Please Explain the pre-lab questions The reaction by which the red tetrazolium t
ID: 54029 • Letter: P
Question
Please Explain the pre-lab questions
The reaction by which the red tetrazolium test gives a positive result. The product is insoluble and red in color. A table of this nature should be in your lab notebook. Make the squares large enough to record visual observations. Which reagent would be best for converting D-fructose to D-mannitol? What determines whether or not a sugar is reducing? Draw a mechanism for the reaction in Figure 2. Before coming to lab; fill out Table 1 with expected results. Draw a '+' where you expect a positive test result and a where you expect a negative or no result. If you don't fill this out correctly before lab, you won't be able to do the lab and will be given a zero.Explanation / Answer
1. NaBH4 reduces D-fructose to a mixture of alditols (aldo alcohols) D-glucitol and D-mannitol at 1:1 ratio.
2. A sugar will be a reducing sugar if it has an open chain conformation, with a free aldehyde/keto group or a free hemiaetal/hemiketal group.
4.
Molisch’s test
Red – tetrazolium
Barfoed’s
Bial’s test
Seliwanov’s Test
D-Fructose
+
+
+
+
+
D-glucose
+
+
+
+
+
Lactose
+
+
+
-
-
D-Mannitol
+
+
+
-
-
Sucrose
+
-
-
-
-
D-Xylose
+
+
+
+
+
Molisch’s test
Red – tetrazolium
Barfoed’s
Bial’s test
Seliwanov’s Test
D-Fructose
+
+
+
+
+
D-glucose
+
+
+
+
+
Lactose
+
+
+
-
-
D-Mannitol
+
+
+
-
-
Sucrose
+
-
-
-
-
D-Xylose
+
+
+
+
+