CK-12-Chemistry Intermediate

http://www.ck12.org Chapter 23. Electrochemistry

2. What sign is assigned to the cathode in a voltaic cell? In an electrolytic cell?


3. What is produced at the anode of a Down’s cell? At the cathode?


4. Why can’t sodium metal be manufactured by the electrolysis of brine?


5. Write the half-reaction that occurs at the cathode during the electroplating of chromium metal from a solution
   of chromium(III) nitrate.

Problems

6. Aluminum metal is obtained by a process that involves the electrolysis of molten aluminum oxide (Al 2 O 3 ).
   Write the half-reaction that occurs at the cathode.


7. Consider the electrolysis of molten potassium bromide.
   a. Write the equations for the half-reactions that occur at each electrode.
   b. Write the overall redox reaction.
   c. Use the Standard Reduction Potentials at 25°C table (in the lesson “Cell Potentials”) to calculate the
   minimum voltage of the battery used to electrolyze potassium bromide.


8. Consider the electrolysis of water.
   a. Write the equation for the overall reaction.
   b. In a certain electrolysis experiment, 2.20 L of oxygen gas is produced. What volume of hydrogen gas is
   produced?


9. During the electrolysis of molten sodium chloride in a Down’s cell, 356 L of chlorine gas is produced at a
   temperature of 850°C and a pressure of 1.00 atm.
   a. How many moles of chlorine gas are produced? (Hint: Use ideal gas law with R = 0.0821 L•atm/K•mol)
   b. How many moles of sodium metal are produced in the same process?
   c. What mass of sodium is produced?


10. An electrolytic cell is constructed with a Pb|Pb^2 +anode and a Cd|Cd^2 +cathode.
    a. Write the half reactions for each electrode and the overall reaction.
    b. Calculate the standard cell potential.
    c. The cell is run for a certain amount of time in which the mass of the lead electrode decreases by 1.00 g.
    By how much does the mass of the cadmium electrode increase in the same time?

Further Reading / Supplemental Links

• The Extraction of Metals –An Introduction, (http://www.chemguide.co.uk/inorganic/extraction/introduction.html


• Electrolytic Cells, (http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch20/faraday.php

Points to Consider

Aluminum is widely used in all sorts of modern materials from beverage cans to airplanes.

• Why was pure aluminum metal so difficult and expensive to obtain prior to the development of electrolysis on
  an industrial scale?


• How much energy savings comes from recycling aluminum instead of producing it from aluminum ore?