Apparatus. --- EXPERIMENT XLII. SULPHUR DIOXIDE. 100 c.c. flask, ring stand, wire gauze, stopper and delivery tube, 2 collecting bottles, test tubes, beaker, evaporating dish. Materials. Granulated copper, concentrated sulphuric acid, red flower, red cheese cloth, crystals of cupric sulphate, dilute sulphuric acid, sodium hydroxide solution, litmus paper, concentrated nitric acid, potassium permanganate and potassium dichromate solutions. a. In a 100 c.c. flask put about 5 grams copper and add 25 c.c. concentrated sulphuric acid. Support the flask in a ring stand, upon wire gauze, and attach a stopper and a doubly bent delivery tube reaching almost to the table. b. Heat the flask carefully. When brisk effervescence begins, moderate the heat. Collect 2 bottles of the gas as you did chlorine in Experiment XXI, b. Tell when each bottle is full by the odor. Stopper the bottles. Collect, also, a test tube of the gas and put it, mouth down, into a beaker of water. Explain the result. Wave a little of the escaping gas toward the nose. Odor? The gas is sulphur dioxide, SO2. c. Put the end of the delivery tube just at the surface of 10 c.c. water in a test tube. When the gas is coming off freely, raise the test tube about 1 cm. What evidence is there that the gas is dissolving? Lower the test tube to its former position and keep it there five minutes. Then SULPHUR DIOXIDE. 65 remove the delivery tube from the water, extinguish the flame, and let the generating flask cool in position, out of contact with the wire gauze. Stopper the test tube containing the solution of the gas, and keep it. d. Into one bottle of sulphur dioxide gas put a few petals of some red flower, e. g., a carnation; also a small piece of wet, red cloth such as you used with chlorine in Experiment XXI, e. Results? Test the action of sulphur dioxide upon blue litmus paper. Result? e. To the second bottle of sulphur dioxide add 4 drops of concentrated nitric acid, stopper the bottle, and shake it. Results? Add 5 c.c. water, stopper once more, shake, and pour the liquid into a test tube. Save this for Experiment XLIV, c. f. Note the taste of a drop of the sulphur dioxide solution made in c. What is the action of 1 c.c. of it upon 1 c.c. potassium permanganate solution (KMnO1)? Repeat with potassium dichromate solution instead of potassium permanganate. Result? Sulphur dioxide solution contains sulphurous acid, H2SO3. g. Neutralize the remainder of the sulphurous acid in an evaporating dish with 10 per cent sodium hydroxide solution and evaporate to dryness. The resulting substance is sodium sulphite, Na2SO3. Describe it. Complete the equation, h. Treat the sodium sulphite in a test tube with a little dilute sulphuric acid, and warm. Note the odor. The sulphite is decomposed by the acid thus: Na2SO3+H2SO4 Na2SO4+H2SO3 (i. e., SO2+H2O). i. When the generating flask is cold, add to it 25 c.c. water, shake carefully, and heat the flask cautiously over wire gauze. Filter the resulting liquid. What is the color of the filtrate? Concentrate it to about 15 c.c., and let it cool. Result? Compare the product with blue vitriol, CuSO4. 5 H2O. Complete the equation, Cu+H2SO4 EXPERIMENT XLIII. SULPHURIC ACID. Apparatus. File or blue paraffin pencil, test tube, beaker, balances. Materials. Concentrated sulphuric acid, sugar, cotton, cloth, paper, splinter. a. By means of a file or a blue paraffin pencil mark off about 10 c.c. on a clean, dry test tube, set the tube in a clean beaker, and get the weight of both test tube and beaker together. Now fill the tube up to the mark with concentrated sulphuric acid, wipe off any acid adhering to the mouth of the test tube, and get the weight of acid beaker + test tube. Return the acid to the bottle, rinse the test tube, and dry it on the outside. Then fill the tube up to the mark with water, and get the weight of water + beaker + test, tube. SULPHATES. Record your results thus: Wt. of test tube + beaker + sulphuric acid Wt. of test tube + beaker ... Wt. of sulphuric acid taken Wt. of test tube + beaker + water .. Wt. of water taken From the results calculate the specific gravity of your sulphuric acid. b. Heat one drop-no more - of concentrated sulphuric acid in an evaporating dish over wire gauze. Result? c. Put into a test tube a splinter of wood and add 5 c.c. concentrated sulphuric acid. Let stand fifteen minutes. Try the effect of a drop of concentrated sulphuric acid on paper; upon cotton cloth. Wait for the result if it is not immediate. Results. d. Into a small beaker put 10 grams sugar and 5 c.c. water, and stir thoroughly. Now add 10 c.c. concentrated sulphuric acid. Results? Describe the product. barium chloride, cupric sulphate, sodium sulphate; dilute hydrochloric acid; liquid from Experiment XLII, e. a. To 10 c.c. water in a test tube add 1 c.c. concentrated sulphuric acid. Result? Heat the diluted acid to boiling, and add 5 c.c. barium chloride solution, BaCl2. Result? The precipitated substance is barium sulphate, BaSO4. If the other product is hydrochloric acid, write the equation. Let the precipitate settle, pour off the supernatant liquid, and add 10 c.c. dilute hydrochloric acid to the precipitate. Does the precipitate dissolve? b. Repeat a, using instead of dilute sulphuric acid 5 c.c. of a solution of cupric sulphate, CuSO4. Results? Equation? Repeat again, using 5 c.c. of sodium sulphate solution, Na2SO4, with 5 c.c. barium chloride solution. Result? Equation? Note.--In general, if a solution gives with barium chloride solution a white precipitate insoluble in dilute hydrochloric acid, we are reasonably sure that the unknown solution contains sulphuric acid or a sulphate. c. Treat the liquid obtained in Experiment XLII, e, with barium chloride solution. Result? What effect did nitric acid have upon the sulphur dioxide? Complete the equation, SO2+O+H2O. |