The student tests an unknown solution using each of the tests and observes that the solution turns blue-black when he tests for protein. Which of the following conclusions can the student make? A. The solution contains carbohydrates. B. The solution contains lipids. C. No conclusion can be drawn; the student made an error. D. The solution contains starch. E. The solution contains protein.
Carbohydrates
Carbohydrates are the organic compounds that are obtained in foods and living matters in the shape of sugars, cellulose, and starch. The general formula of carbohydrates is Cn(H2O)2. The ratio of H and O present in carbohydrates is identical to water.
Starch
Starch is a polysaccharide carbohydrate that belongs to the category of polysaccharide carbohydrates.
Mutarotation
The rotation of a particular structure of the chiral compound because of the epimerization is called mutarotation. It is the repercussion of the ring chain tautomerism. In terms of glucose, this can be defined as the modification in the equilibrium of the α- and β- glucose anomers upon its dissolution in the solvent water. This process is usually seen in the chemistry of carbohydrates.
L Sugar
A chemical compound that is represented with a molecular formula C6H12O6 is called L-(-) sugar. At the carbon’s 5th position, the hydroxyl group is placed to the compound’s left and therefore the sugar is represented as L(-)-sugar. It is capable of rotating the polarized light’s plane in the direction anticlockwise. L isomers are one of the 2 isomers formed by the configurational stereochemistry of the carbohydrates.
A student is testing for the presence of protein, simple sugars, starch, and lipids using the tests summarized in the table below.
| Molecule | Test | Positive Result | Negative Result |
| Protein | Biuret reagent | Pink or purple | Blue |
| Simple sugars | Benedict's reagent | Green, Orange or Red | Blue |
| Starch | Iodine | Orange, Blue or Purple | Yellow |
| Lipids | Brown paper | Oily Stain | No stain |
The student tests an unknown solution using each of the tests and observes that the solution turns blue-black when he tests for protein. Which of the following conclusions can the student make?
A. The solution contains carbohydrates.
B. The solution contains lipids.
C. No conclusion can be drawn; the student made an error.
D. The solution contains starch.
E. The solution contains protein.
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