1. do you agree with his conclusion? explain 2. what would be an appropriate con

Question

1. do you agree with his conclusion? explain

2. what would be an appropriate control for this experiment? How would you revise the set - up?

Student A did the experiment using a chemical indicator called Benedict's solution, which turns bright orange when heated in the presence of simple sugars. He had previously verified that the indicator solution was effective by testing it on a known simple sugar, glucose. carried out an experiment to test for the presence of simple sugar in a potato. He To carry out his potato experiment, he added the following to his experimental test tube: ground up potato distilled water 10 drops of glucose solution 5 ml of Benedict's solution Following a few minutes of heating, the Benedict's solution turned bright orange. The student concluded that potato contains simple sugars.

Explanation / Answer

Ans. #1. No. Since glucose (a simple sugar) has been added from outside (not originally derived from the potato sample), it might be responsible for the appearance of bright orange color. The appearance of orange color may or may not have been resulted due to potato sample because the Benedict’s test does not differentiate simple sugars from two different sources – potato sample, and external glucose.

#2. You want to detect the specific color change caused due presence of glucose (simple sugar) in the potato sample, there must be a reference with which the color is compared.

For that, the experiment can be set up as follow- -

I. Positive control:

    Benedicts’ reagent (light blue) + glucose (Colorless) ------> C ( brick red color)

It provides the reference for “positive reaction”. If an unknown sample gives brick red color with Benedicts reagent, it means it also contains glucose.

    Benedicts’ reagent (light blue) + Unknown (Colorless) ------> C (brick red color)

# If the color of the unknown solution after reaction matches that of the control, the unknown solution contains glucose.

II. Negative control:

Benedicts’ reagent (light blue) + Water (Colorless) --------> light blue color

Benedicts’ reagent (light blue) + Unknown (Colorless) ----> light blue color

It provides the reference for “negative reaction”. That is, the color of the solution in absence of reaction with glucose. A test/unknown solution causing no color change or retaining blue color means that glucose is absent in the unknown.

#III. The Test: Incubate ground up potato with 10 drops of distilled water and 5 mL of Benedict’s reagent. Allow the reaction to complete till incubation period.

#IV. Observation: Check the color development in the “Test sample” after incubation period. Compare the color with the positive and negative controls. Under normal condition, the ground potato sample does not contain simple glucose. So, you would see the light blue color, but not orange (or, brick red) color.

#V. Result: The ground potato sample does not contain simple sugar.   

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