Organic 2 Review Problem 383

Organic 2 Review Problem 383 - R EACTIONS A ND I...

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REACTIONS AND IDENTIFICATION 367 water. So-called "starch solution" or "starch paste" is prepared as follows: Place about i g. of starch in a test-tube, add about io ml. of water, and mix well. Pour this suspension with stirring into ioo ml. of boiling water and continue to boil the mixture for i minute. A soluble starch is obtainable which dissolves slightly in cold water and readily in hot water to give a clear solution. Concentrated solutions of both "soluble starch" and "ordinary starch" set to a jelly on cooling. GENERAL REACTIONS. 1. Respond to Molisch's Test. 2. Blackening and effervescence when warmed with cone. H 2 SO 4 . 3. Certain carbohydrates give yellow colorations when boiled with NaOH solution. 1. Molisch's Test. Dissolve about o-i g. of the carbohydrate in z ml. of water (for starch use 2 ml. of "starch solution"), add 2-3 drops of a i % alcoholic solution of i-naphthol (ignoring traces of the latter precipitated by the water) and then carefully pour 2 ml. of cone. H
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