This is similar to the exercise that I use in CHM 1102, Organic and Biochemistry (q.v.). Students run classic qualitative assays for reducing sugars, ketoses, and pentoses,  then use those assays to characterize sugars produced by hydrolysis of corn starch, sawdust, dandelion root, and gum arabic.

For the exercise, students are provided with 1% (w/v) solutions of D-glucose, D-fructose, L-arabinose, lactose, maltose, sucrose, D-xylose, and D-sorbitol on which they will carry out Benedict's, Seliwanoff's, and Bial's tests. They also have prepared (the previous week) acid hydrolysates of the polysaccharides listed above. Hydrolysates are prepared by heating 0.25 g of polysaccharide source with 5 mL of 1 M HCl in an 80 degree oven for two days. Each extract is neutralized with 1 mL of 20% (w/v) NaOH; extracts of corn starch and gum arabic are diluted with an equal volume of water. The samples are then filtered into labeled containers for the qualitative tests.

For write-up, students are to draw the structures of the eight carbohydrates to be used and identify each as monosaccharide/disaccharide; reducing/nonreducing; pentose/hexose; aldose, ketose; or sugar alcohol. After tabulating all their observations, they are asked to prepare descriptions of positive tests as well as color changes that should be considered negative results. They are then asked to characterize, as well as the tests allow, sugars produced in the acid hydrolyses.

Revised 6/11/07