MCAT General Chemistry Review

Chapter 11: Oxidation–Reduction Reactions

Practice Questions

1. Consider the following equation:

6 Na (s) + 2 NH₃ (aq) → 2 Na₃N (s) + 3 H₂ (g)

Which species acts as an oxidizing agent?

1. Na

2. N in NH₃

3. H in NH₃

4. H₂

2. How many electrons are involved in the following half-reaction after it is balanced?

Cr₂O₇²⁻ + H⁺ + e⁻ → Cr²⁺ + H₂O

1. 2

2. 8

3. 12

4. 16

3. Lithium aluminum hydride (LiAlH₄) is often used in laboratories because of its tendency to donate a hydride ion. Which of the following roles would lithium aluminum hydride likely play in a reaction?

1. Strong reducing agent only

2. Strong oxidizing agent only

3. Both a strong reducing agent and strong oxidizing agent

4. Neither a strong reducing agent nor a strong oxidizing agent

4. What is the oxidation number of chlorine in NaClO?

1. –1

2. 0

3. +1

4. +2

5. The following electronic configurations represent elements in their neutral form. Which element is the strongest oxidizing agent?

1. 1s²2s²2p⁶3s²3p⁶4s²

2. 1s²2s²2p⁶3s²3p⁶4s²3d⁵

3. 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p¹

4. 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁵

6. Which of the following is the correct net ionic reaction for the reaction of copper with silver(I) nitrate?

1. Cu + AgNO₃ → Cu(NO₃)₂ + Ag

2. Cu + 2 Ag⁺ + NO₃⁻ → Cu²⁺ + 2 NO₃⁻ + 2 Ag⁺

3. 2 Ag⁺ + 2 NO₃⁻ → 2 NO₃⁻ + 2 Ag⁺

4. Cu + 2 Ag⁺ → Cu²⁺ + 2 Ag

7. One way to test for the presence of iron in solution is by adding potassium thiocyanate to the solution. The product when this reagent reacts with iron is FeSCN²⁺, which creates a dark red color in solution via the following net ionic equation:

Fe³⁺ + SCN^– → FeSCN²⁺

How many grams of iron sulfate would be needed to produce 2 moles of FeSCN²⁺?

1. 110 g

2. 220 g

3. 400 g

4. 500 g

8. During the assigning of oxidation numbers, which of the following elements would most likely be determined last?

1. Ar

2. F

3. Sr

4. Ir

9. As methanol is converted to methanal, and then methanoic acid, the oxidation number of the carbon:

1. increases.

2. decreases.

3. increases, then decreases.

4. decreases, then increases.

10.In the compound KH₂PO₄, which element has the highest oxidation number?

1. K

2. H

3. P

4. O

11.If a certain metal has multiple oxidation states, its acidity as an oxide generally increases as the oxidation state increases. Therefore, which of the following tungsten compounds is likely to be the strongest acid?

1. WO₂

2. WO₃

3. W₂O₃

4. W₂O₅

12.Consider the following steps in the reaction between oxalic acid and chlorine:

1. Cl₂ + H₂O → HOCl + Cl^– + H⁺

2. H₂C₂O₄ → H⁺ + HC₂O₄⁻

3. HOCl + HC₂O₄⁻ → H₂O + Cl⁻ + 2 CO₂

Which of these steps, occurring in aqueous solution, is an example of a disproportionation reaction?

1. I only

2. III only

3. I and III only

4. I, II, and III

13.Potentiometry in an oxidation–reduction titration is analogous to performing an acid–base titration with a(n):

1. acidic indicator.

2. basic indicator.

3. pH meter.

4. oxidizing agent.

14.After balancing the following oxidation–reduction reaction, what is the sum of the stoichiometric coefficients of all of the reactants and products?

S₈ (s) + NO₃⁻ (aq) → SO₃²⁻ (aq) + NO (g)

1. 4

2. 50

3. 91

4. 115

15.An assay is performed to determine the gold content in a supply of crushed ore. One method for pulling gold out of ore is to react it in a strong cyanide (CN^–) solution. The equation is provided below:

Au + NaCN + O₂ + H₂O → Na[Au(CN)₂] + NaOH

An indicator is used during this reaction, and approximately 100 mL of a 2 M NaCN solution is used to reach the endpoint. How many moles of Au are present in the crushed ore?

1. 0.01 mol

2. 0.02 mol

3. 0.10 mol

4. 0.20 mol

PRACTICE QUESTIONS