Lab Report 3: Buffer Systems 1
Lab Report 3: Evaluating the Effectiveness of Buffer Systems
Manager Recorder Lab Tech Computer Tech
On campus students: Attach your Logger Pro graph to this Lab Report.
Online students: Use graph and data attached to this assignment folder in D2L. 1. State your hypothesis.
2a. In this experiment, what was the independent variable?
2b. What was the dependent variable?
2c. Circle the independent variable and underline the dependent variable in the following
prediction:
IF simple chemicals are the best buffer category, THEN their total buffer range will be the smallest.
3a. Enter your team data in the table. Does your data support
your hypothesis? What about class data?
3b. Which data set (team or class) is more useful when testing
your hypothesis ? Why?
4. How should the pH of the solution being tested in the Acid beaker compare to that in the Base
beaker before any acid or base is added? Why?
5. Why was it of value to include the plot of water in acid and water in base with every
experiment?
6a. What effect did adding HCl have on the pH of each solution?
6b. What effect did adding NaOH have on the pH of each solution?
7. Study the figure below in order to answer the following questions.
a. What is the initial pH of the solution being tested?
b. Use red to color the line indicating the addition of an acid.
c. Use blue to color the line indicating the addition of a base.
d. What is ΔpH for the base?
e. What is ΔpH for the acid?
f. What is the total buffer range?
g. Draw and label a bracket on the figure to indicate the total
buffer range.
Cat. Substance Buffer
Range A B C
14
12 10 8 6 4 2 5 10 15 20 25 30
# drops added
pH
2 Lab Report 3: Buffer Systems
8. In category C, the biological organisms, only the yeast was an entire living organism; the rest
were just parts. Which had the smallest total buffer range? Offer an
explanation why. 9. If a person is suffering both a headache and acid indigestion, which substance would you
recommend? Justify your answer. 10. Indicate the range of initial pH values of the biological organisms by listing the lowest and
highest values for those solutions. Offer an explanation as to why
the initial pH range is not from 0 to 14. 11. Why was the acid and base added in 5 drop increments? Why not in 15 drop increments?
12. Study the following two graphs. Explain the results of each in the context of this experiment.
Drops of what was added? Initial pH: Final pH:
ΔpH: Buffering ability? Explanation of graph: Initial pH: TOP LINE IN GRAPH: Drops of what was added? Final pH: BOTTOM LINE IN GRAPH: Drops of what was added? Final pH: Total Buffer Range: Buffering ability?
14
12 10 8 6 4 2 5 10 15 20 25 30
drops added
pH
14 12 10 8 6 4 2 5 10 15 20 25 30
drops added
pH
Lab 3: Buffer Systems 3
Begin analyzing your data by looking for “outliers”.
Outliers are values which are far from the rest of the data. When outliers exist, you must decide your course of
action: retest or accept the discrepancy based on a valid
scientific explanation. Look at the buffer ranges by category for outliers. List any
you find and decide on your course of action.
Table 2: Initial pH and Buffer Range
Cat. Substance Initial
pH Buffer
Range A B C
Table 3: Initial pH and Buffer Range Cat. Outlier Course
of Action Justify your course of action. A B C
Table 4: Rankings based on pH
Substance Initial pH Rank most acidic 2 3 4 5 6 7 8 9 10 11 least acidic
Table 5: Rankings based on total buffer range
Substance Total Buffer Range Rank greatest change 2 3 4 5 6 7 8 9 10 11 least change
Lab 3: Buffer Systems 9
Lab 3: Evaluating the Effectiveness
Of Buffer Systems
Organisms are often very sensitive to the effect of acids and bases in their environment. They must
maintain a stable internal pH in order to survive, such as in the event of environmental changes.
Many naturally occurring biological, geological, and man-made chemicals are capable of
stabilizing the environment’s pH. Substances that resist changes in pH are buffers. In an aqueous
solution, they form a conjugate of a weak acid and weak base that constitutes a buffer system. In this experiment, your team will be using two pH probes that interface with your computer. You
will measure the effect of both an acid and a base on various solutions. Each team will test water
as well as 3 other substances, one from each of three categories: formulated medicines, simple
chemicals, and solutions from biological organisms. All teams will share their data. In this experiment, you will
• Add an acid to a solution and note the extent to which it resists changes in pH.
• Add a base to a solution and note the extent to which it resists changes in pH.
• Collaborate with other teams to compare the ability of different materials to resist pH
changes.
PROBLEM OF THE DAY
Which of the 3 categories listed below will most effectively minimize pH change?Develop a hypothesis concerning which of
the 3 categories of solutions has the best
buffering ability.
Hypothesis Prediction (If, then):
Null Hypothesis:
Prediction (If, then): Next, determine the independent and
dependent variables in this experiment
based on the following explanations. Record
these on the Lab Report.
Dependent Variable This is what you measure or record. This value
depends upon your manipulation of the
independent variable.
Independent Variable
This variable affects the value of the
dependent variable. It serves as the
“predictor” variable and is the one that is
manipulated by the experimenter.
THREE CATEGORIES OF TEST SOLUTIONS
Item # A = Formulated Medicines B = Simple Chemicals C = Biological Organisms
1 Alka Seltzer vitamin C (ascorbic acid) spinach leaves 2 aspirin gelatin (protein) potato 3 Bufferin (buffered aspirin) artificial salt water chicken egg yeast (unicellular fungus) 4 Tums carbonated drink
10 Lab 3: Buffer Systems
PROCEDURE
Divide your team into two groups. One group
will always use the A probe to test the effects
of adding an acid to a liquid. The other group
will use the B probe to test the effect of
adding a base. One person will also have to
enter data into the computer. NOTE for computer operator (ON CAMPUS)
Your jobs are indicated with this icon .
Setting Up the LoggerPro Program
1. Plug the 2 pH probes into the computer
interface, if not already connected. Open
LoggerPro.2.
Find the word “Latest” located at thetop of the gray data table. Double click
on it. When the window appears, replace
“Latest” with “Control”. Click “OK.”3. Change label of first column heading
by double clicking on “pH 1.” When the
window opens, change “pH 1” to “Acid”,
and click “Done”. Repeat this step to
change “pH 2” to “Base”.4. Adjust the scale for the horizontal X-axis
by double clicking anywhere on the
graph. When the window appears, click
on “Axes Options” tab. In the Y-axis label
window, type in “pH”. Look for the X-axis
information located at the bottom of the
window. Change “Right” value to 30 but
do NOT click “Done”.5. Select the “Graph Options” tab in thesame window. Under “Examine”, check“Legend.” Under “Appearance”, click inthe open square next to “Connect Points”,if it is not already checked. Then click“Done.”6. On the top toolbar, under
“Experiment”, select “Data Collection”.
On the “Collection” tab, select “Events
with Entry”. When the window appears,
type in “Drops” for the “Column Name”
and “#” for “Units. Click “Done”. 7. Open a Word doc and type the properheading:
• first and last name of each team
member, stacked in the upper left
hand corner
• title of this lab (centered 2 spaces
below names)
Establishing Controls
You will test the effects of adding an acid
or base to distilled water (dH2O). 8. Before and after each use of a pH
probe, hold its tip over the large rinse jar.
Thoroughly rinse with distilled water.
Important: Do not let the pH electrode
dry out. Keep it in a 500 mL beaker
containing pH 7 buffer any time that it is
not in use.9. In your kit are two 50 mL beakers, one
labeled acid and the other labeled
base. Group A, add 20 mL of dH2O to
the A beaker. Group B, add 20 mL of
dH2O to the B beaker.10. Rinse the pH probe thoroughly with
distilled water, then hold it in the beaker
to be tested:
• Group A: Hold your probe in the
beaker labeled acid.
• Group B: Hold your probe in the
beaker labeled base.Since the probe is top heavy,
the beaker will fall over if you
don’t hold it. 11.
Click to begin making pH
measurements. Wait for the pH readings
to stabilize (they may bounce up and
down a small amount). Then click
. DO NOT CLICK “STOP” until all the data
has been collected. Should you
accidentally click “Stop”, you must click
again and “Append to Latest”.
