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  Lionel Chem-Lab - Chapter 13

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NOTE:  This book was published in 1942 as a manual to accompany several Lionel Chemistry sets of the time.  While some of the experiments and activities here may be safely done as written, a number of them use chemicals and methods no longer considered safe.  In addition, much of the information contained in this book about chemistry and other subjects is outdated and some of it is inaccurate.  Therefore, this book is probably best appreciated for its historical value rather than as a source for current information and good experiments.  If you try anything here, please understand that you do so at your own risk.  See our Terms of Use.
Pages 159 - 162

CHAPTER XIII

THE ALKALI METALS: SODIUM AND POTASSIUM

Sodium and potassium are commonly called the alkali metals because their hydroxides are strong bases or alkalis. Although there are five metals in this group, only sodium and potassium are of commercial importance and we shall quickly pass over the other three. Ordinarily we think of metals as being hard substances and comparatively inactive, but sodium and potassium refute this common impression. They are soft enough to be cut with a knife, light enough to float on water, and they melt at a lower temperature than that at which water boils. Both sodium and potassium combine so readily with water and oxygen in the air, and so much heat is evolved, that the chemist has to keep them immersed in kerosene.

Because they are so active, sodium and potassium do not occur in the native state, but combined with other elements they exist in dozens of common, well-known compounds. Sodium chloride (common table salt), sodium nitrate, and sodium tetraborate (borax) are examples of some of the more important sodium compounds. Among the potassium compounds, potassium chloride, potassium nitrate, potassium carbonate (potash) and feldspar are the principal ones.

SODIUM COMPOUNDS

The chemical name for ordinary table salt is sodium chloride, and although we are inclined to think of it only as a seasoning for our food, the fact remains that it has many other important uses. Because it is so easily obtainable, salt is used in the preparation of practically all the sodium and chlorine compounds, including soda, glass, soap, chlorine, hydrochloric acid and bleaching powder.

Sodium hydroxide, an important base manufactured in large quantities, is used in many products including soap, petroleum, dyes and rayon. Lye and caustic soda are other names for sodium hydroxide.

EXPERIMENT No. 344 Preparation Of Sodium Hydroxide

(CL-11, CL-22, CL-33, CL-44, CL-55, CL-66, CL-77)

APPARATUS: Sodium carbonate, calcium oxide, three test tubes.

PROCEDURE: Dissolve three measures of sodium carbonate in a

159


160 THE ALKALI METALS

test tube half full of water. Dissolve two measures of calcium oxide in another test tube containing the same amount of water. Mix the two solutions thoroughly. Filter into a clean test tube. The filtrate is sodium hydroxide.

EXPERIMENT No. 345 A Test For Sodium Hydroxide

(GL-11, CL-22, CL-33, CL-44, CL-55, CL-66, CL-77)

APPARATUS: Calcium oxide, sodium carbonate, test tubes, red litmus paper.

PROCEDURE: Prepare a solution of sodium hydroxide as described in the preceding experiment. Drop a piece of moistened red litmus paper into the test tube. Sodium hydroxide being a base will change
red litmus paper blue.

Sodium hydroxide dissolves animal fibers of wool and silk, but has little, if any, effect on cotton and linen which are vegetable fibers. Because of this, it is a test used to determine whether or not a fabric is made from wool or cotton.

Sodium carbonate (washing soda) and sodium bicarbonate (baking soda) are important sodium compounds. They are both produced by the Solvay Process, in which the bicarbonate is formed simultaneously with the carbonate.

The principal uses of sodium carbonate are in the making of soap products and glass. Sodium bicarbonate, or ordinary white baking soda, can be prepared by bubbling carbon dioxide into a saturated solution of sodium carbonate.

EXPERIMENT No. 346 Preparation Of Sodium Bicarbonate

(CL-77)

APPARATUS: Erlenmeyer flask, test tubes, sodium chloride, household ammonia, alcohol, filter paper, funnel, gas generator, delivery tube and beaker.

PROCEDURE: Place one test tube full of water and two tablespoons of sodium chloride in the Erlenmeyer flask. Stopper the flask and shake thoroughly for two or three minutes. Allow the excess salt to settle. Then decant one quarter test tube of solution into a dry test tube and add one half test tube of household ammonia and mix thoroughly. Add one quarter test tube of alcohol and mix again. Prepare carbon dioxide gas as described in Experiment No. 151. Attach delivery tube of the gas generator so that the end of the tube reaches well below the surface of the solution in the test tube. Allow the carbon dioxide gas to bubble through the solution while shaking the test tube. Continue adding carbon dioxide until no more bubbles appear. Within ten to fifteen minutes, a precipitate will form. Filter and add one quarter test tube of alcohol to the precipitate. Wash the precipitate with water. Remove precipitate from filter paper and spread it on a clean paper towel to dry.

LIONEL CHEM-LAB 161

SUMMARY: Sodium chloride, in the presence of ammonium hydroxide, forms sodium hydroxide, ammonia gas and water. Sodium hydroxide absorbs the carbon dioxide gas to form sodium bicarbonate. Alcohol does not react chemically with any of the above compounds, but is used in this experiment to change the dissolving capacity of water making sodium bicarbonate less soluble in the mixed solvent than in water.

EXPERIMENT No. 347 Hydrolysis Of Sodium Bicarbonate

(CL-33, CL-44, CL-55, CL-66, CL-77)

APPARATUS: Sodium bicarbonate, phenolphthalein, test tube, candle.

PROCEDURE: Place one measure of sodium bicarbonate and one drop of phenolphthalein in a test tube one quarter full of water. Shake test tube and note the color of solution. Heat solution to boiling for a few minutes. Note the change of color due to the hydrolysis of sodium bicarbonate.

When sodium bicarbonate and hydrochloric acid are mixed in the proper proportions, carbon dioxide gas is liberated.

Because baking soda generates carbon dioxide gas under certain conditions, it is used in bakeries to "raise" bread. It is also employed to make carbon dioxide gas in certain types of fire extinguishers.

POTASSIUM COMPOUNDS

The compounds of potassium are quite like the corresponding sodium compounds but are more active. Potassium is important to plant life, and is thus used principally to make fertilizers.

EXPERIMENT No. 348 Preparation Of Potassium Hydroxide

(CL-44, CL-55, CL-66, CL-77)

APPARATUS: Potassium chloride, calcium oxide, sodium carbonate, test tubes.

PROCEDURE: Prepare a solution of sodium hydroxide as explained in Experiment 344. Dissolve two measures of potassium chloride in another test tube one quarter filled with water. Mix the two solutions and add one drop of phenolphthalein.

SUMMARY: Sodium hydroxide reacts with potassium chloride to form sodium chloride and potassium hydroxide which colors the solution red.

EXPERIMENT No. 349 Preparation Of Potassium Carbonate

(CL-33, CL-44, CL-55, CL-66, CL-77)

APPARATUS: Phenolphthalein, wood ash, test tube, candle, drinking glass.


162 THE ALKALI METALS

PROCEDURE: Place six teaspoonsfuls of wood ash in a glass half full of water. Mix thoroughly with a stirring rod then allow to stand for three minutes. Filter one quarter test tube of the material and add one drop of phenolphthalein solution.

SUMMARY: Wood ash has potassium carbonate as one of its constituents. Adding phenolphthalein solution results in the pink color due to the basic properties of potassium carbonate.

EXPERIMENT No. 350 Preparation Of Potassium Acid Tartrate

(CL-44, CL-55, CL-66, CL-77)

APPARATUS: Tartaric acid, potassium chloride, test tubes.

PROCEDURE: Dissolve four measures of tartaric acid in a test tube one quarter full of water. Dissolve three measures of potassium chloride in another test tube containing the same amount of water. Add the tartaric, acid to the potassium chloride and note the white crystalline precipitate of potassium acid tartrate.

EXPERIMENT No. 351 Identification Of Potassium

(CL-66, CL-77)

APPARATUS: Nichrome wire, potassium chloride, alcohol lamp.

PROCEDURE: Place one measure of potassium chloride on a clean sheet of paper. Moisten the nichrome wire and dip it into the potassium chloride. Place the wire in the non-luminous part of the flame. Potassium compounds color the non-luminous flame violet. (Sodium may obscure the violet color but by viewing the flame through cobalt blue glass the violet color can be seen easily).
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