CHEM 1030L – Fundamentals of Chemistry Laboratory
An Experimental Design and Investigation
Switchgrass Labs: From Biomass to Biofuel
Note: Be sure to review the Experimental Design Overview presented in Week 1 to
remember what will happen during lab each week during this 3-week experiment.
Overview for Week 2 – Treatment with Enzyme Complex
Week 2 is an intermediate step in the process of converting switchgrass to glucose. In order to
determine if glucose had been produced during the week that the switchgrass samples had undergone
chemical pretreatment, each sample solution will be tested with a glucose test strip. Because enzymes
can function only at very specific pHs, the pH of each experimental mixture will be adjusted before the
enzyme complex is added. After the addition of the enzyme complex to each test tube, each one will be
capped and set aside for one week to allow the enzyme complex to slowly convert the cellulose, which
was freed by the chemical pretreatment in Week 1, to glucose.
Desired Outcome by Week 3: Enzyme complex added to each experimental mixture will break cellulose
down into glucose molecules.
Procedure for Week 2 – Addition of Enzyme Complex
1. Recover the eight test tubes from the first lab.
2. Record appearance, including color, of each experimental mixture on the datasheet. Record any
observed differences from Week 1.
3. Measure pH: Using pH paper, determine the relative pH for each test tube. A simple method is to use a
clean stirring rod. Dip the stirring rod in the test tube and then place a drop of the solution onto the pH
paper. Rinse the stirring rod with distilled water after use in each test tube to avoid contamination.
Compare the moistened pH paper to the color scale on the pH paper container to determine the pH for the
solutions in each test tube. Record the pH for each test tube on the datasheet.
4. Record glucose concentration: Carefully read the package directions for the glucose test strips.
Practice using the glucose test strips by dipping one into the standard glucose solution. Allow the
moistened glucose test strip to rest for the amount of time specified on the package and then read the
results by comparing the color of the test strip to the color chart on the package. The reading should
match the concentration listed on the glucose solution container. Now use a new glucose test strip for
each test tube to measure the glucose concentration of each experimental mixture. Record the glucose
concentrations on the datasheet.
5. Adjust pH to 5.5: Because the cellulase enzyme complex works best at a pH of about 5.5, the contents
of each test tube must be adjusted to a pH of 5.5 before adding the enzyme complex. To do this, any acid
or base added during Week 1 must be neutralized and then a pH 5.5 buffer will be added to each test tube
to maintain that pH.
a. In the test tubes with HCl, add 4 drops of 0.5 M KOH. Mix the contents of the test tube. Use a
stirring rod and pH paper to test the pH of each test tube. If the pH is < 5, add 1 drop of 0.5 M
KOH. If the pH is > 6, add in one drop of 0.5 M HCl. Repeat as necessary to adjust the pH to be
5-6. Record the number of drops of each reagent added on the datasheet. When the pH is in the
proper range, add enough drops of distilled water to bring the total to 20 drops added.
b. To the test tubes with H2SO4, add 8 drops of 0.5 M KOH. Repeat the steps described in step 5a to
mix the contents of the test tube, adjust the pH, and record the number of drops of each reagent
added on the datasheet.
c. To the test tubes treated with KOH add 4 drops of 0.5 M HCl. Repeat the steps described in step
5a to mix the contents of the test tube, adjust the pH, and record the number of drops of each
reagent added on the datasheet.
d. To the test tubes that only had water, add 20 drops of distilled water and record the number of
drops added on the datasheet.
e. Use a small graduated cylinder to acquire approximately 30 mL of the prepared 5.5 pH buffer
solution. Use the calibration line on a disposable pipette to add 1 mL of buffer to each test tube.
f. According to the instructor's directions, each team will prepare one of the following additional
test tubes.
i. Test tube # B – Blank – Use a pipette to add 3 mL of buffer to a clean, dry test tube
ii. Test tube # C – Positive Control: Cotton – Add 0.100 g cotton (a small pinch) to a clean,
dry test tube. Record the exact mass in the data table. Use a stirring rod to push the
cotton to the bottom of the test tube. Use a pipette to add 3 mL of pH 5.5 buffer to the test
tube.
iii. Test tube # MC – Positive Control: Methycellulose – Obtain a tablet of Citrucel (primary
component is methylcellulose). Crush the tablet in a mortar and pestle. Transfer 0.100 g
to a clean, dry test tube. Record the exact mass in the data table. Use a pipette to add 3
mL of pH 5.5 buffer to the test tube.
g. Record final pH: Measure the pH of each solution using a stirring rod and the method described
in Step 3, above, and enter the results on the datasheet. Consult with the instructor if the pH is
not approximately equal to 5.5.
6. When all test tubes have been buffered to 5.0-5.5, take the test tubes to the instructor who will add 500
μL (0.50 mL) of cellulase enzyme complex to the test tubes.
7. Cap and agitate each test tube gently to mix. Store the test tubes at the indicated place to allow the
enzyme complex to work for 7 days (1 week).