Iodine test

A good technical grade of carbon tetrachloride contains not more than the following amounts of impurities 1 ppm acidity as HCl, 1 ppm carbon disulfide if manufactured by carbon disulfide chlorination, 20 ppm bromine, 200 ppm water, and 150 ppm chloroform. The residue should not exceed 10 ppm on total evaporation. The product should give no acid reaction with bromophenol blue, and the starch iodine test should indicate the absence of free chlorine. 

Standard pressure, 54 Standard state, 210 Standard temperature, 54 Starch, 425 iodine test, 358 structure, 431 Stars, 447... 

Since neither the UV nor the iodine test is permanent, it helps to have a record of what you ve seen. You must draw an accurate picture of the plate in your notebook. Using a sharp-pointed object (pen point, capillary tube, etc.) you can trace the outline of the spots on the plate while they are under the UV light (Caution Wear gloves ) or before the iodine fades from the plate. 

Implementation The GC-MS of the sample headspace finds no perfume compounds. The cream is found to be greater than 80-wt% organic matter. Pyrolysis-GC-MS identified significant levels of glucose polymers, which were confirmed by FTIR to be either cellulose or starch. The iodine test revealed that the glucose polymer was starch. Further GC-MS analysis did not find cholesterol, but did find trace levels of a cholesterol degradation product. 

Tetrahydrofuran freshly distilled from lithium aluminum hydride should be used. A commercial product with a peroxide content giving a positive iodine test must be treated with about 0.3% of cuprous chloride (boiling for 30 minutes and distillation) before the addition of the hydride. 

Note The color obtained should be recorded, as it is a definite clue to the compn of the dextrin sample. The iodine test can indicate the extent of hydrolysis dextrin has gone through, and the soly characteristics of the dextrin... 

PLACE LEAF IN IODINE TEST SOLUTION. PARTS EXPOSED TO SUN TURN BLUE. THIS PROVES PRESENCE OF STARCH. UNEXPOSED PARTS BECOME BROWN. 

LINE UP FIVE TEST TUBES, EACH CONTAINING 5 ml WATER AND 1 DROP IODINE TEST SOLUTION. IN ANOTHER TEST TUBE, ADD 2 DROPS OF SALIVA (SPITTLE) TO 5 ml STARCH SOLUTION. PLACE THIS IN GLASS OF WARM (NOT HOT) WATER. WITH 2-MINUTE INTERVALS. DROP 3 DROPS SALIVA-STARCH MIXTURE INTO A TEST TUBE WITH IODINE SOLUTION. SHAKE. COLOR GETS LESS AND LESS BLUE. SALIVA DIGESTS THE STARCH AND TURNS IT INTO A SUGAR. MALTOSE. 

On the basis of the Hanus iodine test performed, what can you say about the nature of the filler in your aspirin tablet ... 

Starch can form an intense, brilliant, dark blue-, or violet-colored complex with iodine. The straight chain component of starch, the amylose, gives a blue color while the branched component, the amylopectin, yields a purple color. In the presence of iodine, the amylose forms helixes inside of which the iodine molecules assemble as long polyiodide chains. The helix-forming branches of amylopectin are much shorter than those of amylose. Therefore, the polyiodide chains are also much shorter in the amylopectin-iodine complex than in the amylose-iodine complex. The result is a different color (purple). When starch is hydrolyzed and broken down to small carbohydrate units, the iodine will not give a dark blue (or purple) color. The iodine test is used in this experiment to indicate the completion of the hydrolysis. 

Sample Condition of hydrolysis Iodine test (positive or negative)... 

The hydrolysis of starch was stopped when the iodine test no longer gave a blue color. Does this mean that the starch solution was completely hydrolyzed to glucose Explain. 

Starch exists in two major forms, amylose and amylopecttn. Although amylose is a linear polymer like cellulose, the a stereochemistry enables the chains to twist and to assume a helical shape. Small molecules such as l2 fit inside the helix and form a complex. This is the basis for the deep blue color in the starch-iodine test. This non-straight or bent conformation is sug-... 

Colour Tests. Iodine Test (omitting Mn02)—positive Lieber-mann s Test—brown-yellow Sulphuric Acid—yellow. 

Colour Tests. Iodine Test—positive Mandelin s Test—red-brown. 

Other nondestructive detection methods use iodine vapors or iodine-potassium iodide reagents (Mylius s reaction). Yellow, orange, or brown zones will appear on the layer. The zones will have to be marked, because the iodine will eventually evaporate. The sensitivity of the iodine test can be greatly increased by the use of layers containing rhodamine 6G. Most of the steroids are recovered unchanged af-... 

Fig. 17-—Iodine test for Schardinger dextrins. Microscopic appearance typical of the early stage of the decomposition of starch by B. macerans amylase. Under higher power the crystals are seen to be blue hexagons.

Fig. 23.—Radioautograph of paper chromatogram separation of mixture obtained by treating radioactive n-gliicose and inactive dextriii with R. marcrans amylase. Gi, Ga, Os, etc., represent n-glucose, maltose, maltotriose, etc. a, 0, y represent the positions to wliicdi the Sehardinger dextrins move. Note that the Schardinger dextrins them.selves do not become radioactive. After the chromatogram was sectioned, inactive a-dextrin was isolated from the band between G4 and Gs and identified by means of the iodine test.

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