Question 1

Consider the following unbalanced half-reaction: MnO₄⁻ → MnO₂.The oxidation number of Mn changes from ________,and the Mn is ________.

Accepted Answer

The oxidation number of Mn in MnO₄⁻ is +7, and in MnO₂ it is +4. The decrease in oxidation number indicates that Mn is reduced.

Question 2

In which of the following is the reactant undergoing oxidation? (Note: These reactions are not complete chemical equations.)

Accepted Answer

In option D, the reactant (C) is being oxidized to form CO₂. This can be seen because the oxidation state of carbon in C is 0, whereas in CO₂ it is +4. In all the other options, the reactants are being reduced, not oxidized.

Question 3

Every reduction reaction MUST be accompanied by

Accepted Answer

In any redox reaction, one species loses electrons (oxidation) and another gains electrons (reduction). Therefore, every reduction reaction must be accompanied by an oxidation reaction which involves the opposite electron transfer.

Question 4

The black,granular material that fills a dry cell in a common flashlight (between the carbon rod and the zinc shell)is manganese(II)oxide,MnO₂.The oxidation number of manganese in MnO₂ is

Accepted Answer

The oxidation number of oxygen is -2 and there are two oxygen atoms in MnO₂, giving a total oxidation number of -4. The overall charge of the compound is 0, so the oxidation number of manganese (Mn) must be +4 to balance out the negative charge from the two oxygen atoms. Therefore, the correct answer is C.

Question 5

Consider the following unbalanced equation between copper(I)ions and iron to produce copper metal and iron(II)ions: Cu⁺ + Fe → Cu + Fe²⁺ What is oxidized in this reaction?

Accepted Answer

In the given reaction, iron is being oxidized as it goes from a zero oxidation state to a +2 oxidation state (Fe → Fe²⁺).

Question 6

Sodium bisulfite converts bromine (Br₂)to bromide (Br⁻).Sodium bisulfite is a(n)

Accepted Answer

Sodium bisulfite is a reducing agent, as it causes the bromine to gain electrons and become bromide.

Question 7

In the reaction Cu⁺ + Fe → Cu + Fe²⁺ (Note: The reaction is not balanced.)

Accepted Answer

In the given reaction, Fe undergoes oxidation and loses electrons to become Fe²⁺. Therefore, Fe is the species that is being oxidized and is the reducing agent.

Question 8

What is the oxidation number of bismuth in Bi₂O₃?

Accepted Answer

In Bi₂O₃, the overall charge of oxide (O) is -6 (as it has a charge of -2 per oxygen atom) and since the compound is neutral, the overall charge of bismuth (Bi) must be +6 to balance out the negative charge of oxygen atoms. The oxidation number of oxygen atoms in oxide compounds is always -2, and since there are three oxygen atoms in Bi2O3, the total negative charge on oxygen atoms is -6. Therefore, the oxidation number of Bi is +6.

Question 9

In which of the following partial reactions is the reactant undergoing reduction? (Note: The reactions are not complete.)

Accepted Answer

PbO is reduced to Pb, as oxygen is removed from the molecule.

Question 10

The oxidation number of F⁻¹ is

Accepted Answer

Fluorine has an oxidation number of -1 in F⁻¹ because it has gained one electron.

Question 11

Which substance is an oxidizing agent?

Accepted Answer

H₂O₂ is a well-known oxidizing agent because it releases oxygen when it decomposes. This process is called oxidation. NaOH, HI, and LiBr are not oxidizing agents. NaOH is a strong base and is used as a cleaning agent. HI is a reducing agent because it can donate iodide ions (I-) to another substance. LiBr is a salt and has no oxidizing or reducing power.

Question 12

When C₃H₈ is burned in oxygen,the products are

Accepted Answer

When C₃H₈ is burned in oxygen, it undergoes combustion reactions where the reactants react with oxygen to form products. The balanced equation for the combustion of C₃H₈ is:

C₃H₈ + 5O₂ → 3CO₂ + 4H₂O

This means that the products formed are carbon dioxide (CO₂) and water (H₂O). Therefore, the best choice is option D, which states CO₂ + H₂O as the products formed.

Question 13

Which of the following is a definition of oxidation?

Accepted Answer

Oxidation is defined as the loss of electrons. In a chemical reaction, when an atom, ion, or molecule loses one or more electrons, it is said to undergo oxidation. This results in an increase in the oxidation state of the species that lost electrons.

Question 14

What is reduced in the following reaction?
2 Bi³⁺ + 3 Mg → 2 Bi + 3 Mg²⁺

Accepted Answer

Bi³⁺ undergoes reduction by gaining electrons and being converted to Bi, while Mg undergoes oxidation by losing electrons and being converted to Mg²⁺. The substance that undergoes reduction is the one that is being reduced, in this case Bi³⁺.

Question 15

The carbon in C₂H₆O₂ is ________ in the following reaction: C₂H₆O₂ → C₂H₄O₂ + H₂

Accepted Answer

In the given reaction, the carbon in C₂H₆O₂ is converted into C₂H₄O₂ by losing two hydrogen atoms. This means that carbon has lost electrons and has undergone oxidation. Therefore, the correct choice is A) oxidized.

Question 16

All redox reactions occur with the transfer of

Accepted Answer

Redox reactions involve the transfer of electrons between species. Therefore, the best choice is B, electrons. A (protons) is not always transferred in redox reactions, and C (chlorine) and D (nitrogen) are not always involved in redox reactions.

Question 17

Which of the following is a definition of reduction?

Accepted Answer

Reduction is defined as the gain of electrons, which may be accompanied by the gain of hydrogen atoms or the loss of oxygen atoms. Therefore, option B, which states that reduction is the gain of hydrogen, is the most accurate definition from the given options.

Question 18

The oxidation number for l in l₂ is

Accepted Answer

In diatomic iodine (I₂), each iodine atom has an oxidation number of 0 because it is in its elemental form.

Question 19

In which of the following is the reactant undergoing reduction? (Note: These reactions are not complete chemical equations.)

Accepted Answer

In reaction B, C₂H₄O is being reduced to C₂H₆O by gaining two hydrogen atoms. Reduction involves gaining electrons or gaining hydrogen atoms, whereas oxidation involves loss of electrons or loss of hydrogen atoms. None of the other reactions in the given options involve reduction.

Question 20

With respect to energy content,reduced forms of matter are generally

Accepted Answer

Reduced forms of matter, such as hydrocarbons, sugars, and fats, are high in potential energy due to the presence of chemical bonds that can be broken to release energy. This is why they often make good fuels for living organisms and for human use.

Quiz 8: Oxidation and Reduction

Consider the following unbalanced half-reaction: MnO₄⁻ → MnO₂.The oxidation number of Mn changes from ,and the Mn is .