Starch iodide coloration

Starch Iodide coloration. To a small volume of starch solution ... 

Free nitrous acid causes an immediate blue color at the point of contact with starch-iodide test paper. A delayed color or a color around the periphery of the wetted area is of no significance. At all times there must be an excess of mineral acid (blue color on Congo paper). 

On standing, the filtered solids take on a color characteristic of iodine the solids can be decomposed by treatment in water with sodium thiosulfate or bisulfite to a negative starch-iodide endpoint. 

A positive test is the immediate formation of a dark violet or brown spot on starch-iodide paper moistened with 2N hydrochloric acid. A negative test may consist of a very faint beige color or complete absence of color. 

In a 2-1. beaker, set in a freezing mixture and provided with a stirrer and a thermometer for reading temperatures to o°, are placed 500 cc. of water, 137 g. (1 mole) of anthranilic acid and 200 cc. of concentrated hydrochloric acid the stirrer is started and the mixture cooled to about 6°. Meanwhile 69 g. (1 mole) of sodium nitrite is dissolved in 280 cc. of hot water and the solution cooled in ice portions are then placed in a separatory funnel of convenient size, supported in such a way that the lower end of the stem extends beneath the surface of the anthranilic acid solution. When the temperature has fallen to 50, the nitrite solution is run in, about 500 g. of cracked ice is added at such a rate as to keep the temperature below 50. This takes about ten minutes (Note 1). A drop of the solution should give an immediate blue color with starch-iodide paper. 

A drop of the reaction mixture is placed on a moist piece of starch-iodide paper. The development of a blue color shows the presence of lead tetraacetate. 

A commun means of detecting hypochlorites is the production of u blue color (caused by free iodine) with starch iodide paper by hypochlorites in weakly alkaline solution. Silver nitrate also precipitates part of the hypochlorite in solutions as white silver chloride. 

About 50 grams of the sample are mixed intimately in a flask with 10 c.c. of 25% phosphoric add. The flask is then closed with a cork, between which and the neck of the flask is placed a strip of starch-iodide paper moistened at the lower end, which is adjusted so as to be about 1 cm. from the meat. If the paper exhibits no coloration in the course of a few minutes the flask is heated in a water-bath until it attains the temperature of the... 

The end-point of the titration is measured by the persistence of intermediate I2 in the solution, signalled by the blue color of a starch-iodide complex. 10 mL of 0.2% starch and at least 3 g of NaHCCb are added to 50 mL of the sodium hypochlorite aqueous solution. A titration is performed by dropping a standard 0.02 M potassium iodide solution. The end of the titration is signalled by the persistence of the blue color of the starch-iodide complex. 

Notes. (1) The completion of the reaction may be confirmed by treating starch-iodide paper with a drop of the reaction solution. At the end of the reaction no coloration is observed. 

Wear a face shield and goggles, butyl rubber gloves, and a laboratory coat. Cover the spill with a 1 1 1 mixture by weight of sodium carbonate or calcium carbonate, clay cat litter (bentonite), and sand. Using a plastic scoop, shovel the mixture into a plastic container and transport to the fume hood. Slowly add to a pail of cold water. Avoid contact with metal. To the aqueous solution add an ice-cold concentrated aqueous solution of sodium bisulfite until a drop of the mixture on starch-iodide paper does not produce a blue color. Test the pH of the solution and neutralize with 5% aqueous hydrochloric acid or sodium carbonate as appropriate. Decant the solution to the drain. Treat the solid residue as normal refuse.6,7... 

Wear a face shield, goggles, butyl rubber gloves, and a laboratory coat. In the fume hood behind a shield, slowly add the peracetic acid to a large volume of ice-cold, saturated sodium bisulfite solution. Test a drop of the solution with starch-iodide paper. If a blue color is produced, add more saturated sodium bisulfite solution. Neutralize the solution with 5% aqueous hydrochloric acid or with sodium carbonate as appropriate. Wash into the drain.7... 

To test for peroxides add 0.5 cc. of the isopropyl alcohol to 1 cc. of a 10% potassium iodide solution acidified with 0.5 cc. of dilute (1 5) hydrochloric acid. The test is positive if the yellow color of liberated iodine appears in one minute it is still more sensitive if a few drops of 2% starch solution are added to this iodine solution to give the blue-black starch-iodine color. 

To 50 cc. of water, add 1 cc. of KI solution and 1 cc. of starch emulsion. Note absence of blue color. To half of this starch-iodide solution, add a few crystals of sodium perborate and then a drop or two of acetic acid until a blue color appears. To the other half of the starch-iodide, add a few drops of hydrogen peroxide and note a blue color which disappears when a drop or two of 6 N NaOH is added. Write equations and compare the action of sodium perborate and hydrogen peroxide. 

Analysis of the products showed that ethylene and hydrobromic acid are practically the only gases remaining after the reaction is completed. The flask was opened under a starch iodide solution, but no test for free bromine could be obtained. In none of the work did the brown color of bromine develop even at high tem-... 

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