EXERCISE 68

THE PROPERTIES OF AMMONIUM COMPOUNDS

Apparatus. Evaporating-dish and watch-glass cover; 5 test tubes; burner; hydrogen sulfide generator (Fig. 42).

Materials. Ammonium hydroxide; hydrochloric acid; sodium hydroxide solution; litmus paper (red and blue); 10 g. ferrous sulfide; 0.2 g. ferrous sulfate dissolved in 10 cc. water; ammonium carbonate (R.S.); barium chloride (R. S.); calcium chloride (R. S.); zinc acetate (R. S.).

a. Pour 10 cc. of ammonium hydroxide into evaporatingdish, neutralize with hydrochloric acid, and evaporate to dryness on a water bath (Fig. 33) (?). Note the odor of the residue.

Introduce about one half of the residue (?) into a test tube, add a few drops of sodium hydroxide solution, and heat gently. Note the odor of the evolved gas and its action on a moist strip of red litmus paper (?). This reaction serves as a good test for all ammonium compounds.

Cover the evaporating-dish containing the remainder of the residue with a watch glass and heat gently with a small flame. Note that the solid sublimes; that is, passes directly from the solid form into a vapor which condenses (partly) on the cold surface of the watch glass.

b. Saturate 5 cc. of water (Fig. 42) with hydrogen sulfide and set aside; also saturate 5 cc. of ammonium hydroxide with the gas (?). Add a few drops of each to separate portions of ferrous sulfate solution (?) (ferrous sulfide is soluble in strong acid). In general, what metals will be precipitated by ammonium sulfide and not by hydrogen sulfide ?

c. Add a few drops of ammonium carbonate solution to solutions of compounds of each of the following elements: barium, calcium, zinc (?).

EXERCISE 69

DETECTION OF COMPOUNDS OF THE ALKALI METALS

Recall such reactions of sodium, potassium, and ammonium compounds; also of carbonates, sulfates, nitrates, sulfites, sulfides, chlorides, bromides, iodides, and phosphates as will serve to identify them, and outline a method of procedure in the identification of them. Then ask the instructor for unknown compounds falling within this list and identify them.

EXERCISE 70

THE PREPARATION AND PROPERTIES OF SOAP

Apparatus. Evaporating-dish; ring stand and burner; large beaker; stirring-rod; funnel; small beaker; 4 test tubes.

Materials. Alcohol (R.S.); 5 g. cottonseed oil (or lard); 1 g. sodium hydroxide dissolved in 2 cc. water; hydrochloric acid; magnesium sulfate (R.S.); calcium chloride solution (R. S.); 1 g. sodium chloride dissolved in 5 cc. water; litmus paper (red and blue).

a. Add 10 cc. of alcohol to 5 g. of cottonseed oil in an evaporating-dish. To the resulting mixture add 1 g. of sodium hydroxide dissolved in 2 cc. of water. Evaporate carefully (use small flame and do not let the tip touch the dish), stirring the mixture constantly until the odor of alcohol can no longer be detected. What is formed? What remains in the dish?

b. Add 50 cc. of cold water to the residue in the dish, stir well for a few minutes, and filter. Pour 5 cc. of the filtrate into each of three test tubes. To the first add 2 or 3 drops of hydrochloric acid; to the second add a few drops of a solution of magnesium sulfate. In like manner add a few drops of a solution of calcium chloride to the third.

Note what takes place in each test tube. Why do waters containing calcium and magnesium compounds (hard waters) not lather freely with soap?

c. Add a few drops of sodium chloride solution to 10 cc. of the filtrate obtained in b (?) (p. 417 of text). The soap in the filtrate prepared in b is not in solution but in colloidal suspension (p. 383 of text). The salt causes the precipitation of the colloid (soap).

d. Recall the effect of soap in the formation of emulsions (Exercise 63). What influence has this property upon the cleansing action of soap?

EXERCISE 71

A STUDY OF SOME OF THE COMPOUNDS OF CALCIUM

Apparatus. Evaporating-dish; ring stand and burner; watch glass; small beaker; 2 test tubes; wire gauze; glass plate; platinum

wire for flame test.

Materials. Piece of lime (size of a walnut); bits of marble; hydrochloric acid; ammonium carbonate (R. S.); ammonium hydroxide; disodium phosphate (R. S.); 10 g. plaster of Paris; 0.1 g. each of the chloride or the nitrate of calcium, strontium, and barium.

a. Immerse a piece of calcium oxide (lime) as large as a walnut in a beaker of water for three or four seconds. Repeat (if necessary) until the surface of the lime remains moist for ten seconds after the piece is withdrawn from the water; then place the piece on a watch glass and set the watch glass aside until the end of the period (?). This is a convenient way of preparing calcium hydroxide.

b. Dissolve 1 or 2 g. of marble in hydrochloric acid (R). What does the effervescence indicate? Evaporate the solution to dryness (use the bare flame and evaporate to complete dryness (Fig 33)). What is the composition of the residue? Expose a small piece of it to the air for an hour and account for the results.

Dissolve the remainder of the residue in a little water and divide the liquid into two portions. To the one add a few drops of ammonium carbonate (R); to the other add a few drops of ammonium hydroxide and then of a solution of disodium phosphate. The precipitate is Ca,(PO),

c. Place a piece of marble on a wire gauze and apply a strong heat for about fifteen minutes. When cool, drop the residue into 25 cc. of water and stir. Filter, and test the filtrate with litmus paper. Then blow exhaled air through the filtrate. Explain.

*d. Place on a glass plate a penny which has been rubbed with a drop of oil. Pour over the coin a thick paste prepared by adding water to plaster of Paris. Set the glass plate aside until the paste hardens, then remove the coin and note the result.

e. Try the flame tests for compounds of calcium, of strontium, and of barium (use the chloride or nitrate), as in g, Exercise 65, and note the results.

EXERCISE 72

HARD WATERS AND METHODS FOR SOFTENING THEM

Apparatus. 60-cc. bottle; carbon dioxide generator (Fig. 30); ring stand and burner; funnel; 2 test tubes; small beaker.

Materials. 30 cc. limewater (R. S.); bit of soap dissolved in water; 10 to 15 g. of marble; magnesium sulfate (R. S.); filter paper; 1 g. sodium carbonate dissolved in as little water as possible; hydrochloric acid.

a. Bubble carbon dioxide into 25 cc. of limewater diluted with an equal volume of water. Note that a precipitate forms (R), which gradually dissolves as more of the gas is passed through (?). Add a few drops of a soap solution to 5 cc. of the resulting solution and note the result.

Divide the remainder of the solution into two parts. Gradually boil the one part and note the result. To the other part add a few drops of clear limewater, mix intimately, and note the results. Explain.

b. Shake 1 g. of calcium sulfate with 10 cc. of water in a test tube for two or three minutes; filter, and add to the filtrate 2 or 3 drops of a saturated solution of sodium carbonate (R).

All hard waters contain more or less calcium acid carbonate, calcium sulfate, calcium chloride; also the corresponding compounds of magnesium. (The methods used for removing the calcium compounds likewise serve for removing the magnesium compounds.) How could such waters be softened on a large scale? Waters softened in this way would contain what compounds in solution?

c. Test some hard waters from wells by the above methods.

EXERCISE 73

*SOME ADDITIONAL EXPERIMENTS WITH SOAP

Apparatus. Three 250-cc. bottles; burette or graduated cylinder ; 2 test tubes.

Materials. 1 g. soap dissolved in 100 cc. distilled water; ordinary reagents; 0.5 g. sodium sulfate.

a. The determination of the amount of soap lost by using hard water for washing. Place three 250-cc. bottles on the desk. Into the first pour 100 cc. of hard water (preferably an average sample of the water used in your town or city); into the second pour 100 cc. of distilled (or rain) water; and into the third pour 100 cc. of distilled water containing 0.5 g. of sodium sulfate in solution. Now add to each the soap solution, 1 cc. at a time, and shake the bottle vigorously. Continue adding the soap solution until the lather formed persists for five minutes. Compare the amounts of the soap solution required in each case to produce a permanent lather (?). Does the presence of sodium sulfate prevent the formation of the lather (sodium sulfate is left in waters softened by ordinary methods) (p. 432 of text)?

It will be interesting to make at least a rough approximation of the amount of hard water used yearly in your