5.3: Lab Report
Exercise A: Testing for Carbohydrates
Part 1: Benedict’s Test for Reducing Sugars
Record your results below:
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Data Table for Carbohydrates |
Benedict’s Test (reducing sugars) |
Lugol’s Test (starch) |
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Color before boiling |
Color after boiling |
Color before adding I 2 KI |
Color after adding I 2 KI |
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1) Distilled Water |
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2) Starch |
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3) Glucose |
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4) Maltose |
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5) Sucrose |
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6) Onion juice |
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7) Potato slice |
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8) Milk |
- Examine the carbohydrates data table. Create a hypothesis and a prediction for at least one of the samples you will be testing using Benedict’s test:
Hypothesis: ___________________________________________________________________
Prediction: ____________________________________________________________________
What is the independent variable? ________________________________________________
What is the dependent variable? __________________________________________________
Procedure
- Which samples tested positive for reducing sugars? ____________________________________
- Why did we test water with Benedict’s reagent? _______________________________________
- Did the results from your test support your hypothesis? Yes / No Explain: _________________ ______________________________________________________________________________
Part 2: Lugol’s Test for Starch
- Examine the previous data table. Create a hypothesis and a prediction for at least one of the samples you will be testing using Lugol’s test:
Hypothesis: ___________________________________________________________________
Prediction: ____________________________________________________________________
What is the independent variable? ________________________________________________
What is the dependent variable? __________________________________________________
- Which samples tested positive for starch? ____________________________________
- From the results of your tests, do you think that a potato stores its carbohydrates as sugars or as starch? ________________ Explain: ____________________________________________________________________________________________________
- How does an onion store its carbohydrates? ________________ How can you tell? ________________________________________________________________________________
- Did the results from your test support your hypothesis? Yes / No Explain: _______________________________________________________________________________________________
Exercise B: Testing for Lipids
Part 1: Grease Spot Test for Lipids
Describe the difference between the oil and water drop after drying: ___________________________________________________________________________________________________________________________
Data Table for Lipids
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Substance |
Sudan IV Solubility Reaction (note the color and if + or – for lipids) |
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1) Distilled Water |
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2) Vegetable oil |
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3) Onion juice |
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4) Cola (regular) |
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5) Hamburger juice |
Part 2: Sudan IV Test for Lipids
- Examine the data table for lipids. Create a hypothesis and a prediction for at least one of the samples you will be testing using the Sudan IV test:
Hypothesis: ___________________________________________________________________
Prediction: ____________________________________________________________________
What is the independent variable? ________________________________________________
What is the dependent variable? __________________________________________________
Procedure
- Which samples tested positive for lipids? ____________________________________________
- Why do the red droplets float? ____________________________________________________
- Did the results from your test support your hypothesis? Yes / No Explain: _________________ ______________________________________________________________________________
Exercise C: Testing for Proteins and Amino Acids
Part 1: Biuret Reagent Test for Proteins
- Examine the data table for proteins. Create a hypothesis and a prediction for at least one of the samples you will be testing using biuret reagent:
Hypothesis: ___________________________________________________________________
Prediction: ____________________________________________________________________
What is the independent variable? ________________________________________________
What is the dependent variable? __________________________________________________
Data Table for Proteins
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Substance |
Color with Biuret Reagent after 2 Minutes |
Protein Present (+) or Absent (-) |
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1) Distilled water |
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2) Egg albumin |
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3) Potato starch |
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4) Glucose |
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5) Amino acid |
- Which samples tested positive for proteins? __________________________________________
- What does this test tell you about the biochemical composition of starch or glucose? ________ ______________________________________________________________________________
- Did the results from your test support your hypothesis? Yes / No Explain: _______________________________________________________________________________________________
Part 2: Ninhydrin Test for Amino Acids
- Examine the data table for amino acids. Create a hypothesis and a prediction for at least one of the samples you will be testing using the ninhydrin test:
Hypothesis: ___________________________________________________________________
Prediction: ____________________________________________________________________
What is the independent variable? ________________________________________________
What is the dependent variable? __________________________________________________
Procedure
Complete the table, indicating the content of each solution.
Data Table for Amino Acids
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Solution |
Final Color with Ninhydrin |
Type of Molecule in Solution |
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A |
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B |
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C |
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D |
Exercise D: Testing Unknowns (assigned unknowns: # _________ and # __________)
Data Table for Unknowns
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Unknown Tested |
Positive (+) or Negative (-) Results |
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Benedict’s Test |
Lugol’s Test |
Biuret Test |
Ninhydrin Test |
Sudan IV Test |
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1: |
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2: |
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3: |
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4: |
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5: |
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6: |
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7: |
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8: |
- Your instructor will provide you with a list of the possible unknown contents. Once you have completed the data table, match the names of the unknowns to the numbers in your table by writing the name of the unknown next to each respective