QUESTIONS AND PROBLEMS 1. The possible carbohydrates in the following problems a
ID: 1031861 • Letter: Q
Question
QUESTIONS AND PROBLEMS 1. The possible carbohydrates in the following problems are limited to these: arabinose, glu- cose, fructose, maltose, sucrose, and starch. (a) A carbohydrate solution gave a positive Molisch test and negative Benedict, Barfoed, Bial, and Seliwanoff tests. When treated with hydrochloric acid and boiled for sever- al minutes, the solution showed positive Benedict, Barfoed, and Seliwanoff tests and a negative Bial test. Which carbohydrate was in the original solution? (b) A solution containing only one carbohydrate gave a Cu2O precipitate with Benedict reagent. Which of the carbohydrates is present in the solution? (c) Another sample of the solution from (b) failed to give a Cu20 precipitate with Barfoed reagent. Which carbohydrate is present in the solution?Explanation / Answer
Answer:
(a) The carbohydrate present in the original solution is sucrose.
Because it has shown possitive Benedict's, Barfoed's and seliwnaffs test after heating with hydrochloride acid. Before heating it has shown negative test. glucose, fructose, arabinose and maltose are reducing sugars, therefore they show readily all of them possitive tests.
Sucorse is a disaccharide which under goes hydrolysis after heating with HCl solution and converts into fructose and glucose. These are reducing sugars, which shows possitive result for these tests.
(b) The solution contains fructose.
(c) The solution contains Sucrose. (Barfoed's test is for identifying disaccharides and monosaccharides).
though maltose is also a disaccharide but it acts as reducing sugars.