ADAPTING ELEMENTARY CHEMISTRY TO GIRLS' INTERESTS A n elementary chemistry course may be adapted to interest girls by the use of illustrations and applications relating to their home life. Suggestions are given for several familiar and interesting applications that help to explain dificult topics. Many of the chemical and physical properties of metals are easier to learn when included under such topics as "Baking Powders," "Softening Water," or "Qualitative Analysis for Ions Important in Foods." The value of a knowledge of chemistry in the everyday life of girls is unquestionable. Every activity of their daily life, their food, clothing, and shelter, involve problems of chemistry if their eyes are opened to the fact. Because of the importance of the subject several courses in chemistry are always required of students of home economics and nursing, and a t least an elementary course is recommended for all girls who wish a well-rounded education. It is a regrettable fact, however, that many girls find elementary chemistry uninteresting and difficult because the subject matter is strange and seems impractical. Through the maze of formulas, equations, and problems, they do not see the applications in their daily life that are so evident to the more experienced person. Since the theoretical matter in chemistry is necessarily new and difficult for most students, every means possible should be used to relate it to their previous experience by the constanf use of familiar illustrations and applications. Many of the industrial applications of chemical principles that are often used as illustrations are as unfanfiliar to the girls as the theoretical topics and only add to the strangeness of the subject. Applications of this type are unnecessary, however, since in the girls' own environment, in their school and home, and especially in their kitchens, their daily experiences furnish countless illustrations of the chemical principles most important to them. It is because chemistry does apply to every phase of home life that borne economics students are required to study it. Wben home applications are used to illustrate difficult topics throughout the course, the theories become simpler and have more meaning, and the students find chemistry interesting and practical from the first. For example, in the study of the metric system, when the liter is compared to a quart and the cubic centimeter to "oue-fifth of a teaspoon," these terms are more real than when expressed simply as "units of volume." The idea of buying dress goods in Paris or candy in Mexico also helps to give the metric units a tangible meaning. The significance of expressing the energy values of foods in calories becomes evident for the first time to many girls when they learn the derivation of the term "calorie." After this explanation they are invariably interested in the action of the calorimeter. 1620
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One may distinguish between physical and chemical changes by comparing the changes in properties that take place in sugar when it is made into fondant or candy, and those that occur when it is burned to carbon. The transformation of chemical energy into heat when wood or coal burns may be compared to the transfer of heat energy in the boiling and freezing of water. In studying mixtures and compounds, baking powders may be shown to be mixtures* fact that may be noted on the labels of their containers. They may be compared to the compound, baking soda, with the chemical name, sodium bicarbonate, different brands of which are alike except in purity and care in preparation. In a similar way sugar and salt may be classed as compounds, while flour, milk, ink, cold creams, face powders, and tooth pastes are undoubtedly mixtures. The subject of solutions is often difficult when only those solutions of unfamiliar compounds on the chemistry shelf are considered. Sugar solutions, however, are familiar in many forms and furnish illustrations of every type of solution. Dilute and concentrated solutions may be compared to sweetened water and thick sirup. Saturated solutions are familiar to every one who has tried to sweeten fruit drinks. The girls know that when the temperature of water is raised the solubility of the sugar is increased. Most of them have prepared supersaturated solutions of sugar in making fudge or sirup. They have probably noted the tendency of the excess solute to precipitate or crystallize from the supersaturated solution, and have learned that either stirring the solution or leaving undissolved sugar on the sides of the vessel hastens the crystalkation. The effect of the concentration of sugar on thqboiling point or freezing point of a solution may have been noted in making candy or in freezing ice aeam. Thus, the concept of molar concentration has an immediate application in the kitchen. The use of alcohol in automobileradiators, and the detection of added water in milk by determining the freezing point are other familiar applications of the effectof molar concentration. In studying the gas laws and the different states of matter many valuable illustrations may be drawn from the kitchen and home. Most girls have observed that water increases in volume when i t is heated in a kettle, and have noted that the metal parts of a stove contract when cooled. Many of them have seen cakes, cream puffs, or popovers, which have risen to many times their original volume in the oven, collapse when they are cooled. All of these facts help to interest them in the relation between the volume of a gas and its temperature. The effect of increased pressure on the volume of a gas may be compared with the effectof pressure on the volume occupied by any loosely packed material such as clothes in a trunk or leaves in a basket. This analogy is also helpful when Boyle's law is explained in terms of the kinetic theory. An explanation of the action of the pressure cooker and the electric
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refrigerator, the effect of an alcohol bath in cooling a patient, the use of dry ice, and the relative humidity in diierent seasons helps to make the study of changes in state simpler as well as more practical. The topic of adds, bases, and salts is always of interest if one recalls the familiar examples in the home. Many of the properties of acids and bases are illustrated in the kitchen. The sour taste of acid fruits and vinegar and the alkaline taste of baking soda are known. Many girls have noticed that grape juice is an indicator like litmus, turning a red color in acid lemonade and blue in alkaline dish water. The relation between the red and blue pigments of flowers may be demonstrated by grinding the petals and testing the extracted color with acids and bases. Some have found their wool dresses spotted with another color from acids or bases and are interested to learn how the original color may be restored by neutralization. The reaction of acids on carbonates is illustrated by the reaction between sour milk and baking soda. It is often helpful to prepare a baking powder from the dry solids, tartaric acid and sodium bicarbonate. The fact that no reaction occurs until water is added demonstrates the necessity of a solvent in order that acids may exhibit their characteristic properties. This fact may then be used to introduce the subject of ionization. Aluminum and iron are affected by acids in the kitchen as well as in the laboratory. The relation between the electrochemical series and the ease of corrosion of metals is both practical and interesting. The action of steam on zinc (galvanized iron) and the action of alkalies on both aluminum and zinc is a new and interesting idea to girls who have had to clean these metals. Because aluminum is above iron in the e. m. f. series some of the iron present in foods cooked in aluminum utensils may be displaced and precipitated by the aluminum, thus substituting a useless mineral in the food in place of an important one. The f a d that silver and gold .are not easily corroded may be deduced from a study of the e. m. f. series. This inactivity makes them valuable as metals, and explains their discovery and use early in history. Bases are less familiar than acids to the average student, though most of them have used either ammonia water or lye. The fact that alkaline solutions tend to destroy protein matter such as wool, silk, or their own skin is especially interesting when they learn that most washing powders are alkaline in reaction. The reaction of bases with fat to form soap explains why alkaline solutions are useful for cleaning greasy articles. The topic of hydrolysis shows why washing powders, usually mixtures of sodium carbonate and borax, are alkaline, and why even baking soda, an acid salt, has a basic reaction. Many girls have used ammonia water or borax in cleaning, and have used baking soda to neutralize the acid in sour fruit, or possibly in a bee sting.
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ELEMENTARY CHEMISTRY FOR GIRLS
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The concept of hydrogen-ion concentration is always most easily introduced in terms of the "sourness," possibly by comparing the taste of various fruits, or of hydrochloric and acetic acids. It is noted that it is the hydrogen ions that cause the sour taste and, that just as the saltiness of one solution depends on its concentration of salt, and the sweetness of another solution depends on its concentration of sugar, the sourness of an acid depends on the hydrogen-ion concentration. The effect of the alkalinity or low hydrogenion concentration of washing powders and soaps on protein has been suggested. Girls with experience in cooking are interested in the d e c t of the pH value of a mixture of baking soda and sour milk, or of baking powders, on the disintegration of the protein matter in doughs and batters. It may be noted that the pH value of tomato soup, gelatin desserts, and jelly affects both the texture and taste of the product. It is also interesting to note that the gastric juice, the intestinal contents, and the blood all have optimum pH values which must be kept constant by the action of buffers. It is in the study of the colloidal state that students become most interested in the practical applications of chemistry to their daily life. Learning the true nature of pearls and opals, of fog and smoke, and of foods and their own bodies adds romance to the practical. The laws that govern crystal growth find an application in making creamy fondant or in freezing ice cream. Protective colloids are used in marshmallows, divinity candy, and ice cream. The principle of adsorption is illustrated in the use of fine powders to remove stains and in the precipitation of muddy coffee by egg white. The idea of precipitating fog or smoke by electrical methods always excites interest and gives the other applications of electrophoresis more meaning. The absorption of food in the intestines is the most important illustration of dialysis. The effect of pH value on the hydration of protein is important in cake batters, bread doughs, omelets, gelatin dishes, jellies, and meats, and is also an explanation of various pains in the body ranging from bee stings to nephritis. The properties of emulsions and the action of emulsifying agents find practical application in the preparation of mayonnaise and French dressing as well as in gravies and rich pastries. The action of soap in cleaning is enlightening to many. The similarity in the separation of sour milk into curds and whey, the sweating of jellies, the curdling of custards, and the aging of the body is also interesting. While the use of illustrations of this type aids materially in making an elementary chemistry course interesting and useful to girls, i t is also helpful to adapt the subject matter to their needs as far as possible Many of the topics that are often emphasized in inorganic chemistry, such as the preparation, properties, and commercial uses of each of the several important inorganic compounds, and the history and metallurgy of each separate element, have a minimum of interest to girls. It is often profitable to neglect these topics in favor of certain theoretical subjects that give the
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student a better appreciation of science and its importance in their own daily life, and a t the same time a better preparation for the advanced courses. Many of the important reactions of inorganic compounds may be introduced profitably in a complete study of certain topics on which these reactions find application. For example, the topics "Baking Powders" and "Softening Waters" seem more interesting and useful from a student's viewpoint than "The Calcium Family" and "The Sodium Family," although many of the same reactions are included in both types of subjects. A simple method of analyzing an unknown mixture for the ions that are most important in our foods and bodies will include many of the most important reactions of these elements and will teach them in a way that is both interesting and helpful for retention. When girls become interested in the elementary chemistry course and realize that each topic they study opens to them new vistas of learning that relate to every phase of their life, they are willing and anxious to master the formulas, problems, and new theories in anticipation of understanding more of the life and experiences about them. Memorizing valence and studying the structure of the atom and the arrangement of the elements in the periodic table are not too difficult to be worth while when the girls have reason to believe that they will soon be able to apply them. In this way the proper choice of illustrations and applications makes it possible to teach more of the actual theory of chemistry and at the same time increases its usefulness and interest.
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