Laboratory Manual for General, Organic, and Biochemistry, Seventh dtion 143 367
ID: 304142 • Letter: L
Question
Laboratory Manual for General, Organic, and Biochemistry, Seventh dtion 143 367 Locker Number Date_ Experiment 26 The Characterlzation of Carbohydrates Name Please print lest name fst REPORT SHEET: A. Characterizing Known Carbohydrates 1. The Molisch Test Record the color produced by each carbohydrate and the time required for a positive test: 1-xylose- nbos 3. fructose0 5. starch 2. glucose 6. control 4. sucrose Which carbohydrates gave a positive test? Did any carbohydrate(s) require an extended time to give a positive test? 2. Iodine Test Record the color produced by each carbohydrate: 1-xylose bos 2. glucose 4. starch . amylopectin 5. glycogon 8. cellulose 6. amylose 9. control 3. sucrose Which carbohydrate(s) gave a positive iodine test? Which of these are polysaccharides?Explanation / Answer
Molischs test is a general test for all carbohydrates ( monosachrides , disachrides ,polysachrides etc).In this test , The cabohydrate is treated with concentrated H2SO4 for dehydration into an aldehyde and then condensed with two phenols ( Resourcinol and alpha naphthol). Positive result is the formation of violet ring around the acid interface. The time taking for the reaction is asked to make your inference during the experiment. generally monosachrides gives fast result .Monosacchrides and polysachrides like starch takes a little more time to produce violet ring.
a)All the carbohydrates gives positive test for Molishes test except for the control ( for control we will add all the reagents except for the substance to be analysed, it is to make sure that the reagent does not produce any violet colour without the presence of carbohydrates)
b)The disachrides like sucrose and polysachrides develops violet colour slower.
Iodine Test
Iodine test is a particular test used to identify the presence of starch. In this test iodine solution dissolve in aqueos solution of KI is added to the substance to be analysed , This iodine solution has a light orange brown colour.If the starch is present the colour of the solution turns blue black.
a)starch, amylose ,amylopectin gives blue black colour which is positive for iodine test. among the polysachride glycogen gives a blue brown colour with iodine solution rest all polysachrides gives negative iodine test.
b) Among these starch, amylose ,amylopectin,glycogen, cellulose are polysachrides.
Benedicts test
Benedict test is to detect the presence of reducing sugars.Reducing sugar has free aldehyde or ketonic group. When the the subatance is treated with benedicts solution. The reducing sugar is oxidised by the copper ion in the solution to form carboxylic acid and a red precipite of copper I oxide is formed. This is the principle of benedicts test. The concentration of sugar affects the colour of test from green to brick red.
Xylose - positive result for benedicts test
fructose - positive result for benedicts test
Lactose - positive result for benedicts test
Maltose - positive result for benedicts test
glucose - positive result for benedicts test
Sucrose - negative result for benedicts test
Starch - negative result for benedicts test
Galactose -positive result for benedicts test
a) Xylose ,fructose,lactose,glucose,galactose,maltose are reducing sugars
b) Xylose, fructose ,galactose,glucose are reducing monosachrides
c) lactose and maltose are reducing disachrides
d) sucrose is a non reducing disachride and starch is a non reducing polysachride.
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