Chemistry Chapter on Redox Reactions
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Questions and Answers

What is the oxidation number of oxygen in most compounds?

  • 0
  • -2 (correct)
  • -1
  • +2

    • In a redox reaction, both oxidation and reduction processes occur simultaneously.

    True

    What must the sum of oxidation numbers equal in a neutral compound?

    0

    In the reaction Zn + CuSO₄ → ZnSO₄ + Cu, zinc is ______ and copper is ______.

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

    Match the following oxidation numbers with their corresponding elements:

    <p>Hydrogen = +1 Chlorine = -1 Sulfur in sulfates = +6 Oxygen in peroxides = -1</p> Signup and view all the answers

    Which of the following statements is true regarding the oxidation number of monoatomic ions?

    <p>It equals the ion's charge.</p> Signup and view all the answers

    The oxidation number of hydrogen is -1 when bonded to non-metals.

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

    What is the reducing agent in a redox reaction?

    <p>the element that gets oxidized</p> Signup and view all the answers

    Which of the following describes a combination reaction?

    <p>Two or more substances react to form a single new substance.</p> Signup and view all the answers

    The formula for magnesium oxide is written with magnesium as the anion.

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

    What is the result of crisscrossing the charges of ions in ionic compounds?

    <p>It identifies the combining ratios of the ions.</p> Signup and view all the answers

    In a chemical reaction, the substances that react together are called ______.

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

    Match the following types of chemical reactions with their definitions:

    <p>Combination reaction = Two or more substances produce a single new substance Decomposition reaction = A compound breaks down into simpler substances Single-replacement reaction = One element replaces another in a compound Double-replacement reaction = Two compounds exchange ions</p> Signup and view all the answers

    Which equation represents a decomposition reaction?

    <p>2H2O → 2H2 + O2</p> Signup and view all the answers

    The products of a chemical reaction always retain the same properties as the reactants.

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

    What is the primary role of balancing chemical equations?

    <p>To ensure that the number of atoms for each element is equal on both sides of the equation.</p> Signup and view all the answers

    What is produced in a combustion reaction alongside heat and light?

    <p>Carbon Dioxide</p> Signup and view all the answers

    Not all combustion reactions are classified as synthesis reactions.

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

    What general form does a simple-replacement reaction follow?

    <p>A + BC → B + AC</p> Signup and view all the answers

    In a single replacement reaction, a more reactive metal can replace a _____ or another metal in a compound.

    <p>less reactive metal</p> Signup and view all the answers

    Which of the following is an example of a single replacement reaction?

    <p>Cu + 2AgNO3 → 2Ag + Cu(NO3)2</p> Signup and view all the answers

    Match the halogens with their reactivity levels:

    <p>Fluorine = Most reactive Chlorine = Intermediate reactivity Bromine = Less reactive Iodine = Least reactive</p> Signup and view all the answers

    Fluorine is a less reactive halogen than bromine.

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

    What happens in a single replacement reaction if the free element is less reactive than the metal in the compound?

    <p>No reaction occurs.</p> Signup and view all the answers

    Which of the following atoms has a smaller atomic radius?

    <p>Silicon (Si)</p> Signup and view all the answers

    Ionization energy and atomic radius are directly proportional.

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

    What is ionization energy?

    <p>The energy required to remove an electron from an atom.</p> Signup and view all the answers

    Element X has ____ valence electrons because of the large increase in ionization energy between the second and third ionization.

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

    How does electronegativity change as you move down a group in the periodic table?

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

    Explain what shielding refers to in atomic structure.

    <p>Shielding is when core electrons block the protons from attracting valence electrons.</p> Signup and view all the answers

    Which metal is more reactive than Aluminum but less reactive than Iron?

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

    The third ionization energy is always ____ than the first and second ionization energies.

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

    Match the elements with the number of valence electrons based on their ionization energy observations:

    <p>Element X = 2 valence electrons Element Y = 4 valence electrons Element Z = 3 valence electrons</p> Signup and view all the answers

    Copper can displace Magnesium in a displacement reaction.

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

    What does oxidation refer to in a chemical reaction?

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

    In a reaction, Magnesium displaces copper from copper (II) sulfate solution, which is represented as Mg(s) + CuSO4(aq) → Cu(s) + __________(aq).

    <p>MgSO4</p> Signup and view all the answers

    Match the following metals with their level of reactivity:

    <p>Magnesium = High reactivity Copper = Low reactivity Iron = Medium reactivity Aluminum = Medium to High reactivity</p> Signup and view all the answers

    What happens to the blue color of copper (II) sulfate during its reaction with magnesium?

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

    Reduction is the gain of oxygen by a substance.

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

    What is the product formed when magnesium reacts with oxygen?

    <p>Magnesium oxide</p> Signup and view all the answers

    What happens to electronegativity as you move down a group in the periodic table?

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

    Cations are larger than their respective atoms.

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

    What is the primary difference between melting point and boiling point?

    <p>Melting point is the energy needed to change a solid to a liquid, while boiling point is the energy needed to change a liquid to a gas.</p> Signup and view all the answers

    Anions are larger than their respective atoms due to electron-electron _______.

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

    Match the type of ion with its general property:

    <p>Cation = Smaller than its respective atom Anion = Larger than its respective atom Electronegativity = Increases across a period Reactivity = Depends on the tendency to lose electrons</p> Signup and view all the answers

    Which of the following statements about the reactivity series is true?

    <p>More reactive metals tend to lose electrons</p> Signup and view all the answers

    Observations of how elements react with water and acids help form the reactivity series.

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

    What is a mnemonic device used to remember the reactivity series of metals?

    <p>People Say Little Children Make A Zebra Ill Constantly Sniffing Giraffes.</p> Signup and view all the answers

    Study Notes

    Oxidation Numbers

    • Oxidation numbers represent the charge an atom would have if electrons were transferred completely in bonds.
    • Oxidation numbers help track electron movement during chemical reactions, especially in redox reactions.

    Key Rules for Assigning Oxidation Numbers

    • The oxidation number of an element in its pure form (e.g., O₂, N₂, H₂) is 0.
    • For monoatomic ions, the oxidation number equals the ion's charge (e.g., Na⁺ = +1, Cl⁻ = -1).
    • Oxygen has an oxidation number of -2, except in peroxides (-1).
    • Hydrogen is +1 when bonded to non-metals and -1 when bonded to metals.
    • The sum of oxidation numbers in a neutral compound is 0, and in polyatomic ions, it equals the ion's charge.

    Example: Assigning Oxidation Numbers (H₂SO₄)

    • In H₂SO₄ (Sulfuric Acid):
      • Hydrogen (H) = +1 (Rule for hydrogen)
      • Oxygen (O) = -2 (Rule for oxygen)
      • Let sulfur (S) be x.
    • The sum of oxidation numbers must be 0:
      • 2(+1) + x + 4(-2) = 0
      • 2 + x - 8 = 0 → x = +6
    • Oxidation number of sulfur (S) = +6

    What is Oxidation and Reduction?

    • Oxidation: Loss of electrons or an increase in oxidation number.
    • Reduction: Gain of electrons or a decrease in oxidation number.
    • The element undergoing oxidation is the reducing agent.
    • The element undergoing reduction is the oxidizing agent.
    • In a redox reaction, one species is oxidized (loses electrons) while another is reduced (gains electrons).

    Example: Identifying Oxidation and Reduction (Zn + CuSO₄)

    • In the reaction: Zn + CuSO₄ → ZnSO₄ + Cu
      • Zn is oxidized: Zn → Zn²⁺ + 2e⁻ (Oxidation, because Zn loses electrons).
      • Cu²⁺ is reduced: Cu²⁺ + 2e⁻ → Cu (Reduction, because Cu²⁺ gains electrons).
    • Zn undergoes oxidation and Cu²⁺ undergoes reduction.

    Tips for Identifying Oxidation and Reduction

    • If the oxidation number of an element increases, it is oxidized.
    • If the oxidation number decreases, it is reduced.
    • Use the rules for assigning oxidation numbers to determine changes in a reaction.
    • Redox reactions always involve both oxidation and reduction happening together.

    Representing Chemical Reactions

    • Chemists use statements called equations to represent chemical reactions.
    • Reactants are the starting substances.
    • Products are the substances formed in the reaction.

    Word Equations

    • A word equation describes chemical change using the names of the reactants and products.
    • Example:
      • Methane + oxygen → carbon dioxide +water

    Skeleton Equations

    • A skeleton equation uses chemical formulas rather than words to identify the reactants and products.
    • Example:
      • Fe(s) + Cl₂(g) → FeCl₃(s)
      • C(s) + S(s) → CS₂

    Balanced Equation vs Skeleton Equation

    • Balanced equation: Gives the actual number of each reactant reacted with each other and the number of product molecules formed
    • Balanced equation: Gives details about reactants, products, the ratios between them, and the direction of the reaction
    • Skeleton equation: Gives the types of reactants involved in the chemical reaction and the end products
    • Skeleton equation: Gives details about reactants, products, and the direction of the reaction

    Balancing Chemical Equations

    • Balancing chemical equations can be done using four basic steps.
    • STEP 1: Write an unbalanced equation, using the correct formulas for all reactants and products.
    • STEP 2: Add appropriate coefficients to balance the numbers of atoms of each element.

    Roles of Balancing Chemical Equations

    • Chemical reactions are like recipes.
    • Balancing chemical reactions allows us to determine stoichiometry calculations by understanding the ratio between reactants and products.
    • Only add coefficients when balancing chemical equations.

    Why do we need to balance a chemical equation?

    • Sometimes, a written equation does not have an equal number of reactants and products.
    • For every chemical reaction, the law of conservation of mass must be followed.
    • The law of conservation of mass states that atoms cannot be created or destroyed.

    Writing Formulas for Ionic Compounds

    • Write the formula for the cation and anion found in the compound, considering the charge of each ion.
    • If the charges are equal, they cancel each other out directly, and we can write the formula of the compound.
    • Example: Magnesium oxide (MgO)

    Writing Formulas for Ionic Compounds -Different Charges

    • If the charges of the ionic compounds are different, crisscross the charges to identify the combining ratios.
    • Always write the cation first, then the anion, and never show the charges as part of the chemical formula.

    Common Polyatomic Ions

    • Memorize the list of polyatomic ions to write formulas of compounds containing polyatomic ions.
    • Example: Nitrate (NO₃⁻), sulfate (SO₄²⁻)

    What is a Chemical Reaction?

    • The change of one or more substances into other substances having different compositions and properties is a chemical reaction.
    • Example: C(s) + O₂(g) → CO₂(g), 2H₂(g) + O₂(g) → 2H₂O(g).
    • Reactants are the substances that react together, and products are the new substances formed.

    Types of Chemical Reactions

    • Combination reactions
    • Decomposition reactions
    • Single-replacement reactions
    • Double-replacement reactions
    • Combustion reactions

    Synthesis

    • Two or more substances react to form a single new substance (A + B → AB).
    • Examples:
      • Synthesis of two elements (C + O₂ → CO₂)
      • Synthesis of two compounds (2CaO + 2H₂O → 2Ca(OH)₂)

    Decomposition Reaction

    • A compound breaks down into elements or simpler compounds (1 Reactant → Product + Product).
    • Examples:
      • 2H₂O → 2H₂ + O₂
      • 2HgO → 2Hg + O₂

    Combustion Reactions

    • A chemical reaction where an element or compound reacts with oxygen, often producing heat and light.
    • Examples:
      • CH₄ + 2O₂ → CO₂ + 2H₂O + heat + light
      • 2Mg(s) + O₂(g) → 2MgO(s)

    Classifying Chemical Reactions (Practice Problems)

    • Classify chemical reactions into possible categories

    Writing Formulas for Ionic Compounds (Practice Problems)

    • Practice writing chemical formulas for ionic compounds including polyatomic ions

    Replacement Reactions

    • A simple replacement reaction is a chemical change in which one element replaces a second element in a compound.
    • All single replacement reactions have the general form A + BC → B + AC.

    Single Replacement Reactions (Examples and Practice)

    • Metal replaces another metal or hydrogen.
    • Check reactivity series to determine if a reaction will occur.

    Double Replacement Reactions (Guidelines)

    • Follow the guidelines to write the formulas for the products and balance the equations (cations switch places with anions)

    Practice Problems (Various Topics)

    • Solve various practice problems related to the covered topics

    Organizing Elements by Electron Configuration - Review

    • The periodic table has four blocks (s, p, d, and f).
    • Elements within a group have similar chemical properties.
    • The group number (for groups 1 and 2) equals the element's number of valence electrons.
    • The energy level of an atom's valence electrons equals its period number.
    • Atomic Radius:
      • Atomic radius decrease across a period.
      • Atomic radius increase down a group.
    • Ionization Energy:
      • Ionization energy tend to increase across a period and decrease down a group.
    • Electronegativity:
      • Electronegativity increase across a period.
      • Electronegativity decrease down a group.
    • Ionic Radius:
      • Cations are smaller than their respective atoms.
      • Anions are larger than their respective atoms.
    • Melting and Boiling Points:
      • Melting and boiling points generally decrease as it goes down the group.

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