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CHAPTER XIII

IONIZATION

72. Conducting power of various solutions. a. Obtain a conductivity apparatus (Fig. 36) from the storeroom and polish the copper-wire electrodes with emery paper until they are bright and free from oxide. At the beginning of each experiment see that the electrodes are bright and dry, and

B

C

A

FIG. 36

that the cell A is also perfectly clean and dry. Unscrew a lamp C from a convenient socket above your desk, screw it loosely into the socket on your apparatus, and attach the apparatus to the empty socket on the lighting system by means of the extension cord and plug B. Every time a change is to be made in the cell, loosen the lamp in the socket, and do not screw it down to make contact until all the connections of the cell have been arranged.

b. Partly fill the cell A with dry powdered salt, dip the electrodes into the powder, arrange the connections at the

binding-posts, and screw down the lamp C. Have you any evidence that the powdered salt is a conductor?

c. In a similar way test the conductivity of distilled water and tap water.

d. Dissolve about 1 g. of the salt in 10 cc. of distilled water and test the conductivity of the solution. Account for the result as compared with the results obtained in b and c.

e. Repeat b and d, substituting sugar for salt. Account for any difference in results.

73. Acids from the standpoint of the ionization theory. a. Test the conductivity of dilute solutions of the following acids: hydrochloric, sulfuric, acetic.

b. Ask the instructor for a solution of dry hydrogen chloride in benzene or toluene. Determine whether it conducts the electric current (care must be taken to exclude all moisture). Pour a little of the solution on a clean, dry iron nail. Repeat, using the ordinary aqueous solution. Account for the difference in action between the two solutions. Characterize acids from the standpoint of the ionization theory on the basis that the above acids are typical ones and that all others act like them.

74. Relative strength of acids. a. Obtain from your instructor about 15 cc. of twice normal solutions of each of the following acids: hydrochloric, sulfuric, and acetic. Test their relative conductivities (Fig. 36) by noting the brilliancy of the light evolved in each case (three students should work together, each using a different acid). Note the results.

b. From the standpoint of the ionization theory, upon what does the relative strength of two acids in equimolecular concentration depend? How will this affect the rate at which the two acids will act upon a third substance? Will the two acids, when treated with a metal, evolve hydrogen at the same rate? Will the volume of hydrogen ultimately evolved be the same? Test your statements by determining the rate at which each of the three acids used in a will give up hydrogen when brought in contact with zinc. To do this proceed as follows:

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