CHEM126 – CHAPTER 18 – BASIC HOMEWORK / ELECTROCHEMISTRY II

CHAPTER 18 BASIC HOMEWORK:

ELECTROCHEMISTRY II

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Question 1

Check those statements that are correct.

Explanation of standard reduction potentials

Select one or more:a. Fluoringe wants to be an ion more than bromine does because it has a larger reduction potential. b. 2Cu2+(aq) + 4e- → 2Cu(s)   Eo = = 0.67 Vc. Sn(s) → Sn2+(aq) + 2e-  Eo = = -0.14 Vd. Zinc wants to be an ion more than nickel. (Look at the oxidation potentials. For example, Zn(s) → Zn2+(aq) + 2e-  Eo = +0.76 V) 

Explanation

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Question 2

What is the voltage for the reaction under standard conditions: 2Al(s) + 3Pb2+(aq) → 2Al3+(aq) + 3Pb(s)?
Oxidation and reduction reactions
Answer:

Explanation

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Question 3

Check the statement which are correct.
Select one or more:a. The above reaction is spontaneous in the direction as written. b. Aluminum is a more active metal (larger oxiditation potential) than lead. c. The above reaction is spontaneous in the reverse direction.d. Lead s a more active metal (larger oxiditation potential) than aluminum.

Explanation

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Question 4

What is the voltage for the reaction under standard conditions: 3Ag(s) + Cr3+(aq) → 3Ag+(aq) +Cr(s)? (See above for reduction potentials.)

Standard conditions mean any amount of the solids (as long as there is some), solutions are 1 M, and gases are 1 atm.

Answer:

Explanation

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Question 5

Check the statement which are correct.
Select one or more:a. The above reaction is spontaneous in the direction as written.b. silver is a more active metal (larger oxiditation potential) than chromium.c. The above reaction is spontaneous in the reverse direction. d. Chromium is a more active metal (larger oxiditation potential) than silver. 

Explanation

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Question 6

What is the voltage under standard conditons for the reaction: 2Ag(s) + I2(s) → 2Ag+(aq) + 2I-(aq)?
Answer:

Explanation

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Question 7

Which or the following statements are true about a spontaneous oxidation-reduction reaction?
Select one or more:a. The voltage, E, associated with the reaction is positive. b. The change in free energy, ΔG, of the reaction is negative. c. The voltage, E, associated with the reaction is negative.d. The change in free energy, ΔG, of the reaction is positive.

Explanation

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Question 8

Find ΔGo in J for: Al3+(aq) + 3e- → Al(s) Eo = -1.66 V
Relation between free energy and voltage

Answer:

Explanation

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Question 9

Find ΔG in J for: X4+(aq) + 4e- → X(s) E = -1.62 V
Answer:

Explanation

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Question 10

Which statement is INCORRECT for the following exothermic reaction?

Cu2+(aq) +Zn(s) → Cu(s) + Zn2+(aq)

Select one:a. The standard voltage for the reaction as written is 1.1 V.b. A Zn strip placed in a solution of CuCl2 immediately starts to decompose into zinc ions andc. Copper ions are converted to metallic copper.d. No useful work is done as the zinc strip decomposes.e. The temperature of the solution decreases. 

Explanation

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Question 11

Which of the following statements is NOT correct about the Galvanic cell shown below?

A battery has a voltage and produces a current (flow of electrons) in a circuit. The voltage and current can be made to do useful work such as running an electric motor. A galvanic cell generates electricity like a battery.

Select one:

a. The voltage and current can be made to do useful work.b. The voltage measured by the voltmeter is 1.1 V under standard conditions.c. By means of the connecting wire metallic zinc can give electrons to copper ions which become copper atoms.d. Negative charge leaves the zinc side through the wire as electrons.e. Charge neutality is preserved on the zinc side through the salt bridge either by negative ions moving in or positive ions moving out. Thus, there is no build up of positive charge as the electrons leave.f. Negative charge enters the copper side through the wire as electrons.g. Charge neutality is preserved on the copper side through the salt bridge either by negative ions moving out or positive ions moving in. Thus, there is no build up of negative charge as the electrons enter.h. Thus, the salt bridge is necessary for the galvanic cell to work.i. The salt bridge is not necessary for the galvanic cell to work. 

Explanation

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Question 12

In the Zn-Cu galvanic cell shown above, which of the following statements are true?
Anode and Cathode defined
Select one or more:a. The half-cell with zinc is the anode. b. The half-cell with copper is the anode.c. The half-cell with zinc is the cathode.d. The half-cell with copper is the cathode. e. The zinc electrode is positive.f. The zinc electrode is negative. 

Explanation

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Question 13

What is the standard voltage or cell potential of a Cr-Hg cell? (Remember to switch one-half reaction to oxidation and to balance the number of electrons–use paper.)

Cr3+(aq)+ 3e- → Cr(s) Eo = -0.74 V
Hg2+(aq)+ 2e- → Hg(l) Eo = +0.789 V

Calculating Voltage

Answer:

Explanation

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Question 14

For the above galvanic cell which statments are correct?
Select one or more:a. 2 electrons are exchanged in the balanced reaction.
(2 electrons gained in the reduction and 2 lost in the oxiditation.)b. 3 electrons are exchanged in the balanced reaction.c. 6 electrons are exchanged in the balanced reaction. d. Cr is oxidized. e. Hg is oxidized.f. Cr3+ is reduced.g. Hg2+ is reduced. 

Explanation

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Question 15

For the reaction given below the [H+] is increased from 1.00 M to 3.00 M. What happens to the voltage? Write i for increases, n for no change, and d for decreases.

LeChatelier’s Principle

Answer: 

Explanation

Increasing the reactant concentration above the stantard concentration increases the driving force or voltage to reduce the stress of more reactant.

Question 16

For the above reaction what happens to the voltage if a larger zinc electrode is used? Write i for increases, n for no change, and d for decreases.

Solids and Equilibrium/ Voltage
Answer: 

Explanation

Recall, that the amount of a solid or pure liquid has no effect on equilibrium. A larger zinc electrode does increase the maximum current because there is more surface area for the oxidation of the zinc.

Question 17

For the above reaction the [Zn2+] is decreased from 1.00 M to 0.30 M. What happens to the voltage?
Answer: 

Explanation

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Question 18

For the above reaction the H2 pressure is increased from 1.00 atm to 4.2 atm. What happens to the voltage?
Answer: 

Explanation

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Question 19

For the above reaction the Cl- concentration is increased from 1.00 M to 4.50 M by the addition of NaCl. What happens to the voltage?
Answer: 

Explanation

The overall reaction has nothing to do with the chloride ion concentration.

Question 20

For the Zn-H2 cell, what is the voltage if [Zn2+] = 6.67 M, [H+] = 0.0194 M, and the hydrogen pressure is 18.0 atm.

The Nernst Equation

Answer:

Explanation

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Question 21

What is n (the number of moles of electrons) transferred for the following oxidation/ reduction reaction?

2Al(s) + 6H+(aq) → 2Al3+(aq) + 3H2(g)

Determining Electrons Transferred

Answer: 

Explanation

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Question 22

2Al(s) + 6H+(aq) → 2Al3+(aq) + 3H2(g)

For the above Al-H2 cell, what is the voltage if [Al3+] = 5.0561 M, [H+] = 5.3 M, and the hydrogen pressure is 0.0856 atm. Eo = 1.66 V.

Answer:

Explanation

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Question 23

In the galvanic cell below, where the process is sponataneous, on which electode is the metal deposited and what is the metal?

Select one or more:a. anodeb. cathode c. copper d. zinc

Explanation

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Question 24

In electrolysis a power supply is required to drive the reaction in the opposite direction to which it wants to go.

In the above example of electrolysis, on which electode is the metal deposited and what is the metal?
Select one or more:a. anodeb. cathode c. copperd. zinc 

Explanation

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Question 25

In the reduction of zinc ions to zinc:

Zn2+(aq) + 2e- → Zn(s)

how many moles of electrons are needed to produce 1 mole of zinc?
Answer: 

Explanation

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Question 26

If a current of 4.96 A flows for 15.32 hr, then what quantity of charge (in C) has flowed?

Current definition and calculation

Answer:

Explanation

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Question 27

In the reduction of aluminum ions to alumimum: Al3+(aq) + 3e- → Al(s)

how many moles of alumimun are produced by 0.76 moles of electrons?Answer:

Explanation

Hint, 3 moles of electrons produce 1 mole of aluminum.

Question 28

If a current of 8.70 A flows for 18.03 hr, then how many moles of electrons have flowed?
The Faraday constant
Answer:

Explanation

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Question 29

In the reduction of aluminum ions to alumimum: Al3+(aq) + 3e- → Al(s)

how many grams of alumimun are produced by a current of 1.81 A for 7.63 hr?
Answer:

Explanation

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