AP Chemistry - Electrochemistry Worksheet #7
Electolytic Stoichiometry
1.  What electrical charges do the anode and the cathode carry in an electrolytic cell?
 
2. Why must electrolysis occur in order for electrolytic conduction to continue?
 
3. Write the anode, cathode, and overall reactions for the electrolysis of molten NaCl.
 
4. What happens to the pH of the solution near the cathode and anode during the electrolysis of KNO3?
 
5. Write the anode reaction for the electrolysis of an aqueous solution that contains 
(a) NO3-
(b) Br- and 
(c) NO3- and Br-
 
6. What products would we expect at the electrodes if a solution containing both KBr and Cu(NO3)2 were electrolyzed?
 
7. How many Farads are required to reduce 10 g of calcium  from melted calcium chloride?
 
8. A current of 5.0 amp is passed through melted KCl for 1000 sec.  How many grams of potassium are produced?
 
9.  How much time is required to reduce 20.0 g of silver from a solution of silver nitrate, using 15.0 amp of current?
 
10. a) How many grams of copper are deposited from a plating bath by a current of 3.0 amperes flowing for a period of 2.0 hours?
b) How many litres of oxygen gas will be evolved at the anode if the temperature is 27oC and the pressure is 98.6 kPa?
c) If the cell originally contained 1.0 litre of 0.20 M CuSO4 and a platinum (inert) anode, what is the concentration of CuSO4 after the electrolysis assuming no volume change?
d) If the anode is a bar of copper, what is the concentration of CuSO4 after the electrolysis?
 
11. How many litres of H2 are evolved at 20oC and 99 kPa when 2.0 amps is passed for 3.0 hours through a cell containing sulphuric acid?
 
12. a) Explain why the silver and gold found in blister(impure) copper do not go into solution when the anode disintegrated during the electrolytic refining of copper.
b) If Ag+ ions were present in the electrolyte, would they interfere with the production of pure copper cathodes? Explain.
c) If Al3+ ions were present, would they interfere with the production of pure copper cathodes? Explain.
 
13. How many coulombs are passed through an electrolysis cell by 
(a) a current of 4.00 A for 600 s?
(b) a current of 10.0 A for 20 min?
(c) a current of 1.5 A for 6.00 hr?
How many faradays correspond to the answers above?
 
14. How many faradays are required to 
(a) reduce 0.20 mol Fe2+ to Fe? 
(b) oxidize 0.70 mol Cl- to Cl2
(c) reduce 1.50 mol Cr3+ to Cr? 
(d) oxidize 1.0 X 10-2 mol Mn2+ to MnO4-?
 
15. How many grams of Fe(OH)2 are produced at an iron anode when a basic solution undergoes electrolysis at a current of 12.0 A for 10.0 min?
 
16. How many faradays are required to
(a) produce 5.00 g Mg from molten MgCl2?
(b) form 41.0 g Cu from CuSO4 solution?
 
17. How many millilitres of gaseous H2, measured at STP,  would be produced at the cathode in the electrolysis of water with a current of 1.50 A for 5.00 min?
 
18. How many moles of Cr3+ would be reduced to Cr by the same amount of electricity that produces 10.0 g Ag from a AgNO3 solution?
 
19. A solution of NaCl in water was electrolyzed with a current of 3.00 A for 10.0 min.  How many millilitres of 0.100 M HCl would be required to neutralize the resulting solution?
 
20. How many hours would it take to produce 25.0 g of metallic chromium by the electrolytic reduction of Cr3+  with a current of 1.25 A?
 
21. How many hours would it take to generate 25.0 g lead from PbSO4 during the charging of a storage battery using a current of 0.50 A?  The half-reaction is 

               PbSO4 + 2 e- ---> Pb + SO42-
 

21. How many amperes would be needed to produce 48.0 g of magnesium during the electrolysis of molten MgCl2 in 1.00 hr?
 
22. A large electrolysis cell that produces metallic aluminum from Al2O3 by the Hall process is capable of yielding 409 kg of aluminum in 24 hr.  What current is required?
 
23. How many grams of Cl2 would be produced in the electrolysis of NaCl by a current of 2.50 A for 40.0 min?
 
24.   A solution containing vanadium (chemical symbol - V) in an unknown oxidation state was electrolyzed with a current of 1.50 A for 30 min.  It was found that 0.475 g of V was deposited on the cathode.
(a) How many equivalents of V were deposited?
(b) How many moles of V were deposited?
(c) What was the original oxidation state of the V ion?
 
25. Predict the products that will appear if a solution of Cu(NO3)3 is electrolyzed. Give the net cell reaction.