MATERIALS.

EXPERIMENT 4

Physical and Chemical Changes

Granulated cane sugar.

APPARATUS. Beaker, test tube, mortar and pestle, Bunsen burner, ring stand, wire screen, test tube holder.

Note to teacher: It is convenient to measure out the proper amount of material on squares of paper on the distributing table ready for the students. This saves a great deal of time and material.

A. How Sugar May Be Changed.

1. Take a clean dry test tube and obtain about 10 grams of sugar from the distributing table. (NOTE: Be careful not to spill material on the distributing table — if you do, clean it up. Hold the stopper of the bottle in your hand and replace it when you are through.) Carefully note the properties of the sugar, its crystalline form, its hardness, color, and taste. How could you distinguish it from table salt? What then is its most characteristic property?

2. Put about half of your sugar in a clean mortar and grind it till it is a powder. Taste it. Is it still sugar? Has its characteristic property been changed by grinding? This is a physical change, because the composition of the substance is unchanged, as is shown by the fact that no change in the characteristic properties has occurred.

3. Fill your beaker one fourth full of water and add the powdered sugar from the mortar. Stir with your stirring rod until the sugar is dissolved. Taste the solution. Has the sugar been destroyed? What has happened to it? This is a physical change.

4. Heat the remainder of the sugar in a dry test tube until it stops smoking. Note every change carefully. When

no further change takes place, cool the tube, break it, and examine the substance remaining in the tube. What is its form, its hardness, color, and taste? Will it dissolve in water? Try it. Has the substance any properties of sugar? This is a chemical change, because the composition is changed and a new substance is formed, having new properties.

B. How Other Substances May Be Changed.

Tear a piece of paper into bits. Is the change physical or chemical? Why? Burn a piece of paper. Describe the change. Is it a physical or a chemical change?

C. Some Changes We See Every Day.

Are the following changes physical, or chemical, or both? Give a reason for your answer in each case. 1. The souring of milk. 2. Making a batter from flour, milk, and eggs. 3. Baking bread. 4. Making candy. 5. Beating an egg. 6. Boiling an egg. 7. Freezing cream in making ice cream. 8. Tarnishing of copper.

Note: Have your notes signed.

EXPERIMENT 5

Elements, Compounds, Mixtures

MATERIALS. Sulfur, about 5-gram portions, magnesium ribbon, 3 cm. strips, mixture of equal parts powdered sugar and sulfur, 10-gram portions, Shaker Salt 10-gram portions.

APPARATUS. Evaporating dish, forceps, Bunsen burner, filter paper, funnel, stirring rod, two beakers.

Note to teacher: Before entering the laboratory, show how to fold a filter and the correct method of filtering.

Note to student: Take careful notes and have them signed before leaving laboratory.

A. Elements.

1. Obtain 5 grams of sulfur in a test tube. Examine it carefully. What are its chief physical properties, i.e. color, odor, taste. Try to dissolve a little in a test tube half full of water. Is it soluble in water? Is sulfur a metallic or a non-metallic element? Can you find in the Appendix the names of three common non-metallic elements?

2. Obtain a piece of magnesium ribbon about 3 cm. long. Notice its color and weight, its luster, and its flexibility. Is it a metallic or a non-metallic element? Give the names of three common metals and give a use for each.

3. Repeat 2, using aluminum instead of magnesium.

4. Now tell in your own words what an element is.

B. Compounds.

1. Place a little sulfur about the size of a pea in your evaporating dish. Heat the sulfur by means of the burner flame till it burns. Very carefully note the odor. Is this a physical or chemical change? We have noted the physical properties of sulfur in A, 1. We have now observed one chemical property of sulfur. What is it? The gas that is formed when sulfur is burned is sulfur dioxide. It is a compound.

2. By means of the iron forceps hold the piece of magnesium ribbon in the flame. Result? What is formed? Has the new compound any of the properties of the metal magnesium or the gas oxygen from which it was formed? In general, what is formed when an element burns in the air? Give a chemical property of magnesium.

3. Repeat 2, using aluminum instead of magnesium. What is formed? Give a chemical property of aluminum.

4. Is sugar an element or a compound? How did you prove this in the preceding experiment? What is one element in it? Consult the textbook and find out the other elements in sugar. What are the elements in table salt (sodium chloride)? in water?

5. What is a compound?

C. Mixtures.

1. A well-known remedy for sore throat consists of a mixture of equal parts of sulfur and powdered sugar. Obtain from the instructor about ten grams of this remedy in your beaker. Fill the beaker half full of water and boil for about one minute, stirring occasionally. Which constituent of the remedy will dissolve? Which one will not? Remove the beaker from the ring stand and filter. The solid will remain on the paper and the liquid will pass through it.

To prepare a filter paper fold it once and then again at right angles to the straight edge. Open the paper as a cone, with a triple layer of paper on one side and a single layer on the other. Place it in the funnel and moisten it well with water. The paper should not come to the top of the funnel. Place the funnel in the ring of the ring stand. Place the other beaker under the funnel. Adjust the ring so that the stem of the funnel extends into the beaker about one inch. To pour the liquid from the beaker into the funnel without spilling it hold the glass rod lightly against the rim of the beaker. The liquid will flow down the rod. The liquid that goes through the filter paper is called the filtrate.

Taste the filtrate. Where is the sugar? Where is the sulfur? If a mixture consists of two substances, one soluble

in water and one insoluble, what is the general method of separating them?

2. "Shaker Salt" is pure sodium chloride (table salt) to which has been added a little starch to keep it dry. Starch is not soluble in water. Obtain ten grams of "Shaker Salt." Stir it into half a beaker of cold water. Is starch

present?

3. Now define a mixture clearly.

II. OXYGEN AND HYDROGEN

EXPERIMENT 6

Ways of Freeing and Collecting Oxygen

MATERIALS. Powdered potassium chlorate 8-gram portions, splints (about the size of a match and 7 inches long), powdered manganese dioxide 2-gram portions.

APPARATUS. Bunsen burner, test tubes, gas bottles, pneumatic trough, glass plates.

A. How to Obtain Oxygen.

1. Oxygen is the gas in the air which makes a fire burn. The air would be an excellent source of oxygen if it did not have so much nitrogen mixed with it. It is difficult to remove the nitrogen and leave the oxygen.

2. The compound potassium chlorate, KClO3, is the most convenient source of oxygen. Obtain 8 grams of powdered potassium chlorate and 2 grams of manganese dioxide. Divide the potassium chlorate into two equal parts. Put one part (4 grams) in a clean, dry test tube. Mix the other part (4 grams) on a piece of paper with 2 grams of manganese dioxide (half as much), using the stirring rod. Then put it into a clean, dry test tube of the same size as the first.