Oxidation-reduction Reactions 5/17/11

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Questions and Answers
  • 1. 

    What was the original meaning of the term oxidation?  

    • A.

      Oxidation originally meant the combination of an element with oxygen to produce oxides.

    • B.

      Oxidation originally meant the combination of an compound with oxygen to produce oxides

    • C.

      Oxidation originally meant the combination of an element with oxygen to produce water.

    Correct Answer
    A. Oxidation originally meant the combination of an element with oxygen to produce oxides.
    Explanation
    The original meaning of the term oxidation was the combination of an element with oxygen to produce oxides. This process involves the transfer of electrons from the element to oxygen, resulting in the formation of an oxide compound. This definition is widely accepted in the field of chemistry and is still used today to describe the process of oxidation.

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  • 2. 

    Gasoline, wood, coal, and natural gas (methane) can all burn in air, producing oxides of carbon.  Bleaching is an example of oxidation.  Rusting is an example of oxidation. 

    • A.

      True about Aluminum oxide

    • B.

      True about hydrogen

    • C.

      True about oxidation

    Correct Answer
    C. True about oxidation
    Explanation
    Oxidation is a chemical reaction in which a substance combines with oxygen. It is a process that involves the loss of electrons or an increase in oxidation state. In the given statements, it is mentioned that bleaching and rusting are examples of oxidation. This indicates that both bleaching and rusting involve a substance combining with oxygen or undergoing a chemical reaction that results in the loss of electrons or an increase in oxidation state. Therefore, it can be concluded that the statement "True about oxidation" is correct.

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  • 3. 

    CH4(g)2O2(g) JKL CO2(g) 2H2O(g)  

    • A.

      Iron atoms slowly combine with oxygen in moist air to produce compounds such as iron(III) oxide.

    • B.

      Methane and oxygen are combining to produce carbon dioxide and water vapor and a great deal of heat.

    • C.

      When iron oxide is reduced to metallic iron, it gains oxygen.

    Correct Answer
    B. Methane and oxygen are combining to produce carbon dioxide and water vapor and a great deal of heat.
  • 4. 

    4Fe(s) 3O2(g) JKL 2Fe2O3(s)  

    • A.

      Iron atoms slowly combine with oxygen in moist air to produce compounds such as iron(III) oxide.

    • B.

      When iron oxide is reduced to metallic iron, it gains oxygen.

    • C.

      Iron atoms slowly combine with oxygen in moist air to produce compounds such as iron(III) oxide.

    Correct Answer
    C. Iron atoms slowly combine with oxygen in moist air to produce compounds such as iron(III) oxide.
    Explanation
    Iron atoms slowly combine with oxygen in moist air to produce compounds such as iron(III) oxide. This statement explains the process of oxidation of iron in the presence of oxygen and moisture in the air. Over time, iron atoms react with oxygen to form iron(III) oxide, which is a compound commonly known as rust. This process is a slow one and occurs gradually, leading to the formation of the reddish-brown rust on the surface of iron objects exposed to air and moisture.

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  • 5. 

    What is the name of the process that is the opposite of oxidation? 

    • A.

      Same

    • B.

      Increase

    • C.

      Reduction

    Correct Answer
    C. Reduction
    Explanation
    Reduction is the name of the process that is the opposite of oxidation. In oxidation, a substance loses electrons, while in reduction, a substance gains electrons. This process involves the addition of electrons to a molecule or atom, resulting in a decrease in its oxidation state. Reduction reactions are often coupled with oxidation reactions and together they form redox reactions.

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  • 6. 

    Oxidation never occurs without reduction and reduction never occurs without oxidation.  Oxidation–reduction reactions are also known as redox reactions.    You need to add heat in order to reduce iron ore to produce metallic iron. 

    • A.

      True about oxidation and reduction.

    • B.

      True about electrons in redox reactions.

    • C.

      True about the rate of corrosion.

    Correct Answer
    A. True about oxidation and reduction.
    Explanation
    In redox reactions, oxidation and reduction always occur together. Oxidation involves the loss of electrons, while reduction involves the gain of electrons. These reactions cannot occur independently of each other. Therefore, it is true that oxidation and reduction always happen together.

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  • 7. 

    What substance is heated along with iron ore in order to reduce the metal oxide to metallic iron? 

    • A.

      Charcoal (carbon)

    • B.

      Redox reaction

    • C.

      Covalent compounds

    Correct Answer
    A. Charcoal (carbon)
    Explanation
    Charcoal (carbon) is heated along with iron ore to reduce the metal oxide to metallic iron. Carbon acts as a reducing agent in this process by combining with the oxygen present in the metal oxide, forming carbon dioxide. This reaction, known as a redox reaction, involves the transfer of electrons from the carbon to the metal oxide, resulting in the reduction of the metal oxide to metallic iron. Covalent compounds are not directly involved in this process.

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  • 8. 

    What do the iron artifacts tell you about what chemistry early Iron Age people knew 2500 years ago? 

    • A.

      Early Iron Age people knew how to keep the same amount of iron ore to metallic iron by heating the ore with charcoal.

    • B.

      Early Iron Age people knew how to increase iron ore to metallic iron by heating the ore with charcoal.

    • C.

      Early Iron Age people knew how to reduce iron ore to metallic iron by heating the ore with charcoal.

    Correct Answer
    C. Early Iron Age people knew how to reduce iron ore to metallic iron by heating the ore with charcoal.
    Explanation
    The correct answer indicates that the iron artifacts suggest that early Iron Age people knew how to reduce iron ore to metallic iron by heating it with charcoal. This implies that they had knowledge of the chemical process of reducing iron ore to obtain iron.

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  • 9. 

    When iron ore is reduced to metallic iron, what oxidation reaction occurs at the same time?  time?   

    • A.

      Carbon combines with oxygen from the iron(III) oxide to form carbon zioxide.

    • B.

      Carbon combines with oxygen from the iron(III) oxide to form carbon monoxide.

    • C.

      Carbon combines with oxygen from the iron(III) oxide to form carbon dioxide.

    Correct Answer
    C. Carbon combines with oxygen from the iron(III) oxide to form carbon dioxide.
    Explanation
    When iron ore is reduced to metallic iron, the oxidation reaction that occurs at the same time is that carbon combines with oxygen from the iron(III) oxide to form carbon dioxide.

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  • 10. 

    What do the iron artifacts tell you about what chemistry early Iron Age people knew 2500 years ago? 

    • A.

      Early Iron Age people knew how to reduce iron ore to metallic iron by heating the ore with charcoal.

    • B.

      Early Iron Age people knew how to increase iron ore to metallic iron by heating the ore with charcoal.

    • C.

      Early Iron Age people knew how to keep the same iron ore to metallic iron by heating the ore with charcoal.

    Correct Answer
    A. Early Iron Age people knew how to reduce iron ore to metallic iron by heating the ore with charcoal.
    Explanation
    The correct answer suggests that early Iron Age people had knowledge of the process of reducing iron ore to metallic iron by heating it with charcoal. This implies that they were familiar with the chemical reactions involved in this process and had the necessary understanding of chemistry to carry out such a procedure.

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  • 11. 

    When iron ore is reduced to metallic iron, what oxidation reaction occurs at the same time?  time?   

    • A.

      Carbon combines with oxygen from the coal(III) oxide to form carbon dioxide.

    • B.

      Carbon combines with oxygen from the iron(III) oxide to form carbon dioxide.

    • C.

      Carbon combines with oxygen from the lead(III) oxide to form carbon dioxide.

    Correct Answer
    B. Carbon combines with oxygen from the iron(III) oxide to form carbon dioxide.
    Explanation
    When iron ore is reduced to metallic iron, the oxidation reaction that occurs at the same time is carbon combining with oxygen from the iron(III) oxide to form carbon dioxide.

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  • 12. 

    The concepts of oxidation and reduction have been extended to include many reactions that do not even involve _______________.  involve oxygen.   

    • A.

      Water

    • B.

      Oxygen

    • C.

      Iron

    Correct Answer
    B. Oxygen
    Explanation
    The concepts of oxidation and reduction have been extended to include many reactions that do not even involve oxygen. This means that oxidation and reduction can occur without the presence of oxygen. Oxygen is not necessary for a reaction to be classified as an oxidation or reduction reaction.

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  • 13. 

    What is understood about electrons in redox reactions? 

    • A.

      Redox reactions involve a shift of nuetrons between reactants.

    • B.

      Redox reactions involve a shift of protons between reactants.

    • C.

      Redox reactions involve a shift of electrons between reactants.

    Correct Answer
    C. Redox reactions involve a shift of electrons between reactants.
    Explanation
    In redox reactions, there is a transfer or shift of electrons between the reactants. This transfer of electrons is what drives the chemical reaction and allows for the formation of new products. The reactant that loses electrons is oxidized, while the reactant that gains electrons is reduced. This transfer of electrons is essential for the transfer of energy and the conversion of chemical species.

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  • 14. 

    When magnesium and sulfur are heated together, they undergo a ______________reaction to form magnesium sulfide. 

    • A.

      Redox

    • B.

      Reflox

    • C.

      Remox

    Correct Answer
    A. Redox
    Explanation
    When magnesium and sulfur are heated together, they undergo a redox reaction to form magnesium sulfide. In a redox reaction, there is a transfer of electrons between the reactants. In this case, magnesium loses electrons to form positively charged magnesium ions, while sulfur gains electrons to form negatively charged sulfide ions. This transfer of electrons indicates a change in oxidation states, hence the term "redox" (reduction-oxidation) reaction.

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  • 15. 

    ________________ are transferred from the metal atoms to the nonmetal atoms in this reaction. 

    • A.

      Protons

    • B.

      Nuetrons

    • C.

      Electrons

    Correct Answer
    C. Electrons
    Explanation
    In this reaction, electrons are transferred from the metal atoms to the nonmetal atoms. Electrons are negatively charged particles that orbit the nucleus of an atom. When a metal and a nonmetal react, the metal atom loses electrons and becomes positively charged, while the nonmetal atom gains electrons and becomes negatively charged. This transfer of electrons allows the atoms to achieve a stable electron configuration and form an ionic bond.

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  • 16. 

    A redox reaction may produce covalent _____________________. 

    • A.

      Mixtures

    • B.

      Compounds

    • C.

      Substances

    Correct Answer
    B. Compounds
    Explanation
    A redox reaction involves the transfer of electrons between species. During this process, new chemical bonds can form between atoms, resulting in the production of compounds. Compounds are formed when two or more elements chemically combine and share electrons to achieve a stable configuration. Therefore, it is likely that a redox reaction can produce covalent compounds as a result of the electron transfer and bond formation.

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  • 17. 

    Preventing and repairing damage from corrosion of metals requires _____________ of dollars every year. 

    • A.

      Billions

    • B.

      Millions

    • C.

      Trillions

    Correct Answer
    A. Billions
    Explanation
    Preventing and repairing damage from corrosion of metals requires a significant amount of money every year. The correct answer is "billions" because corrosion is a widespread problem that affects various industries and infrastructure. The cost of corrosion includes expenses for maintenance, repairs, and replacement of corroded metal structures and equipment. Given the scale of the problem and the economic impact of corrosion, it is reasonable to assume that billions of dollars are spent annually to combat and mitigate its effects.

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  • 18. 

    Iron corrodes by being oxidized to ions of iron by _________________. 

    • A.

      Oxygen

    • B.

      Hydrogen

    • C.

      Carbon dioxide

    Correct Answer
    A. Oxygen
    Explanation
    Iron corrodes by being oxidized to ions of iron by oxygen. When iron comes into contact with oxygen in the presence of moisture, a chemical reaction occurs that results in the formation of iron oxide, commonly known as rust. This process is known as oxidation, where oxygen acts as the oxidizing agent, causing the iron to lose electrons and form iron ions. The iron ions then combine with water and oxygen to form hydrated iron oxide, which is the reddish-brown rust that we commonly associate with the corrosion of iron.

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  • 19. 

    The presence of salts and acids increases the rate of corrosion by producing conducting solutions that make the transfer of _____________ easier. 

    • A.

      Nuetrons

    • B.

      Protons

    • C.

      Electrons

    Correct Answer
    C. Electrons
    Explanation
    The presence of salts and acids increases the rate of corrosion by producing conducting solutions that make the transfer of electrons easier. Salts and acids can dissociate into ions in water, creating a conductive medium. This allows for the movement of charged particles, specifically electrons, which are responsible for the process of corrosion. Therefore, the presence of salts and acids enhances the ability of electrons to move and facilitates the corrosion process.

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  • 20. 

    Why are gold and platinum called noble metals? 

    • A.

      Because gold and platinum are very resistant to gaining their electrons through corrosion

    • B.

      Because gold and platinum are very resistant to losing their electrons through corrosion

    • C.

      Because gold and platinum are very resistant to keeping their electrons through corrosion

    Correct Answer
    B. Because gold and platinum are very resistant to losing their electrons through corrosion
    Explanation
    Gold and platinum are called noble metals because they are very resistant to losing their electrons through corrosion. This means that they do not easily react with other elements or substances, making them highly unreactive and stable. This property makes them valuable for various applications, including jewelry and industrial uses, as they do not tarnish or corrode easily.

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  • 21. 

    Explain how differences between the oxides affect further corrosion of the metals.  oxides affect further corrosion of the metals.   

    • A.

      Aluminum oxide forms a tightly packed protective layer that does not admit water. Because iron(III) oxide is not tightly packed, it allows water to penetrate and attack the metal below.

    • B.

      Sodium oxide forms a tightly packed protective layer that does not admit water. Because iron(III) oxide is not tightly packed, it allows water to penetrate and attack the metal below.

    • C.

      Patrolium oxide forms a tightly packed protective layer that does not admit water. Because iron(III) oxide is not tightly packed, it allows water to penetrate and attack the metal below.

    Correct Answer
    A. Aluminum oxide forms a tightly packed protective layer that does not admit water. Because iron(III) oxide is not tightly packed, it allows water to penetrate and attack the metal below.
    Explanation
    The differences between the oxides affect further corrosion of the metals because aluminum oxide forms a tightly packed protective layer that does not allow water to penetrate, thus preventing further corrosion. On the other hand, iron(III) oxide is not tightly packed, allowing water to penetrate and attack the metal below, leading to further corrosion. Therefore, the presence of a tightly packed protective layer determines the extent of corrosion in metals.

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  • 22. 

    As a general rule, a bonded atom’s oxidation number is the charge that it would have if the electrons in the bond were assigned to the more ___________________element. ..

    • A.

      electropositive

    • B.

      electronegative

    • C.

      electronuetral

    Correct Answer
    B. electronegative
    Explanation
    The correct answer is electronegative. According to the general rule stated in the question, the oxidation number of a bonded atom is determined by assigning the electrons in the bond to the more electronegative element. This means that the electronegative element has a higher tendency to attract electrons towards itself, resulting in a partial negative charge and a higher oxidation number.

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  • 23. 

    Even though water is a molecular compound, you can still obtain oxidation numbers for the bonded elements by pretending that the electrons contributed by the __________________atoms are completely transferred to oxygen. 

    • A.

      Oxygen

    • B.

      Water

    • C.

      Hydrogen

    Correct Answer
    C. Hydrogen
    Explanation
    Even though water is a molecular compound, you can still obtain oxidation numbers for the bonded elements by pretending that the electrons contributed by the hydrogen atoms are completely transferred to oxygen. This means that each hydrogen atom is assigned an oxidation number of +1, while oxygen is assigned an oxidation number of -2. This allows for the calculation of the overall oxidation state of the water molecule.

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  • 24. 

    Write the oxidation number, or the sum of the oxidation numbers, for the given atoms, ions, or compounds.  __________   Cu(II) ion 

    • A.

      -1

    • B.

      -2

    • C.

      +2

    Correct Answer
    C. +2
    Explanation
    The oxidation number of the Cu(II) ion is +2. This is because copper (Cu) typically has a +2 oxidation state when it forms an ion. The Roman numeral "II" in Cu(II) indicates that the copper ion has a +2 charge.

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  • 25. 

    Write the oxidation number, or the sum of the oxidation numbers, for the given atoms, ions, or compounds.   _______Hydrogen in water 

    • A.

      +2

    • B.

      +1

    • C.

      -1

    Correct Answer
    B. +1
    Explanation
    In water, the oxidation number of hydrogen is +1. This is because hydrogen is less electronegative than oxygen, so it tends to lose electrons and have a positive oxidation number. In the case of water, each hydrogen atom is bonded to an oxygen atom, which is more electronegative. Oxygen has an oxidation number of -2, and since the overall charge of water is neutral, the oxidation number of hydrogen must be +1 to balance out the -2 charge of oxygen.

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  • 26. 

    ___________Hydrogen in sodium hydride (NaH) 

    • A.

      +1

    • B.

      0

    • C.

      -1

    Correct Answer
    C. -1
    Explanation
    In sodium hydride (NaH), hydrogen has a charge of -1. This is because sodium is a group 1 element with a charge of +1, and in order for the compound to be neutral, hydrogen must have a charge of -1 to balance out the positive charge of sodium.

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  • 27. 

    ___________Potassium sulfate (K2SO4)  

    • A.

      0

    • B.

      1

    • C.

      2

    Correct Answer
    A. 0
  • 28. 

    Label each change O if it describes oxidation or R if it describes reduction N if neither. Decrease in the oxidation number of an element   

    • A.

      O

    • B.

      R

    • C.

      N

    Correct Answer
    B. R
    Explanation
    The given correct answer is "R" because a decrease in the oxidation number of an element indicates reduction. Reduction is the gain of electrons or a decrease in oxidation state.

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  • 29. 

    Label each change O if it describes oxidation or R if it describes reduction N if neither. Increase in the oxidation number of an element   

    • A.

      O

    • B.

      R

    • C.

      N

    Correct Answer
    A. O
    Explanation
    An increase in the oxidation number of an element indicates that the element has undergone oxidation. This means that the element has lost electrons and has become more positively charged. Therefore, the correct answer is O, which stands for oxidation.

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  • 30. 

    Name two kinds of reactions that are not redox reactions. 

    • A.

      Two-replacement reactions and acid–base reactions are not redox reactions.

    • B.

      Triple-replacement reactions and acid–base reactions are not redox reactions.

    • C.

      Double-replacement reactions and acid–base reactions are not redox reactions.

    Correct Answer
    C. Double-replacement reactions and acid–base reactions are not redox reactions.
    Explanation
    Double-replacement reactions and acid-base reactions are not redox reactions because they do not involve a transfer of electrons between reactants. In a double-replacement reaction, ions from two different compounds exchange places, but there is no change in the oxidation states of the elements involved. In an acid-base reaction, a proton is transferred from an acid to a base, but again, there is no change in oxidation states. Redox reactions, on the other hand, involve a transfer of electrons and a change in oxidation states.

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  • 31. 

    When a solution changes color during a reaction, what can you concludeabout the reaction that has taken place?  about the reaction that has taken place?   

    • A.

      The reaction is a redox reaction.

    • B.

      Decrease in the oxidation number of an element

    • C.

      Electrons contributed by the hydrogen atoms

    Correct Answer
    A. The reaction is a redox reaction.
    Explanation
    When a solution changes color during a reaction, it indicates that electrons have been transferred between the reactants. This suggests that the reaction is a redox (reduction-oxidation) reaction, where there is a decrease in the oxidation number of an element and electrons are contributed by the hydrogen atoms.

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  • 32. 

    Answer these questions to help you balance the following equation using the oxidation-number-change method. H2(g)O2(g) _____> H2O(l) (unbalanced) What are the oxidation numbers for each atom in the equation?   

    • A.

      0 0 +1-2 H3(g) + O2(g) ____> H3O

    • B.

      0 0 +1-2 H2(g) + O2(g) ____> H2O

    • C.

      0 0 +1-2 H3(g) + O2(g) ____> H2O

    Correct Answer
    B. 0 0 +1-2 H2(g) + O2(g) ____> H2O
    Explanation
    In this equation, the oxidation number of hydrogen (H) is 0 and the oxidation number of oxygen (O) is -2 in both H2(g) and O2(g). In H2O(l), the oxidation number of hydrogen (H) is +1 and the oxidation number of oxygen (O) is -2. Therefore, in order to balance the equation, two hydrogen atoms from H2(g) must combine with one oxygen atom from O2(g) to form H2O(l).

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  • 33. 

    Answer these questions to help you balance the following equation using the oxidation-number-change method. H2(g)O2(g) _____>H2O(l) (unbalanced) Which element is oxidized in this reaction? Which is reduced?   

    • A.

      Nothing is oxidized; nothing is reduced.

    • B.

      Oxygen is oxidized;hydrogen is reduced.

    • C.

      Hydrogen is oxidized; oxygen is reduced.

    Correct Answer
    C. Hydrogen is oxidized; oxygen is reduced.
    Explanation
    In this reaction, hydrogen is oxidized and oxygen is reduced. This is because the oxidation number of hydrogen in H2 is 0, and in H2O it is +1. Therefore, hydrogen has undergone oxidation. On the other hand, the oxidation number of oxygen in O2 is 0, and in H2O it is -2. Therefore, oxygen has undergone reduction.

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  • 34. 

    The equations for which reactions are balanced separately when using the half-reaction method? 

    • A.

      The oxidation and reduction equations are balanced separately.

    • B.

      The oxidation and reduction equations are balanced together.

    • C.

      The oxidation and reduction equations are not balanced.

    Correct Answer
    A. The oxidation and reduction equations are balanced separately.
    Explanation
    When using the half-reaction method, the oxidation and reduction reactions are balanced separately. This is because the half-reaction method breaks down the overall reaction into two separate half-reactions: one for the oxidation reaction and one for the reduction reaction. Each half-reaction is balanced individually by adding the appropriate number of electrons and balancing the atoms and charges. Once both half-reactions are balanced, they can be combined to form the balanced overall reaction.

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  • 35. 

    For what kind of reaction is the half-reaction method particularly useful? 

    • A.

      Electron reactions in solution

    • B.

      Ionic reactions in solution

    • C.

      Proton reactions in solution

    Correct Answer
    B. Ionic reactions in solution
    Explanation
    The half-reaction method is particularly useful for ionic reactions in solution. This method involves splitting the overall reaction into two half-reactions, one representing the oxidation process and the other representing the reduction process. By doing so, it becomes easier to balance the equation and determine the transfer of electrons between species. In ionic reactions, the transfer of electrons is a key factor, and the half-reaction method allows for a clearer understanding and analysis of these electron transfers.

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  • Mar 21, 2023
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