Your Full Name:
INSTRUCTIONS:
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On your own and without assistance, complete this Lab 2 Answer Sheet
electronically and submit it via the Assignments Folder by the date listed in the
Course Schedule (under Syllabus).
To conduct your laboratory exercises, use the Laboratory Manual located under
Course Content. Read the introduction and the directions for each
exercise/experiment carefully before completing the exercises/experiments and
answering the questions.
Save your Lab 2 Answer Sheet in the following format: LastName_Lab2 (e.g.,
Smith_Lab2).
You should submit your document as a Word (.doc or .docx) or Rich Text Format
(.rtf) file for best compatibility.
Pre-Lab Questions
1. Nitrogen fixation is a natural process by which inert or unreactive forms of
nitrogen are transformed into usable nitrogen. Why is this process important to
life?
2. Given when you have learned about the hydrogen bonding shared between
nucleic acids in DNA, which pair is more stable under increasing heat: adenine
and thymine, or cytosine and guanine? Explain why.
3.
Which of the following is not an organic molecule; Methane (CH4), Fructose
(C6H12O6), Ethanol (C6H12O), or Ammonia (NH3)? How do you know?
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Experiment 1: Testing for Proteins
Materials
(2) 250 mL Beakers
25 Drops Biuret Solution,
H2NC(O)NHC(O)NH
(1) Knox® Gelatin Packet
5 mL 1% Glucose Solution, C6H12O6
(1) 10 mL Graduated Cylinder
(1) 100 mL Graduated Cylinder
Permanent Marker
5 Pipettes
5 Test Tubes (Glass)
Test Tube Rack
5 mL Unknown Solution
*Egg White
*Hot Water
*Tap Water
*You Must Provide
The protein molecules in many foods provide the amino acid building blocks
required by our own cells to produce new proteins. To determine whether a
sample contains protein, a reagent called Biuret solution is used. Biuret
solution contains copper ions, similar to Benedict’s solution (another common
reagent). However, the chemical state of the copper ions in Biuret solution
causes them to form a chemical complex with the peptide bonds between
amino acids (when present), changing the color of the solution. Biuret solution
is normally blue, but changes to pink when short peptides are present and to
violet when long polypeptides are present.
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Figure 6: Biuret solution only is located on the
far left side of the image (blue). Note the
transition from blue to violet as proteins are
added to the solution, causing the solution to
transition from blue to violet.
Procedure
1. Predicted results based on a previously learned set of information is
sometimes called an a priori prediction. Before you begin, take a
moment to construct a priori predictions stating whether or not there
are proteins present in each of the following solutions: Albumin (Egg
White), Knox® Gelatin, Glucose, and Water. Record these predictions in
Table 1.
2. Then, use your knowledge of Biuret solution chemistry (refer to the
experimental introduction) to predict the color of each of the four
solutions when mixed with Biuret solution. You must predict the initial
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color, as well as the final color (the color after ). Record these
predictions in Table 1.
3. You may now begin your experiment by using the permanent marker to
label five test tubes 1, 2, 3, 4 and 5.
4. Prepare your testing samples as follows:
a. Mix one egg white with 25 mL water in a 250 mL beaker to create
an albumin solution. Pipette 5 mL of this solution into Test Tube
1.
b. Mix the packet of Knox® gelatin with 50 mL hot water in a second
250 mL beaker. Stir until dissolved. Pipette 5 mL of this solution
into Test Tube 2.
5. Pipette 5 mL of the 1% glucose solution into Test Tube 3.
6. Use the 10 mL graduated cylinder to measure and pour 5 mL of water
into Test Tube 4.
7. Pipette 5 mL of the “Unknown Solution” into Test Tube 5.
8. Add five drops of Biuret solution to each test tube. Swirl each tube to
mix.
9. Record the initial color of each sample in Table 2.
10. Record the final color in Table 2.
Note: Protein is present in the sample if a light purple color is observed.
Experiment 1: Testing for Proteins
Data Tables and Post-Lab Assessment
Table 1: A Priori Predictions
Table 1: A Priori Predictions
Sample
Will There
be Protein Initial Color
Present?
Final Color
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1 - Albumin Solution
2 - Gelatin Solution
3 - Glucose
4 - Water
5 - Unknown
Table 2: Testing for Proteins Results
Table 2: Testing for Proteins Results
Sample
Initial Color
Initial Color
Is Protein Present?
1 - Albumin Solution
2 - Gelatin Solution
3 - Glucose
4 - Water
5 - Unknown
Post-Lab Questions
1. How did your a priori predictions from Table 1 compare to your actual results in
Table 2? If there were any inconsistencies, explain why this occurred.
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2. Identify the positive and negative controls used in this experiment. Explain how each
of these controls are used, and why they are necessary to validate the experimental
results.
3. Identify two regions which proteins are vital components in the human body. Why are
they important to these regions?
4. Diet and nutrition are closely linked to the study of biomolecules. Describe one
method by which you could monitor your food intake to ensure the cells in your body
have the materials necessary to function.
Experiment 2: Testing for Reducing Sugars
Many of the foods we eat contain carbohydrates. Monosaccharides and short
chains such as disaccharides taste sweet due to certain aspects of their
chemical structure. A structural characteristic of some sugars can be identified
using a chemical solution called Benedict’s reagent. When heated, the copper
ions in Benedict’s solution react with the free end of any reducing sugars, such
as glucose molecules. Copper ions are reduced by the sugars, producing an
orange or red colored precipitate.
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Materials
5 mL Benedict’s Solution
5 mL 1% Glucose Solution, C6H12O6
10 mL Graduated Cylinder
Permanent Marker
3 Pipettes
Ruler
Spatula
5 Test Tubes (Glass)
Thermometer
5 mL Unknown Solution
*Fork
*Hot Water Bath (stovetop or microwave and
a deep, heat-safe bowl)
*Knife
*Onion
*Potato
*Stopwatch
*Tap Water
*You Must Provide
Note: Use great caution when handling a knife and/or cutting. Ask for
assistance if you need help or are uncomfortable with knife work.
Procedure
1. Label five test tubes as 1 - 5.
2. Prepare your testing samples as follows:
a. Cut a raw potato into a 1.0 cm x 1.0 cm x 1 cm cube. Cut this
cube into smaller pieces, and mash with a fork and
approximately 5 - 10 drops of water. Place half of the mashed
raw potato into Test Tube 1. Use the 10 mL graduated cylinder to
measure and pour 5 mL of water into Test Tube 1.
b. Cut a raw onion into a 1.0 cm x 1.0 cm x 1.0 cm cube. Cut this
cube into smaller pieces, and finally mash with a clean or new
fork. Place half of the mashed raw onion into Test Tube 2. Use
the 10 mL graduated cylinder to measure and pour 5 mL of water
into Test Tube 2.
3. Pipette 5 mL of the 1% glucose solution into Test Tube 3.
4. Use the 10 mL graduated cylinder to measure and pour 5 mL of water
into Test Tube 4.
5. Pipette 5 mL of the “Unknown” solution into Test Tube 5.
6. Record the initial color of each solution in Table 3.
7. Prepare a hot water bath using the following information:
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a. Heat water to a temperature between 85 and 100 °C (not boiling)
using a stovetop or microwave safe container. Be sure to confirm
this temperature using the thermometer just prior to use in Step
9. The hot water bath must be of appropriate size and shape to
fit five glass test tubes in a vertical orientation.
8. Pipette 10 drops of Benedict’s Solution to each test tube. Swirl each
tube gently to mix.
9. Place the five test tubes into the hot water bath and let sit for three
minutes. Remove the tubes from water and place them in test tube rack
to cool for five minutes.
10. Record the final color in Table 3.
Note: A reducing sugar is present in the sample if a red, yellow or green
precipitant forms. Wash your test tubes immediately after recording
results to prevent permanent staining from the reaction products
Experiment 2: Testing for Reducing Sugars
Data Tables and Post-Lab Assessment
Table 3: Testing for Reducing Sugars Results
Table 3: Testing for Reducing Sugars Results
Sample
Initial Color
Final Color
Reducing Sugar
Present
1 - Potato
2 - Onion
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3 - Glucose Solution
4 - Water
5 - Unknown
Post-Lab Questions
1. Write a statement to explain the molecular composition of the unknown solution
based on the results obtained during testing with each reagent.
2. What can you conclude about the molecular make-up of potatoes and onions
based on the test you performed? Why might these foods contain these
substance(s)?
3. What results would you expect if you tested ribose, a monosaccharide, with
Benedict’s solution? Biuret solution?
Experiment 3: What Household Substances are Acidic or
Basic?
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In the following experiment, you will be using pH test strips to determine the
pH of various household substances. pH stands for “potential hydrogen” and is
broken into a scale of 1 - 14 to indicate the acidity or basicity of a solution.
Generally speaking, more hydrogen ions in a solution correlates to lower pH
values, and more acidic solutions. Conversely, fewer hydrogen ions correlates
to higher pH values, and more basic solutions. 7 is located in the middle of this
number scale, and represents neutral solutions.
Figure 7: Note that many strong acids and bases do not have a pH that is indicated on
this scale. For example, lead battery acid has a pH that is below one.
Refer to the color key provided in the module with your pH test strips to
determine which color corresponds to each pH value. In this way, pH paper
allows scientists to determine to what degree a substance is acidic or basic
and can provide an approximate pH value.
Materials
5 mL 4.5% Acetic Acid (Vinegar), C2H4O2
(3) 100 mL Beakers
(3) 250 mL Beakers
10 mL Graduated Cylinder
(10) pH Test Strips
5 mL Sodium Bicarbonate (Baking
Soda)Solution, NaHC)3
*4 Liquid, Household Solutions
*Paper Towels
*Water Source (Jug or Sink)
*You Must Provide
Procedure
1. Find four household substances to test (ex: grape juice, lemon juice,
dishwashing liquid, milk, tomato juice, shampoo, corn starch solution,
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2.
3.
4.
5.
6.
etc.). You will use the vinegar (acidic) and sodium bicarbonate (basic)
solution provided in your kit as standards.
Predict the pH of each substance before testing with a pH strip. Record
your predictions in Table 4.
Use the permanent marker to label each of the beakers with the name
of one of the six solutions. It does not matter which size beaker is used
for the different solutions.
Use the graduated cylinder to measure and pour five mL of vinegar into
the beaker labeled “Vinegar”.
Thoroughly rinse the graduated cylinder with water to remove any
remaining vinegar. Use paper towels to dry the graduated cylinder and
repeat Step 4 with each of the five remaining solutions and beakers.
Measure the pH of each solution by dipping the pad of the pH strip into
the solution for 5 - 10 seconds and comparing it with the pH test strip
key (located in the lab module). Record your results in Table 4.
Experiment 3: What Household Substances are Acidic or
Basic?
Data Tables and Post-Lab Assessment
Table 4: pH Values of Common Household Substances
Table 4: pH Values of Common Household Substances
Substance
pH Prediction
pH Test Strip Color
Acetic Acid (Vinegar)
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Sodium Bicarbonate Solution (Baking Soda)
Post-Lab Questions
1. What is the purpose of determining the pH of the acetic acid and the sodium
bicarbonate solution before testing the other household substances?
2. Compare and contrast acids and bases in terms of their H+ ion and OH- ion
concentrations.
3. Name two acids and two bases you often use.
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