JOHNNY INVESTIGATES CHARLES H. STONE Vermont Junior College, Montpelier, ~ e r m o n i
OBSERVATIONS made in chemistry classes in various that the effect of heat on the carbonates of the alkali secondary schools in several states lead the writer to the metals he investigated, with the added suggestion that opinion that opportunities for original thought, in- acid he applied to these carbonates both before and dividual experimentation, and investigation of simple after heating. Johnny finds that hefore heating, problems are minimized by the procedures indicated these carbonates, like all others, sizzle when acid is below which are common everywhere: applied, and they also sizzle after strong heating. So, ( a ) The teacher discusses with the class the topic apparently, they are not changed by heat. Whence may issue this general statement: "With the exception in hand. of the alkali carbonates, all carbonates are decomposed (b) The textbook gives full information q to the into the oxide of the metal and carbon dioxide." He preparation and properties of the element or compound may observe that the resulting oxides are often of a under immediate discussion. different color from that of the original carbonate. (c) As a consequence, the pupil goes to the labora- I s the ahove general statement found in the text or tory knowing already what is going to happen in the preparation of hydrogen, ammonia, or sulfur dioxide. manual you are using? The only instance is that for He thus becomes a verifier of facts that have already the preparation of lime. It must hs obvious that'it is better to have in mind been brought to his attention. True, he acquires one general statement covering a considerable number through repeated use certain valuable manipulative of related cases than it is to try to remember a number skills, but he rarely discovers anything not set forth in of individual instances. the text or in the discussions by the teacher. He folHere are some other experiments calling for student lows the instructions in the manual, but when does he initiative which may he used as occasion offers: stand on his own feet and, thiough individual emerimentation, find the answer to s&m simple problem 1. P~operties. The student is given a small lump of roll sulfur with the suggestion: "Find out all you can about this elenot set forth in the text or manual? ment." Now suppose the pupil is given some simple problem (a) What three obvious properties are noted at once? which is not familiar and is expected to work out for (b) Put the lump in a mortar and hit it lightly with the pestle. himself the proper answer. For example: "What is the Is sulfur brittle or tough? (c) Has one of the small pieces any taste? reaction between warm dilute nitric acid and the simple (d) Will one of these pieces held in the tweezers or tongs burn oxides of the common metals?" Johnny investigatks if held in the ilame of the bunsen burner for a moment? and finds that common oxides such as those of lead, (e) If so, is there a color to the flame, or an odor? copper, cadmium, nickel, and cobalt dissolve readily V) Reduce some of the pieces to a fine powder in a mortar. in the acid, and hence a general statement may be Add a little of this powder to each of three test tubcontaining: 5 ml. of cold water, 5 d of hot water, 5 made: "The simple oxides of the common metals ml. of cold carbon di6ulfide. Results? are all soluble in nitric acid." Is this proposition (g) Grind in a mortar two grams copper powder and one gram set forth in the text or manual in use? Or again:. powdered sulfur. Put into a test tube and heat. Re"What is the effect of heat on the carbonates of the sults? Summarize your findinas common metals?" Johnnv investieates and, 6nds - from the ahove. that the carbonates of the common metals are all z. ~ i r e d u n k ~ f e z e ~ e ~ t s (a) What arc three ohvious properties of mercury: three of decomposed into the oxide with liberation of carbon iodine? dioxide. He may discover that it is much more difficult (b) Put a globule of mercury of the size of a pea into a clean dry to decompose the carbonates of barium and calcium mortar. Add a little iodine and grind. Continue with than those of lead and copper. The alkaline earth successive small portions of iodine, avoiding an excess, carbonates are more stable. The teacher may suggest until the last tiny globule of mercury disappears.
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NOVEMBER, 1947
If a purple vapor rises from the product how is tbat to be explained? What is the effect of heat on iodine7 Is your product warm? (d) "When two elements comb'me to form a compound, the elements lose their original properties and the substance formed has properties unlike either of the original el* ments." Is this statement true or false? Does it . appear in either text or manual7 3. True or false statements "When hydrogen is passed over hot copper oxide copper is formed. (See experiment in manual.) This is because hydrogen hss a great attraction for capper." True or false? "When dilute sulfuric soid and zinc react, hydrogen is formed. The acid drives the hydrogen out of the zinc, doesn't it? True or false? "Any base will neutraliae any acid." True or false? 4. Reoctia of mides with acids. Lead oxide and copper oxide will dissolve readily in warm dilute nitric acid. (See earlier statement.) Will these two oxides also dissolve readily in warm dilute sulfuric acid? Try it. Results and explanation? 6. A m m h (a) What are the two components in every ammonium salt? (6) why is it necessary to use a base with such a salt to liberste ammonia? (c) Could an soid be used in place'of the base? Why? (d) Cut a cylinder of wood charcoal about '/, inch long and of siee as to slide easily up and down in a 6.inCh test tube. Boil in the tube 5 ml. of eonc. ammonium hydroxide, pour out the liquid, slip the charcoal cylinder down in a up into the tube and stand the tube small beaker containing mercury. What happens? Why7 More mercury may be added if neoessary. Raise the tube when action is over and let the mercury run out. 'Remove the obarcoal and smell it: (e) Why is charcoal used in gas masks? If) Chercoal and sulfur are nonmetals. would sulfur behave similarly? 6. Sodium nitrate; oxidizing action (a) Compute the percentage of olrygen in water and in sadium nitrrtte. (5) From your figures, which substance w d d be the better supporter of combustion? (c) Will hot water support the combustion of wood? (d) Will hot sodium nitrate support the combustion of wood? Put 5 g. of the nitrate into a dry tube sfpported verti~~~tthe tube cally. Have a' band a wood from the side until the nitrate melts. Set the burner to one side and test for oxygen. Results? (4 Drop the splint with spark into the melted nitrate. &sults? (Observe from the side.) ~f. (f) Why does the compound with the smaller oxygen prove to be the better supporter of combustion7 (Do not drop any powdered combustible into the hot nitrate.) 7. Stability of simple oxides (a) Heat about two grams mercuric oxide in a tube. Test for oxygen. (b) Heat about two grams of copper oxidein a tube. ~ e sfor t oxygen. (c) Scrape out the material onto a sheet of paper.
569 (c) How do you explain the daerence in results?
(d) Is mercury above or below copper in the displacement series? Conelusion. 8. Hydrated and anhydrous sol& (a) What is the color of crystauiaed copper chloride? (b) Put five grams of this salt into a dry test-tube and clamp level with open end slightly lower. Hest moderately using a small flame until the change is complete. Dry out the tube with rolled filter paper. What is the color of the product? (Too much heat will spoil this sxperiment.) (c) What is the c m e of the color in crystallized copper chloride? (d) In an ewporating dish heat five grams of powdered copper sulfate crystals until the blue color is entirely gone. (e) Put a smdl quantity of the resulting powder on the palm of the hand and add ONE drop of cold water. What two results? (f) Exphin each result. 9. An aduenture in catalysis (a) Will manganese dioxide yield oxygen if moderately heated7 Try. (b) Will potassium chlorate yield oxygen if strongly heated7 Try. (c) What happens when the hot dioxide is added to the fused potassium ehlorate after the heat of the burner is removed? (Spark test.) (d) What proved in this 10. Investigation of a series of reaction8 slaking with copper mrbonate (a) What is Of the (b) Put ten grams of the carbonate powder into an evaporating dish and stir in warm dilute nitric acid in successive small amounts till the action is complete. Whet h a p pens? Equation? (c) Filter. Color of filtrate? (d) Evaporate this filtrate to dryness. Result7 Equation? (e) Transfer this last result to a dry tegt tube clamped level. Using a g l q L tube, psss illuminating gas aver the product and ignite the gas escaping s t mouth of tube. (fl Heat the product moderately in the tube until action ia complete. Result? Equation (assumingthat hydrogen is a component of the illuminatinggas). (9) What shorter method could be used to obtain this final result7 .. .,
~t is not suggested that experimen& as those above should displace those in the manual. Teachers are obliged to follow the requirements of the colleg& that require a certain number of experiments performed from the manual in use. &$, it seems that op~ o r t u n i bmay ' be found here and-there with the better students to do some experimental work of the investigative kind. It is interesting to note the reaction of such students to this sort of work, They seem to finding out the amwers for themselves; it gives them a' sense of confidence in their own ability to solve simple problems.
