Oxidation and Reduction PDF

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Test your understanding of oxidation and reduction in chemistry with this quiz. Explore important concepts like oxidizing and reducing agents, as well as oxidation numbers. Perfect for students studying redox reactions and their applications.

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