Amylase + starch. Dem. 670 - Journal of Chemical Education (ACS

Amylase + starch. Dem. 670. Robert Barnard. J. Chem. Educ. , 1969, 46 (9), p A634. DOI: 10.1021/ed046pA634.4. Publication Date: September 1969 ...
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+ Cellulose

Procedure: Taking care not to wet the neck of the balloon, squirt a medicine dropperful of water into a rubber balloon. Push a lump of CaCI (0.5 cm3, no larger, CARE)into the neck, and tie shut with thread. Project. Now dump the lump into the water inside the balloon. Throw expanded balloon into a Bunsen flame.

Materials: Soln. A : 5 g soluble cellulose in 100 ml water. S o h . B : light brown solution of iodine in water. Alpha-amylase, cell H-3, stirrer.

Observation: As CzHz is generated, the balloon is filled with gas. Explodes in air when thrown into Bunsen flame.

Procedure: Half-fill two culture tubes with A . Add l g alpha-amylase to tube 2. After 30 min, project in H-3. Add a dropperful of B to each tube.




Reactions: CaCz 2H2O 2C2H2 502 4COI 2H20






+ C2H2;

J. Chem. Educ., 6,2011 (1932).

Dem. 669-Amylase

Experiment developed by Robert Barnard. To show: Cellulose fermented to starch by amylase.

Observations: Tube 1: no coloration, showing starch is not present. Tube 2: hlue coloration due to starch formed from cellulose by fermentation.

C. Ring Compounds

D. Natural Products

Dern. 670--Amylase

+ Starch

Experiment developed by Robert Barnard. Dem. 667-Formic

Acid Swelling Proteins

To' show: How formic acid iu the sting of an insect causes swelling of proteins. Materials: Gelatin, formic acid, hypodermic syringe and needle, phenolphthalein indicator solution; NaOHaq, hotplate, 250 ml beaker, stirrer, H-3. Procedure: Dissolve 5 g gelatin in 100 ml boiling water; to it add four drops indicator a single drop of NaOH to turn it red. Pour into two culture tubes. Let gel. Project in H-3. Plunge the hypodermic needle into the center of each gel, injecting one drop HC1 into tube 1 and one drop of HCOOH into tube Z. Project for 15 min.


Observations: Both acids decolorize the red indicator. After some minutes the channel containing the formic acid begins to swell. Dem. 668-Distillation

To show: Starch fermented to sugar by an enzyme, alpha-amylase. Materials: Soln. A: 5 g starch dissolved in boiling water, cooled to room temperature (important) and filtered if necessary to give a clear solution. Soln. B: a light-brown solution of iodine in water. Alphsr amylase, cell H-3. Procedure: Half-fill two culture tubes with A . Add l g alpha-amylase to tube 2 . After 30 min, project in H-3. Add a dropperful of B to each cell. Observations: Tube 1: deep iodine-blue showing presence of starch. Tube 2: pale hlue, showing starch has disappeared, the amylase fermenting it to sugar.

of Wood

Experiment dezleloped by August J . Colo. To show: Products from the distillation of wood. Materials: A 13 X 100 mm test tube quarterful of soft wood chips; one-hole rubber stopper carrying a l/a-inch copper delivery tube in through a 2-hole stopper in an empty 2-02 square glass bottle; an exit tube of glass or copper leading to a second 2-hole stopper in a 2-02 square glass bottle quarterful of dry CaO; an exit tube of copper or 5 mm glass tubing. Procedure: Project with the test tube of dry wood chips over an alcohol burner. Heat as hot as possible. I n a few minutes gas will issue from the exit tube in the end bottle, and can be ignited there. Hold a matchhead in this flame. Observations: Wood-tars collect in the empty bottle. I n the second bottle pyroligneous acids from the wood are absorbed by the lime. The exit gas burns and can be made visible on the projection screen by the match-head igniting. Note: Hard coal requires a much higher temperature than is provided by the alcohol burner. A634


Journal of Chemicol Educafion

Dern. 671-Titration

of Vitamin-C with Iodine

To show: Vitamin C content of orange juice treated with iodine and back-titrated with thiosulfate. kc-COH=COH-CH-CHOH-CHSOH + In O=C-COHI-COHI-CH-CHOH-H


Materials: Orange juice, 0.01 N iodine-aq, conc. HISO#,starch-a C-1, medicine droppers, 0.01 N sodium thiosulfate-aq, stirrer. Procedure: Project C-1 containing 30 ml of orange juice dropperful of starch-aq dropperful of conc. H2S04 (CAREin adding, make sure does not injure the plastic). Now titrate with iodine, (class counting drops), adding about 10 drops in excess. Back-titrate (class counting) with 0.01 N thiosulfate. Wash out cell a t once to prevent iodine stains.



Calculations: Milli-equivalent weight of vitamin C (ascorbic acid) is 0.088. One sample of orange juice had 0.7 mg ascorbic acid per ml of juice. Reference: (1947).




J. Chem. Educ., 24, 458