Question 1

________ is the reducing agent in the reaction below. Cr₂O₇^2- + 6S₂O₃^2- + 14H⁺ → 2Cr³⁺ + 3S₄O₆^2- + 7H₂O

Accepted Answer

S₂O₃^2- is the reducing agent because it donates electrons, causing the reduction of Cr₂O₇^2- to Cr³⁺.

Question 2

What is the oxidation number of oxygen in K₂O₂?

Accepted Answer

The answer of What is the oxidation number of oxygen...

Question 3

Which substance is the oxidizing agent in the reaction below? Pb + PbO₂ + 2H₂SO₄ → 2PbSO₄ + 2H₂O

Accepted Answer

In the given reaction, Pb is being oxidized from its elemental form to PbO, indicating that PbO is the oxidizing agent. Therefore, the answer is D, PbO₂.

Question 4

Which element is oxidized in the following reaction? Cr₂O₇^2- + 6S₂O₃^2- + 14H⁺ → 2Cr³⁺ + 3S₄O₆^2- + 7H₂O

Accepted Answer

Sulfur (S) in S₂O₃^2- is oxidized to S₄O₆^2-, increasing its oxidation state.

Question 5

The loss of electrons by an element is called ________.

Accepted Answer

The loss of electrons by an element is called oxidation, as it involves the element losing negatively charged electrons. Reduction is the gain of electrons, disproportionation is the simultaneous oxidation and reduction of an element, fractionation is not related to electron loss/gain, and sublimation is the direct transition from solid to gas phase without passing through the liquid phase.

Question 6

________ is the reducing agent in the reaction below. Na(s)+ 2Cl₂(g)→ 2NaCl(s)

Accepted Answer

In a redox reaction, the reducing agent is the species that undergoes oxidation, i.e. loses electrons. In this reaction, the only species that can undergo oxidation is Na, which loses an electron to form Na+ in NaCl. Therefore, Na is the reducing agent. None of the other species listed are capable of losing electrons in this reaction.

Question 7

________ is the oxidizing agent in the reaction below. Na(s)+ 2Cl₂(g)→ 2NaCl(s)

Accepted Answer

The oxidizing agent is the species that gets reduced by gaining electrons. In the given reaction, Cl₂ is reduced to Cl⁻ (in NaCl), thus Cl₂ (E) is the oxidizing agent.

Question 8

In a lead-acid battery,the electrodes are consumed.In this battery,________.

Accepted Answer

In a lead-acid battery, the anode is made of lead (Pb) and is consumed during discharge as it reacts with sulfuric acid to form lead sulfate (PbSO4). Therefore, choice A is the correct answer.

Question 9

Which substance is serving as the oxidizing agent in the following reaction? CH₄(g)+ 2O₂(g)→ CO₂(g)+ 2H₂O(g)

Accepted Answer

In the reactants, oxygen is in the oxidation state of 0 while in the product, oxygen is in the oxidation state of -2 in COS12O. This means that oxygen has gained electrons, and therefore, has been reduced. The substance that causes reduction is the oxidizing agent. Therefore, the substance serving as the oxidizing agent in this reaction is OS12O.

Question 10

What is being reduced at the cathode in the hydrogen fuel cell?

Accepted Answer

At the cathode of a hydrogen fuel cell, the reduction of oxygen (O2) occurs to form water (H2O). Therefore, choice A, which represents oxygen, is the correct answer. The other options listed are not involved in the reduction process at the cathode of a hydrogen fuel cell.

Question 11

Which element is reduced in the following reaction? Cr₂O₇^2- + 6S₂O₃^2- + 14H⁺ → 2Cr³⁺ + 3S₄O₆^2- + 7H₂O

Accepted Answer

In the given reaction, chromium (Cr) goes from an oxidation state of +6 in Cr2O7^2- to an oxidation state of +3 in Cr^3+. This decrease in oxidation state indicates that chromium is reduced.

Question 12

What is the oxidation number of manganese in MnO₂?

Accepted Answer

The oxidation number of oxygen is usually -2 and sulfur is usually -2 or -1. The sum of oxidation numbers in a compound equals zero. Let x be the oxidation number of manganese. Then we can write the equation: x + (-2) + (-2) = 0 Solving for x, we get x = +4. Therefore, the oxidation number of manganese in MnO₂ is +4, which is option D.

Question 13

What is the cathode in an alkaline battery?

Accepted Answer

In an alkaline battery, the cathode is made of manganese dioxide (MnO2).

Question 14

One of the differences between a voltaic cell and an electrolytic cell is that in an electrolytic cell,________.

Accepted Answer

In an electrolytic cell, a nonspontaneous reaction is forced to occur by the application of an external electric current. In contrast, a voltaic (or galvanic) cell produces an electric current spontaneously as a result of a chemical reaction.

Question 15

What is the oxidation number of oxygen in H₂O₂?

Accepted Answer

In hydrogen peroxide (H2O2), oxygen has an oxidation number of -1 because the molecule is a peroxide, where each oxygen is bonded to another oxygen, resulting in a -1 oxidation state for each oxygen atom.

Question 16

What is the oxidation number of manganese in KMnO4?

Accepted Answer

In KMnO4, the oxidation state of oxygen is -2 since it is in its usual state, and the oxidation state of potassium is +1 since it belongs to Group 1. Thus, we can use the formula: 
(+1) + x + 4(-2) = 0, where x is the oxidation state of manganese.
Solving for x gives us +7, so the answer is C.

Question 17

Which of the statements about cathodic protection of a metal pipe against corrosion is correct?

Accepted Answer

Cathodic protection involves making the metal to be protected the cathode (negative electrode) in an electrochemical cell. This is achieved by attaching an active metal, such as magnesium or zinc, to the metal pipe. The active metal will corrode preferentially to the pipe, providing electrons to the pipe and making it the cathode. This protects the pipe from corroding by sacrificing the active metal instead.

Question 18

Which substance does not undergo oxidation or reduction in the reaction below? Pb + PbO₂ + 2H₂SO₄ → 2PbSO₄ + 2H₂O

Accepted Answer

HSO₄⁻ (B) does not undergo oxidation or reduction in the given reaction. It acts as a spectator ion, remaining unchanged from reactants to products.

Question 19

What is the oxidation number of chromium in K₂Cr₂O₇?

Accepted Answer

The oxidation number of sulfur is -2, and there are two sulfur atoms present in the compound, giving a total charge of -4. The oxidation number of oxygen is also -2, and there are 17 oxygen atoms present, giving a total charge of -34. To balance the negative charges, the oxidation number of chromium must be +6.

Question 20

What is the anode in an alkaline battery?

Accepted Answer

The anode in an alkaline battery is typically made of zinc powder. Zinc is used because it is a highly reactive metal and is capable of easily giving up electrons, which is necessary for the battery to generate electricity.

Quiz 20: Electrochemistry

________ is the reducing agent in the reaction below. Cr₂O₇^2- + 6S₂O₃^2- + 14H⁺ → 2Cr³⁺ + 3S₄O₆^2- + 7H₂O

What is the oxidation number of oxygen in K₂O₂?

Which substance is the oxidizing agent in the reaction below? Pb + PbO₂ + 2H₂SO₄ → 2PbSO₄ + 2H₂O

Which element is oxidized in the following reaction? Cr₂O₇^2- + 6S₂O₃^2- + 14H⁺ → 2Cr³⁺ + 3S₄O₆^2- + 7H₂O

The loss of electrons by an element is called ________.

________ is the reducing agent in the reaction below. Na(s) + 2Cl₂(g) → 2NaCl(s)

________ is the oxidizing agent in the reaction below. Na(s) + 2Cl₂(g) → 2NaCl(s)

In a lead-acid battery,the electrodes are consumed.In this battery,________.

Which substance is serving as the oxidizing agent in the following reaction? CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)

What is being reduced at the cathode in the hydrogen fuel cell?

Which element is reduced in the following reaction? Cr₂O₇^2- + 6S₂O₃^2- + 14H⁺ → 2Cr³⁺ + 3S₄O₆^2- + 7H₂O

What is the oxidation number of manganese in MnO₂?

What is the cathode in an alkaline battery?

One of the differences between a voltaic cell and an electrolytic cell is that in an electrolytic cell,________.

What is the oxidation number of oxygen in H₂O₂?

What is the oxidation number of manganese in KMnO4?

Which of the statements about cathodic protection of a metal pipe against corrosion is correct?

Which substance does not undergo oxidation or reduction in the reaction below? Pb + PbO₂ + 2H₂SO₄ → 2PbSO₄ + 2H₂O

What is the oxidation number of chromium in K₂Cr₂O₇?

What is the anode in an alkaline battery?

Quiz 20: Electrochemistry

________ is the reducing agent in the reaction below. Cr2O72- + 6S2O32- + 14H+ → 2Cr3+ + 3S4O62- + 7H2O

What is the oxidation number of oxygen in K2O2?

Which substance is the oxidizing agent in the reaction below? Pb + PbO2 + 2H2SO4 → 2PbSO4 + 2H2O

Which element is oxidized in the following reaction? Cr2O72- + 6S2O32- + 14H+ → 2Cr3+ + 3S4O62- + 7H2O

The loss of electrons by an element is called ________.

________ is the reducing agent in the reaction below. Na(s) + 2Cl2(g) → 2NaCl(s)

________ is the oxidizing agent in the reaction below. Na(s) + 2Cl2(g) → 2NaCl(s)

In a lead-acid battery,the electrodes are consumed.In this battery,________.

Which substance is serving as the oxidizing agent in the following reaction? CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)

What is being reduced at the cathode in the hydrogen fuel cell?

Which element is reduced in the following reaction? Cr2O72- + 6S2O32- + 14H+ → 2Cr3+ + 3S4O62- + 7H2O

What is the oxidation number of manganese in MnO2?

What is the cathode in an alkaline battery?

One of the differences between a voltaic cell and an electrolytic cell is that in an electrolytic cell,________.

What is the oxidation number of oxygen in H2O2?

What is the oxidation number of manganese in KMnO4?

Which of the statements about cathodic protection of a metal pipe against corrosion is correct?

Which substance does not undergo oxidation or reduction in the reaction below? Pb + PbO2 + 2H2SO4 → 2PbSO4 + 2H2O

What is the oxidation number of chromium in K2Cr2O7?

What is the anode in an alkaline battery?

________ is the reducing agent in the reaction below. Cr₂O₇^2- + 6S₂O₃^2- + 14H⁺ → 2Cr³⁺ + 3S₄O₆^2- + 7H₂O

What is the oxidation number of oxygen in K₂O₂?

Which substance is the oxidizing agent in the reaction below? Pb + PbO₂ + 2H₂SO₄ → 2PbSO₄ + 2H₂O

Which element is oxidized in the following reaction? Cr₂O₇^2- + 6S₂O₃^2- + 14H⁺ → 2Cr³⁺ + 3S₄O₆^2- + 7H₂O

________ is the reducing agent in the reaction below. Na(s) + 2Cl₂(g) → 2NaCl(s)

________ is the oxidizing agent in the reaction below. Na(s) + 2Cl₂(g) → 2NaCl(s)

Which substance is serving as the oxidizing agent in the following reaction? CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)

Which element is reduced in the following reaction? Cr₂O₇^2- + 6S₂O₃^2- + 14H⁺ → 2Cr³⁺ + 3S₄O₆^2- + 7H₂O

What is the oxidation number of manganese in MnO₂?

What is the oxidation number of oxygen in H₂O₂?

Which substance does not undergo oxidation or reduction in the reaction below? Pb + PbO₂ + 2H₂SO₄ → 2PbSO₄ + 2H₂O

What is the oxidation number of chromium in K₂Cr₂O₇?