Electrochemistry Practice Problems for Test 4 Chapter 19 provides a comprehensive set of exercises designed to enhance understanding of key electrochemical concepts. Topics include oxidation numbers, balancing redox reactions, cell potentials, and electrolysis. The practice problems are ideal for students preparing for exams in general chemistry courses. With detailed solutions and explanations, this resource supports mastery of electrochemical principles and calculations. Perfect for reinforcing knowledge in preparation for assessments.

Key Points

  • Includes practice problems on oxidation numbers and redox reactions.
  • Covers cell potentials and electrochemical cell concepts.
  • Features detailed solutions for each practice problem.
  • Designed for students studying general chemistry and preparing for exams.
Aine Lee
13 pages
Exams
Aine Lee
13 pages
Exams
174
/ 13
1
General Chemistry II Jasperse
Electrochemistry. Extra Practice Problems
Oxidation Numbers
p1
Free Energy and Equilibrium
p10
Balancing Redox; Electrons Transferred; Oxidizing
Agents; Reducing Agents
p2
K Values and Voltage
p11
Spontaneous Voltaic Electrochemical Cells
p4
Nonstandard Concentrations and Cell Potential
p11
Cell Potentials
p5
Electrolysis
p12
Predictable Oxidation and Reduction Strength Patterns
p8
Ranking Relative Activity, Based on Observed
Reactivity or Lack Thereof
p9
Answer Key
p13
Key Equations Given for Test:
E˚
cell
=E˚
reduction
+ E˚
oxidation
∆G˚ = –96.5nE˚
cell
(∆G˚ in kJ)
E
cell
= E˚ – [0.0592/n]log Q
log K = nE˚/0.0592
Mol e
–
= [A • time (sec)/96,500]
time (sec)= mol e
• 96,500/current (in A)
t = (t
1/2
/0.693) ln (A
o
/A
t
)
ln (A
o
/A
t
) = 0.693•t /t
1/2
E = ∆mc
2
(m in kg, E in J, c = 3x10
8
m/s)
Oxidation Numbers
1. What is the oxidation number of chromium in the ionic compound ammonium dichromate, (NH
4
)
2
Cr
2
O
7
?
+3
d.
+6
+4
e.
+7
+5
2. What is the oxidation number of carbon in the ionic compound potassium carbonate, K
2
CO
3
?
+3
d.
+6
+4
e.
+7
+5
3. What are the oxidation numbers for nickel, sulfur, and oxygen in Ni
2
(SO
4
)
3
?
Ni +3; S +6; O -2
d.
Ni +2; S +2; O -2
Ni +2; S +4; O -2
e.
Ni +2; S +4; O -1
Ni +3; S +4; O -2
4. When hydrogen reacts with calcium metal, what are the oxidation numbers of the calcium and hydrogen in the CaH
2
product?
Ca(s) + H
2
(g) à CaH
2
(s)
–2 and +1
d.
0 and 0
+1 and –2
e.
+2 and –2
+2 and –1
5. What are the original and final oxidation numbers for iron in the smelting of iron from iron oxide?
Fe
2
O
3
(s) + 3CO(g) à 2Fe(s) + 3CO
2
(g)
+2 à 0
d.
+6 à 0
+3 à 0
e.
No change
0 à +2
2
Balancing Redox; Electrons Transferred; Oxidizing Agents; Reducing Agents
6. Balance the following reaction. How many electrons are transferred?
Mg + O
2
→ MgO
a. 3
b. 4
c. 6
d. 8
e. 2
7. Methanol fuel cells use the following reaction. How many electrons are transferred in this redox reaction as written?
2CH
3
OH + 3O
2
→ 2CO
2
+ 3H
2
O
3
d.
12
6
e.
2
8
8. What is the coefficient for hydroxide, and how many electrons are transferred after balancing the reaction?
Pb(OH)
4
2-
+ ClO
-
→ PbO
2
+ Cl
-
+ OH
-
+ H
2
O
2 OH
-
and 2 electrons
d.
2 OH
-
and 4 electrons
3 OH
-
and 4 electrons
e.
None of the above
1 OH
-
and 2 electrons
9. Cobalt is one of many metals that can be oxidized by nitric acid. Balance the following the reaction. How many
electrons are transferred, and what would be the coefficient for H
2
O in the balanced reaction?
Co + NO
3
–
+ H
+
→ NO + H
2
O + Co
2+
3 electrons; 2 H
2
O
d.
6 electrons; 4 H
2
O
6 electrons; 6 H
2
O
e.
None of the above
4 electrons; 2 H
2
O
10. What was oxidized and what was reduced in the following reaction?
2Hg
2+
+ N
2
H
4
→ 2Hg + N
2
+ 4H
+
Hg
2+
was oxidized; N
2
H
4
was reduced
d.
Hg
2+
was reduced; N
2
H
4
was reduced
Hg
2+
was reduced; N
2
H
4
was oxidized
e.
None of the above
Hg
2+
was oxidized; N
2
H
4
was oxidized
3
11. The following reaction occurs in basic solution. Identify the oxidizing agent. Note the reaction equation is not
balanced.
H
2
O(l) + Zn(s) + NO
3
–
(aq) + OH
–
(aq) → Zn(OH)
4
2–
(aq) + NH
3
(aq)
Zn(s)
d.
H
2
O(l) (the oxygen)
NO
3
–
(aq) (the nitrogen)
e.
NH
3
(aq) (the nitrogren)
OH
–
(aq)
12. For the following reaction, which statement, A–D, is not correct? If more than one is not correct, respond E.
2Au + 4Cl
2
→ 2AuCl
4
–2
Au is the reducing agent.
d.
The equation is fully balanced.
Cl
2
is the oxidizing agent
e.
More than one statement is not correct.
Au is oxidized.
13. Which substance is the reducing agent in the following reaction?
Ca(s) + Zn
2+
(aq) → Ca
2+
(aq) + Zn(s)
Ca(s)
d.
Zn(s)
Zn
2+
(aq)
e.
None of the above
Ca
2+
(aq)
14. Which substance is the reducing agent in the following reaction?
4H
+
(aq) + 2Cl
-
(aq) + MnO
2
(s) → Cl
2
(g) + Mn
2+
(aq) + 2H
2
O(l)
H
+
(aq)
d.
Cl
2
(g)
Cl
-
(aq)
e.
Mn
2+
(aq)
MnO
2
(s)
15. Which one of the following items does not characterize an oxidizing agent?
An oxidizing agent gains electrons.
An oxidizing agent causes another species to be oxidized.
The oxidation number of an oxidizing agent decreases.
A good oxidizing agent is a metal in a high oxidation state, such as Mn
7+
.
An example of a good oxidizing agent is an alkali metal, such as Na.
16. Which of the following statements about electrochemical cells is true?
a. Reduction occurs at the anode
b. An element with a high love for electrons is likely to be easily oxidized
c. Oxidation occurs at the anode
d. Only oxidation half–reactions are useful
e. none of the above
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FAQs

What topics are covered in the electrochemistry practice problems?
The electrochemistry practice problems cover a variety of topics essential for understanding the subject. Key areas include oxidation numbers, balancing redox reactions, and calculating cell potentials. Additionally, the problems address electrolysis and the practical applications of electrochemical cells. This comprehensive approach ensures students grasp both theoretical and practical aspects of electrochemistry.

How do the practice problems help students prepare for exams?
These practice problems are specifically designed to reinforce students' understanding of electrochemical concepts. By working through the problems, students can apply theoretical knowledge to practical scenarios, enhancing their problem-solving skills. The inclusion of detailed solutions allows for self-assessment and deeper comprehension of the material, making it an effective study tool for exam preparation.

What is the significance of balancing redox reactions in electrochemistry?
Balancing redox reactions is crucial in electrochemistry as it ensures the conservation of mass and charge in chemical equations. Understanding how to balance these reactions allows students to accurately represent the electron transfer processes that occur in electrochemical cells. This skill is fundamental for predicting the outcomes of reactions and calculating cell potentials, which are essential for analyzing electrochemical systems.

What are cell potentials and why are they important?
Cell potentials, or electromotive forces, are measures of the voltage generated by an electrochemical cell. They indicate the tendency of a chemical reaction to occur spontaneously. Understanding cell potentials is vital for predicting the direction of electron flow in electrochemical reactions and for determining the feasibility of reactions under standard and non-standard conditions. This knowledge is essential for applications in batteries, fuel cells, and other electrochemical technologies.