oxidation-reduction.....aim 4

what are electrolytic cells?

.....aim 3

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aims.....

 

HW From textbook “CHEMISTRY a Contemporary Approach”

 

An electrolytic cell requires electrical energy to produce chemical change. This process is known as electrolysis.

 

Example

An electrolytic cell is used to plate a metallic object (ex: a spoon) with a layer of another metal (ex: silver)  the process is called electroplating.

 

Problem

Draw an electrolytic cell representing  the electroplating of a fork with gold.

 

Example

An electrolytic cell is used to produce Na(l) (a very active metal) and Cl2(g) (a very dangerous gas) from the electrolysis of  NaCl (l)

Problem

Draw an electrolytic cell showing the production of  Li(l) and F2(g) from the electrolysis LiF(l)

 

Example 

An electrolytic cell is used to produce pure metal (ex: 99.9 % nickel) from impure metal (ex: 60.7 % nickel) the process is called electrorefining.

 

Problem

Draw an electrolytic cell showing the electrorefining of chromium.

 

Example 

An electrolytic cell is used to produce H2(g) and O2(g) from the electrolysis of water.

 

Problem

Draw an electrolytic cell showing the electrolysis of NH3(l) to produce H2(g) and N2(g)

 

TEST YOUR UNDERSTANDING

8/07

Base your answers to questions 83 and 84 on the information below.

Electroplating is an electrolytic process used to coat metal objects with a more expensive and less reactive metal. The diagram below shows an electroplating cell that includes a battery connected to a silver bar and a metal spoon. The bar and spoon are submerged in AgNO3(aq).

83 Explain why AgNO3 is a better choice than AgCl for use in this electrolytic process.

84 Explain the purpose of the battery in this cell.

1/06

Base your answers to questions 84 and 85 on the information and diagram below. The apparatus shown in the diagram consists of two inert platinum electrodes immersed in water. A small amount of an electrolyte, H2SO4, must be added to the water for the reaction to take place. The electrodes are connected to a source that supplies electricity.

84 What type of electrochemical cell is shown?

85 What particles are provided by the electrolyte that allow an electric current to flow?

6/06

24 Which process occurs at the anode in an electrochemical cell?  (1) the loss of protons (2) the loss of electrons (3) the gain of protons (4) the gain of electrons

Base your answers to questions 78 through 81 on the information below. Aluminum is one of the most abundant metals in Earth’s crust. The aluminum compound found in bauxite ore is Al2O3. Over one hundred years ago, it was difficult and expensive to isolate aluminum from bauxite ore. In 1886, a brother and sister team, Charles and Julia Hall, found that molten (melted) cryolite, Na3AlF6, would dissolve bauxite ore. Electrolysis of the resulting mixture caused the aluminum ions in the Al2O3 to be reduced to molten aluminum metal. This less expensive process is known as the Hall process.

78 Write the oxidation state for each of the elements in cryolite.

79 Write the balanced half-reaction equation for the reduction of Al3+ to Al.

80 Explain, in terms of ions, why molten cryolite conducts electricity.

81 Explain, in terms of electrical energy, how the operation of a voltaic cell differs from the operation of an electrolytic cell used in the Hall process. Include both the voltaic cell and the electrolytic cell in your answer.

8/06

5 Which statement is true about oxidation and reduction in an electrochemical cell?

        (1) Both occur at the anode.  (2) Both occur at the cathode.

        (3) Oxidation occurs at the anode and reduction occurs at the cathode. (4) Oxidation occurs at the cathode and reduction occurs at the anode.

1/04

24 Which energy transformation occurs when an electrolytic cell is in operation?
        (1) chemical energy electrical energy (2) electrical energy chemical energy (3) light energy heat energy (4) light energy chemical energy

44 The diagram below shows a key being plated with copper in an electrolytic cell.

 Given the reduction reaction for this cell: Cu2+ (aq) +2e- ---> Cu(s) This reduction occurs at
        (1) A, which is the anode (2) A, which is the cathode (3) B, which is the anode (4) B, which is the cathode

6/03

Base your answers to questions 57 and 58 on the information below.

Two chemistry students each combine a different metal with hydrochloric acid. Student A uses zinc, and hydrogen gas is readily produced. Student B uses copper, and no hydrogen gas is produced.

57. State one chemical reason for the different results of students A and B. 

58. Using Reference Table J, identify another metal that will react with hydrochloric acid to yield hydrogen gas. 

63. State one difference between voltaic cells and electrolytic cells. Include information about both types of cells in your answer.

8/03

48 A voltaic cell differs from an electrolytic cell in that in a voltaic cell
        (1) energy is produced when the reaction occurs       (2) energy is required for the reaction to occur
        (3) both oxidation and reduction occur                         (4) neither oxidation nor reduction occurs

6/02

Which process requires an external power source?  (1) neutralization     (2) synthesis     (3) fermentation       (4) electrolysis

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