224 DIY Science: Illustrated Guide to Home Chemistry Experiments
CUTIOA nS
Sulfuric acid is corrosive. Hydrogen peroxide is a strong
oxidizer and bleach. Potassium permanganate is a strong
oxidizer and stains skin and clothing. Wear splash goggles,
gloves, and protective clothing at all times.z
SBSTITUTIU oNS ANd modIfICATIoNS- If you don’t have six 150 mL beakers, you may
substitute Erlenmeyer flasks, foam cups, or other
containers of similar capacity. Alternatively, you can
complete this lab session using only one beaker or
other container by doing the timed runs sequentially
instead of simultaneously. - You may substitute a 10 mL graduated cylinder for the
10 mL pipette, at the expense of accuracy. - If you do not have a burette, you may use the
alternative titration procedure described in Chapter 5. - If you do not have a stopwatch, you may substitute a
timer or watch with a second hand. - Rather than purchase catalase enzyme, you may
substitute a dilute solution of animal blood, which
contains catalase. The liquid that leaks from a package
of raw ground beef suffices, or you can obtain a small
amount of animal blood from a butcher. The exact
concentration of catalase in unimportant, as long as
that concentration is the same for all of your test runs.
One or two mL of animal blood diluted with distilled
water to 10 mL works well.
POCEDURER
1.f you have not already done so, put on your splash I
goggles, gloves, and protective clothing.
- Transfer about 40 mL of the sulfuric acid to the 100 mL
graduated cylinder. - Fill the 10 mL graduated cylinder with the catalase solution.
- Label six beakers or other containers from A through F.
- Use the pipette to transfer as closely as possible 10.00
mL of the hydrogen peroxide solution to each of the
beakers. Record the amount of hydrogen peroxide in each
beaker to 0.01 mL on the corresponding line in Table 12-4. - Beaker A is the control, to which we will not add any
catalase enzyme. Set it aside for now. - Use the Beral pipette to withdraw 1.0 mL of catalase
solution from the 10 mL graduated cylinder. - As close to simultaneously as possible, start the
stopwatch or timer and squirt the catalase solution into
beaker B. Swirl the beaker to mix the solutions. - With the graduated cylinder of sulfuric acid held ready,
when the timer reaches the 15.0 second mark, dump the
sulfuric acid quickly into beaker B and swirl to stop the
reaction. Record the elapsed reaction time as closely as
possible on the corresponding line in Table 12-4.
Refill the 100 mL graduated cylinder with 40 mL of
sulfuric acid solution.
Repeat steps 7 through 10 for beakers C, D, E, and F using
reaction times of 30 seconds, 60 seconds, 120 seconds,
and 240 seconds.
Set up your burette, rinse it with the 0.1 M potassium
permanganate titrant, and refill it to near the 0.00 mL line.
Titrate the solution in beaker A by adding titrant to the
beaker until a slight purple coloration just persists.
Record the volume of titrant required to 0.01 mL on the
corresponding line in Table 12-4. (Assuming nominal
concentrations, about 35 mL of titrant should be required
for beaker A, and correspondingly less for beakers B, C,
D, E, and F.)
Repeat step 13 for beakers B, C, D, and E. For each titration,
calculate the number of millimoles (mM) of potassium
permanganate required to neutralize the remaining
hydrogen peroxide. (One millimole is 0.001 mole. Using
mM locates the decimal point more conveniently for
calculations.) Enter the number of millimoles of titrant
required for each titration in Table 12-4.
Using the balanced equation provided in the introduction,
calculate the number of millimoles of unreacted hydrogen
peroxide in each beaker, and enter that value in Table 12-4.
For each beaker, calculate the reaction rate in millimoles/
second (mM/s) and enter that value in Table 12-4.Too ASTf oR Too SLow
If the reaction is so vigorous that the solution foams over
the top of the container, repeat step 8 using a more dilute
catalase solution, and use that more dilute solution for the
following steps as well. If the reaction rate is too slow—not
enough bubbles forming quickly enough—use a more
concentrated catalase solution or more of it.