Name: ________________ Lab Partner’s Name:_______________
Date:____________
Acid-Base Buffer Lab
Period:___________
How does our blood maintain a certain pH when we eat acidic or basic foods?
Last week we were introduced to acids and bases. We learned about common foods and
household items that are acidic or basic. If we eat acids (such as lemons, soda, , oranges,
pineapples, tomatoes, beef, carrots, vinegar, etc…) and bases (salt, potatoes, eggs, asparagus,
almonds, etc..), then how does our blood maintain a specific pH? Blood pH is regulated to stay within
the narrow range of 7.35 to 7.45, making it slightly alkaline (basic). Blood that has a pH below 7.35 is
too acidic, whereas blood pH above 7.45 is too alkaline.Human blood contains a buffer system. If this
buffer system was absent from our blood, then eating acidic or basic foods would cause the pH to
swing too high (alkalosis) or too low (acidosis), and the results could be deadly.
This lab will demonstrate the buffering solution found in your blood.
Our blood cannot tolerate a drastic shift in pH. It's a good thing, then, that human blood
contains a bufffer of carbonic acid, H2CO3, (like in soda) and sodium bicarbonate, NaHCO3.(baking
soda which is a base) This buffer regulates drastic shifts in the pH of our blood.
Variables and Hypothesis: (The hypothesis states how the independent variable affects the
dependent variable.)
Independent Variable-______________________
Dependent Variable-_________________________
Control-________________________________
Hypothesis- If___________________________________________________,
then____________________________________________________________.
Materials:
Sodium Bicarbonate (Baking Soda
which has a pH of9 )
Lemon Juice (which has a pH of 2.5)
Cabbage Juice
Test tubes
Test tube rack
Beaker
Stirring rod
Eye dropper
Water (assumed pH of 7)
Timer
Procedure:
----PART 1:----- Unbuffered Solutions
Test Tube #1:
1.Place 10 ml of cabbage juice in a test tube. Note the color.
2.Add 5 drops of lemon juice (citric acid). Note the new color and record the pH in the data table.
3.Save this test tube & solution for comparison in Part 2 of this lab.
Test Tube #2
4.Place 10 ml of cabbage juice in a test tube. Note the color and record.
5.Add 5 drops of water. Note the new color and record the pH in the data table.
6.Save this test tube & solution for comparison in Part 2 of this lab.
Test Tube #3
7.Place 10 ml of cabbage juice in a test tube. Note the color and record.
8.Add 5 drops of Sodium Bicarbonate solution (baking soda). Note the new color and record the pH in
the data table.
9.Save this test tube & solution for comparison in Part 2 of this lab.
------PART 2-------*
The Beaker : Buffered System
1.To make a buffer solution, pour 50 mL of Sodium Bicarbonate solution NaHCO3 (baking soda) into
a beaker. Swirl the buffer solution and gently blow exhaled breath (Carbon Dioxide or 𝐶𝑂2) into the
solution for at least 2 minutes.
2.Add 10 mL of cabbage juice indicator to the buffer solution in the beaker. Note the color and
compare it to the known pHs of the solutions in the test tubes Record your findings in the data table.
3.Add 3 drops of Citric Acid (lemon juice) to the buffer solution and record your observations. What
happened to the color of the solution as you dropped the citric acid into it? Record your observations
in the data table..
4.Continue to add citric acid drop by drop, counting the drops (swirl to mix) until the color matches the
unbuffered solution from step 2 in part #1 or you reach 50 drops. How many drops did you use? Does
it ever get to the color of the first test tube Record your observations.
*If time permits, repeat Part 2 (steps 1-4) to increase accuracy and precision by completing 3
trials of the buffer system. No need to reproduce your control panel from Part 1.
Data and Observations
Table #1
Test Tube #
pH
color
Acid, Neutral, or Base?
Test Tube #1
Test Tube #2
Test Tube #3
Table #2: Buffer System Beaker
color
observations
Before you
add any citric
acid
After you add
3 drops
At the end
*If you have time to do 2 more trials, draw a new data table#2 for each trial
Acid or a Base?
Discussion Questions: (Answer these questions in paragraph form and analyze/discuss the
above data and observations. Your discussion should be a minimum of 3 paragraphs)
Questions to discuss in your discussion section
1. What is a buffer?
2. How does it work? (What happens when an acid reacts with a base?)
3. Why would we need a buffer system in our bodies? What would happen if the buffer system
in our blood no longer worked?
4. Did our experimental buffer system work? Give evidence.
5. Exhaled breath contains CO2. This carbon dioxide reacted with the water in the beaker to
form carbonic acid, H2CO3. Write the chemical reaction and make sure it is balanced.
6. What sources of error were there in our experiment?
7. How might have these sources of error affected our results?
8. How would you improve this experiment and reduce the sources of error?
Conclusion:

Summarize the experiment.

Revisit your hypothesis and tell whether the data/observations prove or disprove your
hypothesis.