Olivia wants to test an unknown liquid to see if it contains protein. She sets u

Question

Olivia wants to test an unknown liquid to see if it contains protein. She sets up 3 test tubes each with 10mL of the following: distilled water, gelatin solution and the unknown. The water is clear, the gelatin solution is clear with a yellow tint, and the unknown is cloudy white. She uses Biuret's Reagent - which is a dark blue dye, which will turn a liquid sample purple in the presence of protein.

1. Predict what color the water will change when Biuret's Reagent is added:____________ (clear white, clear blue, or clear purple)

2. Predict what color the gelatin solution will turn when Biuret's Reagent is added:____________ (clear white, clear blue, or clear purple)

3. Olivia has both a positive and negative control for this experiment. The water is the __________ control, whereas the gelatin in the _________ control.

4. If protein is present in the unknown, what color should the unknown turn?  ___________ (cloudy white , cloudy blue , cloudy purple)

5. If Olivia tested a 1% sucrose solution (which is normally clear), what color would you predict it to be after adding Biuret's Reagent? _________ (clear white, clear blue, clear purple)

Explanation / Answer

Hi
The Biuret's solution is specific to proteins and turns to purple in th presence of it. So if the colour of the solution turns to purple, it means the solution has proteins;If the colur of the sample after addition of Biurett's solution remains as dark blue/cloudy blue, then there is no protein in the sample.

1. When the reagent is added to the water, the color of water turns to clear blue. No proteins.
2. The color of gelatin will turn to Clear purple, when reagent is added. Gelatin is made of collage, which is a protein.
3. The water isa negative control: A control where we get negative results, or the control where the expected reactions do not take place,is called Negative control. It helps to remove any background interference. The gelatin is a positive control; A control where expected reactions do occur and we get expected results is called Positive control. Such controls help us to know whether the experiment worked.
4. If the protein is present in the unknown, it should turn to cloudy purple.
5. If the 1% sucrose solution is tested with Biurett reagent, the color of the solution will be clear blue; The sucrose is no protein and hence will not react with Biurett.

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