Lab2:The Chemistry of Life Pre-Lab Questions Nitrogen fixation is a natural process by which inert o

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Lab2:The Chemistry of Life
Pre-Lab Questions
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?
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.
Which of the following is not an organic
molecule; Methane (CH4), Fructose (C6H12O6),
Ethanol (C6H12O), or Ammonia (NH3)? How
do you know?

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

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.

.jpg” alt=”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. “>

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
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.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
color, as well as the final color (the color after ). Record these
predictions in Table 1.You may now begin your experiment by using the permanent marker to
label five test tubes 1, 2, 3, 4 and 5.Prepare your testing samples as follows: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.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.Pipette 5 mL of the 1% glucose solution into Test Tube 3.Use the 10 mL graduated cylinder to measure and pour 5 mL of water
into Test Tube 4.Pipette 5 mL of the “Unknown Solution” into Test Tube 5.Add five drops of Biuret solution to each test tube. Swirl each tube
to mix.Record the initial color of each sample in Table 2.Record the final color in Table 2.
Note: Protein is present in the sample if a light purple color is
observed.
Data
Tables and Post-Lab Assessment
Table 1: A Priori Predictions

Table 1: A Priori
Predictions

Sample

Will There be Protein
Present?

Initial Color

Final Color

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.
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.

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

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.

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
Label five test tubes as 1 – 5.Prepare your testing samples as follows: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.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.Pipette 5 mL of the 1% glucose solution into Test
Tube 3.Use the 10 mL graduated cylinder to measure and
pour 5 mL of water into Test Tube 4.Pipette 5 mL of the “Unknown” solution into Test
Tube 5.Record the initial color of each solution in Table
3.Prepare a hot water bath using the following
information: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.Pipette 10 drops of Benedict’s Solution to each
test tube. Swirl each tube gently to mix.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.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.

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

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?
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.

.jpg” alt=”Figure 1: “>

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)

Procedure
Find four household substances to test (ex: grape juice, lemon juice,
dishwashing liquid, milk, tomato juice, shampoo, corn starch solution,
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.

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)

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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