1) What does positive test mean?

A positive test result indicates the present of whatever nutrient is being tested for.

2) What is the purpose of having a control?

A control, such as distilled water, provides a basis to compare all results. Distilled water, which has been treated to remove all mineral and proteins, should yield negative results on all tests. Therefore if distilled water does not yield negative on a test, it will provide evidence of some form of contamination or flaw with the experiment.

3) Why should the graduated cylinders, test tubes and other glassware be cleaned and rinsed before measuring and testing your solutions?

To prevent contamination of the test equipment from previous experiments which could potentially yield falsified results.

4) Why might a substance taste sweet, yet give a negative reaction with the Benedict’s sugar test?

This draws the conclusion that it is an artificial sweetener. It contains non-reducing chemical structures such as: Aspartame, Saccharin, Neotame, and Surcalose. These chemicals will not hydrolyze unless placed under high temperature or pH and would not provide positive results.

5) You have tested an unknown sample with Biuret and Benedict’s reagents. The solution mixed with biuret reagent is blue. The solution boiled with Benedict’s reagent is also blue. What does this tell you about the sample?

It provides evidence of it lacking either monosaccharide monomers or peptide bonds between them. This could mostly likely be identified as a non-reducing such as sucrose.

6) Several artificial sweeteners are to be tested. Which reagents would you use on a solution of each sweetener? Why? (Hint: you many have to do some researching)

For the testing of the Splenda solution, the most viable option would be the Starch test. This is because it contains Maltodextins, a polysaccharide used in many food additives. It is produced from starch, often found in a hygoscopic powder form.

7) A student heats a test tube containing a large amount of protein and biuret reagent. She notices the colour changes from violet to blue. Explain why heating causes a colour change.

This is because of the chemical reaction at the high temperature; the reagent binds to the protein and the excess heat could cause the protein to denature, reverting it back to its blue colouration temporarily or if it coagulates, permanently.

author avatar
William Anderson (Schoolworkhelper Editorial Team)
William completed his Bachelor of Science and Master of Arts in 2013. He current serves as a lecturer, tutor and freelance writer. In his spare time, he enjoys reading, walking his dog and parasailing. Article last reviewed: 2022 | St. Rosemary Institution © 2010-2024 | Creative Commons 4.0


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