CHM1 20 End-of-Chapter Problems Collection

1. Which electrode oxidizes the solution in the half-cell? Anode or Cathode?

2. Why is the Standard Hydrogen Electrode important to calculating cell potentials?

3. Identify the which side is the cathode and which side is the anode. 

Ag(s) | Ag+(aq)(.5M) || Ag⁺(aq) (.05M) | Ag(s)

4. Why is it important to use an inert electrode in situations like the SHE?

5. What is the standard half cell potential for the SHE?

6 .Consider the following two reactions:i) Cu_²⁺(aq) + Ba_(s) ? Cu_(s) + Ba²⁺_(aq)

ii) Al_(s) + Sn²⁺_(aq) ? Al³⁺_(aq) + Sn_(s)

a. Split the reaction into half reactions and determine their E^o value. Indicate which would be the anode and cathode.

b. Construct a cell diagram for the following each reactions.

c. Determine the E^o_cell for the voltaic cell formed by each reaction.

7. For this redox reaction  
Sn(s) + Pb²⁺(aq) --> Sn²⁺(aq) + Pb(s)
write out the oxidation and reduction half reactions. Create a cell diagram to match your equations.
8. From the image above, of the cell diagram, write the overall equation for the reaction.
9. If Cu2+ ions in solution around a Cu metal electrode is the cathode of a cell, and K+ ions in solution around a K metal electrode is the anode of a cell, which half cell has a higher potential to be reduced?
10. What type of reaction provides the basis for a cell potential?
11. How is the cell potential measured and with what device is it measured?
12. The Eocell for the equation

13. Predict the products of electrolysis by filling in the graph:

14. Calculate the quantity of electrical charge needed to plate 1.386 mol Cr from an acidic solution of K₂Cr₂O₇according to half-equation

H₂Cr₂O₇(aq) + 12H⁺(aq) + 12e^– ? 2Cr(s) + 7 H₂O(l)

15. Hydrogen peroxide, H₂O₂, can be manufactured by electrolysis of cold concentrated sulfuric acid. The reaction at the anode is 

2H₂SO₄ ? H₂S₂O₈ + 2H⁺ + 2e^–

When the resultant peroxydisulfuric acid, H₂S₂O₈, is boiled at reduced pressure, it decomposes:

2H₂O + H₂S₂O₈ ? 2H₂SO₄ + H₂O₂

Calculate the mass of hydrogen peroxide produced if a current of 0.893 flows for 1 hour.

16. The electrolysis of dissolved Cholride sample can be used to determine the amount of Chloride content in sample.  At the cathode, the reduction half reaction is Cl²⁺(aq) + 2 e^- -> 2 Cl^-.  What mass of Chloride can be deposited in 6.25 hours by a current of 1.11 A?

17.  In an electrolytic cell the electrode at which the electrons enter the solution is called the ______ ; the chemical change that occurs at this electrode is called _______.

 

1. anode, oxidation
2. anode, reduction
3. cathode, oxidation
4. cathode, reduction
5. cannot tell unless we know the species being oxidized and reduced.

18. How long (in hours) must a current of 5.0 amperes be maintained to electroplate 60 g of calcium from molten CaCl₂?

1. 27 hours
2. 8.3 hours
3. 11 hours
4. 16 hours
5. 5.9 hours

19. How long, in hours, would be required for the electroplating of 78 g of platinum from a solution of [PtCl₆]^2-, using an average current of 10 amperes at an 80% electrode efficiency?

 

1. 8.4
2. 5.4
3. 16.8
4. 11.2
5. 12.4

20.  How many faradays are required to reduce 1.00 g of aluminum(III) to the aluminum metal?  

1. 1.00
2. 1.50
3. 3.00
4. 0.111
5. 0.250

21. Find the standard cell potential for an electrochemical cell with the following cell reaction.

Zn(s) + Cu²⁺(aq) ? Zn²⁺(aq) + Cu(s)

22. Find ?G for the following combined half reactions:

F²_(g) + 2e^- ? 2F^-_(aq)    

Li⁺_(aq) + e^- ? Li_(s)

23. Find the equilibrium constant (K) for the following reaction: (Hint: Find E°_Cell first!)

Zn_(s) + 2H⁺_(aq) ? Zn²⁺_(aq) + H_2(g)

24. Find E°_Cell for the given reaction at standard conditions:

Cu⁺_(aq) + e^- ? Cu_(s)

I_2(s) + 2e^- ? 2I^-_(aq)

25. Make a sketch of the voltaic cell represented with the line notation. Write the overall balanced equation fro the reaction and calculate the E°_cell. Mn(s)|Mn²⁺(aq)||ClO₂^-(aq)|ClO₂(g)|Pt(s)

Remember what the single and double lines represent to assist you in this drawing. You may draw this by hand and insert a picture into your word document.

26. Calculate E°_cell for each balanced redox reaction and determine whether the reaction is spontaneous as written.

a)      2Cu(s) + Mn²⁺(aq) --> 2Cu⁺(aq) + Mn(s)

b)      MnO₂(s) + 4H⁺(aq) + Zn(s) --> Mn²⁺(aq) +2H₂O(l) + Zn²⁺(aq)

c)       Cl₂(g) + 2F^-(aq) --> F₂(g) + 2Cl^-

27. A voltaic cell employs the redox reaction:Sn²⁺(aq) + Mn(s)   Sn(s) + Mn²⁺(aq)

Calculate the cell potential at 25 degrees C under each set of conditions (Hint: you will need the Nernst equation for this):
a) standard conditions
b) [Sn²⁺] = 0.0100 M; [Mn²⁺] = 2.00 M
c) [Sn²⁺] =2.00 M; [Mn²⁺] =  0.0100 M

28. Draw an electrolytic cell in which Mn²⁺ is reduced to Mn and Sn is oxidized to  Sn²⁺. Label the anode and cathode, indicate the direction of electron flow, and write an equation for the half reaction occurring at each electrode. What minimum voltage is necessary to drive the reaction? (Again you can do this by hand and then insert a picture).

Answers to Chapter 21 Problems