b. In potassium permanganate the manganese acts as an acid-forming element. It also acts as a base-forming element in certain compounds. Try the action of ammonium sulfide, ammonium carbonate, and sodium hydroxide, respectively, on a solution of manganese chloride (?).

EXERCISE 100

A STUDY OF SOME OF THE COMPOUNDS OF CHROMIUM

Apparatus. 6 test tubes.

(OPTIONAL)

Materials. Solution of potassium chromate (RS.); lead acetate solution (R. S.); barium chloride solution (R. S.); ammonium sulfide (R.S.); sodium carbonate solution (R. S.); sodium hydroxide solution; 0.5 g. chromium chloride or chromium sulfate dissolved in 25 cc. water.

a. Chromates and dichromates. Write the formula for potassium chromate; for potassium dichromate. Is the chromium an acid-forming or a base-forming element in these compounds? Add 2 or 3 drops of sulfuric acid to a little potassium chromate solution (?).

b. Try the effect of a solution of potassium chromate on a solution of a compound of lead (R); also on a compound of barium (R).

c. Salts of chromium. Try the action of each of the following compounds on a solution of chromium chloride or chromium sulfate: ammonium sulfide, sodium carbonate, sodium hydroxide. Describe the results and write the equations for the reactions involved.

BORAX-BEAD TESTS (OPTIONAL)

Apparatus. Platinum wire; burner.

Materials. Borax (R. S.); small piece (size of a pin's head) of a compound of each of the following metals: nickel, iron, manganese, copper.

Recall the effect of adding a trace of cobalt nitrate to a borax bead (Exercise 69). Repeat the experiment, substituting for the cobalt nitrate, salts of the following metals: nickel, iron, manganese, copper (?).

APPENDIX A

TABLE OF CONSTANTS

LIST OF THE COMMON ELEMENTS, THEIR SYMBOLS, AND THEIR ATOMIC WEIGHTS

TENSION OF AQUEOUS VAPOR AT VARIOUS TEMPERATURES, EXPRESSED IN MILLIMETERS OF MERCURY

This system is now used in all civilized countries with four or five exceptions. The United States and Great Britain are among the few countries that have not formally adopted it, but even in these countries the system is universally used by scientists and is coming into use more and more by manufacturers.

In the metric system each unit is 10 times as large as the next lower unit; hence the system is often termed the "decimal system."

1. Length. The unit is the meter. It is equal to 39.37 inches.

10 millimeters (mm.) = 1 centimeter (cm.)

10 centimeters =

1 decimeter (dm.)

10 decimeters = 1 meter (m.)

1000 meters = 1 kilometer (km.)

The only measures of length ordinarily used by the chemist are the millimeter and the centimeter; thus, the height of the barometer at the sea level is recorded as 76 cm. (or more commonly as 760 mm.), and not 7 dm. and 6 cm.

2. Volume. The unit generally used is the cubic centimeter. 1000 cubic millimeters 1 cubic centimeter (cc.)

1000 cubic centimeters

1 cubic decimeter

=

1 liter

1000 cubic decimeters = 1 cubic meter

The chemist uses only the cubic centimeter and the liter as measures of volume. Thus, the volume of a test tube is given as (say) 25 cc.; that of a flask as (say) 500 cc., or liter.

3. Weight. The unit is the gram. This is approximately the weight of 1 cc. of pure water at its temperature of greatest density (4°). It is equal to 15.43 grains.

10 milligrams (mg.) = 1 centigram (cg.)

10 centigrams = 1 decigram (dg.)

10 decigrams = 1 gram (g.)

1000 grams 1 kilogram (kg.)

The gram and kilogram are the units of weight most generally used by the chemist. Thus, the weight of a crucible is given as (say) 10.532 g. and not 10,532 mg. or 10 g. 5 dg. 3 cg. 2 mg.