What is the difference between an electrolytic cell and a voltaic cell? 2. .... Water. Review. Questions. 1. What purpose does the carbon rod serve in...
CK-12 Chemistry Concepts - Intermediate Answer Key Chapter 23: Electrochemistry 23.1 Direct Redox Reactions Practice Questions Watch the video at the link below and answer the following questions: http://www.youtube.com/watch?v=2MawIDT5DFU 1. What happened when Mg and Zn were placed in the Pb2+ solution? 2. Did the Zn strip react in the Mg2+ solution? 3. How was Ag shown to be least reactive? Answers 1. Both reacted to form Pb metal. 2. No, Zn is less reactive. 3. Ag in Cu2+ did not react, but Cu in Ag+ did react. Review Questions 1. What metals are high in the activity series? 2. What metals are low in the activity series? 3. Is tin easier to oxidize than magnesium? Answers 1. Those that oxidize easily. 2. Those that are hard to oxidize. 3. No, it is lower than magnesium in the series and more difficult to oxidize. 23.2 Electrochemical Reaction Practice Questions Read the material at the link below and answer the following questions: 1
Spontaneous reactions occur in what type of system? Nonspontaneous reactions occur in what type of system? What is potential? How is potential measured?
Answers 1. 2. 3. 4.
Batteries or galvanic cells. Electrolytic or electroplating cells. A quantitative description of the driving force behind an electrochemical reaction. Volts.
Review Questions 1. What is an electrochemical reaction? 2. What type of chemical reaction is involved? 3. What needs to be able to move in an electrochemical reaction? Answers 1. Reaction that involves interconversion of chemical energy and electrical energy. 2. Redox reactions. 3. Electrons and ions. 23.3 Voltaic Cells Practice Questions Read the material at the link below and answer the following questions: http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/GalvanicCells/chemprime/CoreChem3AElectrochemical_Cells-699.html 1. 2. 3. 4.
What is the difference between an electrolytic cell and a voltaic cell? Where does the oxidation reaction take place in a voltaic cell? Where does the reduction reaction take place? List some examples of voltaic cells that are of commercial importance.
Answers
2
1. An electrolytic cell uses an outside source of electric current to cause a nonspontaneous reaction to occur. A voltaic cell creates an electric current through a spontaneous reaction that releases electrons. 2. The anode. 3. The cathode. 4. Dry cells, mercury cells, rechargeable Ni-Cd batteries, and lead storage cells. Review Questions 1. What does a voltaic cell do? 2. Why are the two electrodes physically separated? 3. What is the purpose of the porous membrane? Answers 1. Creates a flow of electrons through a spontaneous reaction. 2. So the electrons will flow through the external circuit. 3. To allow anions to move so as to balance changes in cation concentration. 23.4 Electrical Potential Practice Questions Read the material at the link below and answer the following questions: http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1920/nernst-bio.html 1. Where was Nernst born? 2. What theory did he develop in 1889? 3. What musical instrument did he develop that musicians did not like? Answers 1. Briesen, West Prussia. 2. The theory of galvanic cells. 3. An electrical piano. Review Questions 1. Why can’t we measure the electrical potential of an isolated half-cell? 2. What does the reduction potential tell us? 3
3. What is the cell potential? Answers 1. There is no other half-reaction taking place to complete the oxidation-reduction process. 2. The tendency of a given half-reaction to occur as a reduction. 3. The difference in reduction potential between the two-half-cells. 23.5 Standard Hydrogen Electrode Practice Questions Watch the video at the link below and answer the following questions: http://www.youtube.com/watch?v=mrOm6xZip6k 1. Why does a cation move through the salt bridge to the hydrogen side? 2. Why is the zinc half-cell the anode? 3. How is the standard potential defined? Answers 1. Because protons are being consumed on the hydrogen side and need the decrease in positive charges balanced by the Na+. 2. Because that us where oxidation occurred. 3. As a reduction. Review Questions 1. What is the defined potential of the hydrogen electrode? 2. What is the chemical composition of this electrode? 3. What are the standard conditions for the other half-cell? Answers 1. Zero volts. 2. Hydrogen gas at one bar bubbling through a 1.0 M solution of a strong acid at 298K. 3. A 1.0 M solution of the metal salt at 298K.
4
23.6 Calculating Standard Cells Potentials Practice Questions Read the material at the link below and answer the questions at the end: http://chemwiki.ucdavis.edu/Analytical_Chemistry/Electrochemistry/Voltaic_Cells/The_C ell_Potential#Problems Answers Answers are given on the web site. Review Questions 1. What type of reaction will the half-cell with the highest reduction potential undergo? 2. What sign must the overall cell potential be in order for a reaction to be spontaneous? 3. Is Zn2+ a stronger or weaker reducing agent than Mg2+? Answers 1. Reduction. 2. Positive. 3. Weaker, because zinc is above magnesium in the table. 23.7 Batteries Practice Questions Read the material at the link below and answer the following questions: http://www.fueleconomy.gov/feg/fuelcell.shtml also click on the fuel stack term highlighted on the page.
5
1. 2. 3. 4.
Where does hydrogen enter the fuel cell? How are electrons produced? Where do the electrons go? What is the product of the fuel cell reaction?
Answers 1. 2. 3. 4.
At the anode. Hydrogen gas splits into hydrogen ions and electrons. The electrons flow through a circuit that provides power to the car motor. Water.
Review Questions 1. What purpose does the carbon rod serve in a dry cell? 2. Where does an alkaline battery get its name? 3. Why is recharging a car battery not 100% efficient. Answers 1. As a conductor of the electric current. 2. It contains a base. 3. Some of the solid lead sulfate falls off the poles. 23.8 Electrolytic Cells Practice Questions Watch the video at the link below and answer the following questions : http://www.youtube.com/watch?v=y4yYF8gSHdA 1. What was the source of electricity? 2. What was the purpose of the steel attached to an electrode? 3. What is used to help carry the electric current? Answers 1. A battery charger. 2. To carry electrons through the circuit. 3. Washing soda (not baking soda). Review 6
Questions 1. What would be the products of a spontaneous reaction between Zn/Zn2+ and Cu/Cu2+? 2. How do we know that the reaction forming Cu2+ is not spontaneous? 3. What would be the voltage for the reaction where Zn metal forms Zn2+? Answers 1. Cu(s) and Zn2+(aq). 2. The standard cell potential is negative. 3. +0.76 volts. 23.9 Electrolysis of Water Practice Questions Watch the video at the link below and answer the following questions: www.youtube.com/watch?v=HQ9Fhd7P_HA 1. 2. 3. 4.
What are the electrodes? What is the power source? What is put in the water to facilitate flow of electricity Which test tube contains hydrogen gas?
Answers 1. 2. 3. 4.
Two thumb tacks. A nine-volt battery. Baking soda (sodium bicarbonate). The one that contains twice as much gas as the other tube.
Review Questions 1. What are the electrodes used in the reaction? 2. Why is sulfuric acid used? 3. At which electrode does oxygen appear? Answers 1. Platinum. 7
2. Pure water does not conduct electricity well. 3. The anode
23.10 Electrolysis of Molten Salts and Electrolysis of Brine Practice Questions Read the material at the link below and answer the following questions:
http://www.citycollegiate.com/sblock1.htm
1. How is sodium removed from the cell? 2. Why is CaCl2 added to the system? 3. Why doesn’t metallic calcium contaminate the sodium production? Answers 1. The molten sodium collects in the cathode compartment and is then removed from the cell through a pipe. 2. CaCl2 is added to the cell so that the NaCl and Na don’t form a molten fog, which is impossible to separate. 3. Since the sodium and calcium have different densities, they do not mix. Review Questions 1. What are the products of the electrolysis of molten NaCl? 2. What are the products of the electrolysis of aqueous NaCl? 3. What spectator ion is not shown in the overall equation for the electrolysis of aqueous NaCl? Answers 1. Sodium metal and chlorine gas. 2. Chlorine gas, hydrogen, and hydroxide. 3. Sodium. 23.11 Electroplating 8
Practice Questions Watch the video at the link below and answer the following questions: http://www.youtube.com/watch?v=Q8Xo43sfLgY 1. 2. 3. 4.
What is the solution used? How did he test the system? Why are batteries better than wall current for the electrical current? What was the anode?
Answers 1. 2. 3. 4.
Nickel ammonium sulfate. He used a penny to check the plating. Current flow is smoother. A nickel plate.
Review Questions 1. In the electroplating with copper, what is the anode? 2. What supplies the electric current? 3. What other metals can be coated onto objects? Answers 1. A copper strip. 2. A battery. 3. Gold, silver, chromium, platinum.
