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is in the upper part of the tube. Be careful not to lift the mouth of the tube from the water.

What are the white fumes that come from the phosphorus ? What causes the fumes? What gas is being used up?

3. Allow the apparatus to stand until the next day. Note the position of the water. Why has it risen in the tube? Are white fumes rising from the phosphorus now? Why? What is the gas that remains in the tube?

4. Lower the tube until the water within and the water without the tube stands at the same level. Why? Note the volume of the gas in the tube.

5. Slip a cover glass over the mouth of the tube and remove it from the jar. To further test the remaining gas thrust into the tube a blazing splint. Does the gas burn? Does it support combustion? What is the gas?

6. Record your observations and calculate the per cent of nitrogen in the air, as follows:

(a) Volume of air at the beginning of experiment = (b) Volume of nitrogen at the end of the experiment (c) Volume of oxygen removed by the phosphorus Volume of oxygen (c)

=

CC.

CC.

=

CC.

= volume of air (a) volume of nitrogen (b). The per cent of nitrogen by volume in the air is found as follows:

Volume of nitrogen (b) × 100

Volume of air (a)

% nitrogen

The per cent of oxygen by volume in the air is found in like

manner:

Volume of oxygen (c)×100
Volume of air (a)

=

% oxygen

B. Carbon Dioxide in the Air.

(Student's Experiment.)

1. Place about 5 cc. of limewater in a clean beaker and leave it exposed to the air until the close of the laboratory period. Note the white crust formed on the surface of the limewater. This proves the presence of carbon dioxide in the air.

2. Through the long glass elbow blow air from the lungs into 5 cc. of limewater in a test tube. Explain results. This is one source of carbon dioxide in the air.

3. Place a burning splint in a bottle of air. In a short time the splint will go out. Why? Remove the splint and quickly cover the bottle with a glass plate. Add 5 cc. of limewater and shake. Results? How does this experiment show another source of carbon dioxide in the air?

4. Name three other sources of carbon dioxide in the air.

5. If animals are constantly exhaling carbon dioxide, why does not the per cent of oxygen greatly decrease and the per cent of carbon dioxide increase as time goes on?

C. Water Vapor in the Air.

1. Place a piece of calcium chloride on a watch glass or in a dry beaker and leave it exposed to the air overnight. (Lock it in your drawer.) In twenty-four hours look at it again. Explain. A substance that will take up water from the air in this way is a deliquescent substance. Such substances are good drying agents.

2. In what other way could you prove the presence of water vapor in the air?

3. What are some of the sources of water vapor in the air?

MATERIALS.

EXPERIMENT 19

Ammonia, NH3

Ammonium chloride (10-g. portions), slaked lime (20-g. portions), concentrated hydrochloric acid, red litmus solution, splints, red litmus paper, and blue litmus paper. APPARATUS. Large test tube, one-hole rubber stopper, long elbow, 4 gas bottles dry, 2500-cc. beaker, cover glasses.

A. Preparation of Ammonia.

1. Obtain 10 grams of ammonium chloride and 20 grams of calcium hydroxide (slaked lime). Smell of each. Has either an odor? Now mix them well on a paper with a stirring rod and smell again. What is the odor? Put the mixture in the large test tube. Insert the one-hole stopper with the long elbow. Clamp the test tube in the ring stand, with the outlet tube turned up. Heat the test tube gently. Collect three bottles of the gas by inverting the bottle over the tube and holding it there until a drop of hydrochloric acid held on a stirring rod at the mouth of the bottle fumes strongly. Is ammonia heavier or lighter than air? Write the word-and-symbol equation for the reaction that takes place in the preparation of ammonia.

2. Turn the outlet tube down and insert it into a bottle containing about 20 cc. of water. The tube must not touch the water. Why? Heat the mixture until no more gas is given off. (While heating, test the properties of the gas collected.)

B. Properties of Ammonia.

1. What is the color and odor of ammonia?

2. Moisten your finger and hold it in the gas. Touch it to the tongue. What is the taste of ammonia?

3. Fill your large beaker with water and color it with a few drops of red litmus solution. Uncover a bottle of ammonia and quickly thrust its mouth into the water. Hold it in this position for five minutes. Result? Why not collect ammonia over water?

4. Put a few drops of hydrochloric acid in a bottle; cover and shake well. Place it mouth downward over a bottle

of ammonia and remove the glass covers. Result? Explain and write the equation.

5. Thrust a lighted splint into a bottle of ammonia. Does it burn or support combustion?

6. Remove the outlet tube from the bottle containing the liquid. Smell the liquid. Test it with red and with blue litmus. The gas ammonia combined with the water to form ammonium hydroxide.

NH3+H2O→NH4OH

For what purpose is this liquid used in the home? It is commonly called "ammonia." Is this correct? Explain.

V. ACIDS, BASES, AND SALTS

EXPERIMENT 20

General Properties of Acids, Bases, and Salts

MATERIALS. Sulfuric acid, hydrochloric acid, nitric acid, acetic acid, crystals of tartaric acid, red litmus paper, blue litmus paper, magnesium ribbon pieces 1 cm. long, sodium hydroxide, potassium hydroxide, ammonium hydroxide, calcium hydroxide solution (limewater), sodium chloride, potassium sulfate, ammonium chloride, sodium carbonate, phenolphthalein, methyl orange.

APPARATUS. Test tubes, stirring rod, splints.

A. General Properties of Acids.

1. Half fill five clean test tubes with water. To the first add 3 drops of concentrated sulfuric acid, H2SO4; to the second add 3 drops of hydrochloric acid, HC1; to the third add 3 drops of nitric acid, HNO3; to the fourth add 3 drops of acetic acid, HC2H3O2; in the fifth dissolve a crystal of tartaric acid, H2C4H4O6.

2. Dip the clean stirring rod into the dilute sulfuric acid and carefully taste a drop of it. Rinse the mouth with water after tasting. Wash the rod and dip it into the dilute solution of hydrochloric acid and taste a drop of it. Repeat, using nitric, acetic, and tartaric acids. What is the characteristic taste of acids?

3. In each tube place a very small piece of red and of blue litmus paper. What effect have acids on litmus? Empty the tubes and prepare solutions of the acids as in (1). To each tube add a drop of methyl orange. Note result in each

case.

Note: Litmus and methyl orange are called indicators because by their characteristic color reactions they indicate the presence of acids. By giving a different color they may also be used to indicate the presence of bases, as will be shown later.

4. Place about 10 cc. of each acid in separate clean test tubes and add to each (one at a time) a piece of magnesium ribbon about 2 cm. long. Cover the tube with the hand, or a piece of cardboard, for about a minute or until effervescence ceases; then test the gas in the tube with a burning splint. What is the gas? Where does it come from? Write the word-and-symbol equations for the reactions that take place in each case. Do acids dissolve other metals?

5. Write in a vertical column, one under the other, the names and formulas of the five acids you have studied.

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