Please report each answer to the correct number of significant figures. Please l

Question

Please report each answer to the correct number of significant figures. Please label each answer and write clearly (so I can read). Thank you!!!!

Please report each answer to the correct number of significant figures. Please label each answer and write clearly (so I can read). Thank you!!!!

Experiment 12 Prelaboratory Assignment Carbohydrates Name: Date Lab instructor: a e3 Record each answer in the space provided. 1. The following observations were recorded for an unknown carbohy- drate. What is the identity of the unknown carbohydrate (fructose glucose, maltose, starch, sucrose, xylose)? Test Color Iodine Test no color Barfoed red Bial brown Seliwanoff peach 2. You will perform five qualitative assays (tests which will be used unknown carbohydrate How many of those assays to identi require boiling water? 3. Is the Cu2+ on oxidized or reduced in Benedict's test? 4. Label Figure 12 h the expected change for each reaction. You wil s in your lab manual to aid in your experi t, but you should show structor for credit. 163

Explanation / Answer

These tests are qualitative. So there is no scope of having any digits. Hence the significant figures are not applicble.

1. Let's look at all the test one by one

Iodine test - Iodine solution gives Red to black color only with starch. Since the result here is colorless, so this carbohydrate is not starch.

Barfoed test - It is to detect monosaccharides. The red color is dueto formation of copper(I) oxide (Cu2O). So, this carbohydrate is not maltose or sucrose (both are disaccharides)

Bial test - This is to identify Pentoses. Only pentoses give blue color. All other colors are negative for pentoses. Also, hexoses may give brown redor green products. So, in this case, xylose is ruled out (pentose).

Seliwanoff's test - This is to distinguish aldose & ketose. Since the color is peach (light pink), it is glucose as it is aldose. Fructose will give a very deep red color.

So, from the above tests, the carbohaydrate is identified to be Glucose.

3. Benedict's solution contains Cupric Sulfate (CuSO4). So, it is blue in color. It is an alkaline solution used to identify reducing sugars having (-CHO) group. If reducing sugar is present, a deep red precipitate is formed. This is due to formation of copper(I) oxide (Cu2O).

So, the initial Cu2+ is reduced to Cu+.

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