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Chemistry 121: Experiment 7
Buffer Solutions in the Blood
OBJECTIVES
Part A: Review the definition of a buffer solution.
Part B: Observe the effect of strong acid on proteins found in blood serum.
Part C: Learn how to prepare a buffer solution and observe the effect of strong acid on the buffer solution’s pH.
BACKGROUND INFORMATION
To properly function, humans need to maintain a blood pH between 7.35 and 7.45. A blood pH below 7.35 results in a condition called acidosis which causes headaches, fatigue, confusion, tremors, and in extreme cases can be fatal. Blood pH above 7.45 causes alkalosis resulting in confusion, muscle spasms, nausea, and can be equally fatal.
Metabolism of proteins, starches, and sugars result in waste products that must be excreted from the body. These waste products are transported through your blood to the kidneys. Because some of these waste products are acidic, a buffer system is necessary to maintain your blood’s pH. For example uric acid is a waste product from the metabolism of proteins, and lactic acid is produced during metabolism in your muscles.
A buffer solution requires a weak acid and its conjugate base to both be present in significant concentrations. The human body uses carbonic acid to create a buffer because it is naturally exists in equilibrium with water in the bloodstream and the dissolved CO 2 generated as a result of metabolism:
H 2 O( l ) + CO 2 ( aq ) H 2 CO 3 ( aq )
Being a weak acid, carbonic acid partially ionizes when dissolved in water to produce hydronium ions and its conjugate base, bicarbonate:
H 2 CO 3 ( aq ) + H 2 O( l ) H 3 O+( aq ) + HCO 3 – ( aq )
Since the equilibrium constant for this reaction (Ka) is approximately 3 x 10–^4 , only 1 out of every 3000 carbonic acid molecules ionizes and becomes the conjugate base. Therefore, to obtain sufficient buffer capacity at the optimal pH, additional bicarbonate ions are released into the bloodstream by the kidneys.
Student Name:
Lab 7: Blood Buffer Solution: Student Worksheet
Please complete each section of this worksheet by watching the linked video for each section, filling out the data table, and answering any questions. You may use this as a template and modify the document so it contains your answer. Then you can convert this file to a pdf and submit it in canvas.
All videos in this lab will be linked below. Videos are also compiled in this youtube playlist: https://www.youtube.com/playlist?list=PLvetE9fWAB85tEHvAq1ih36ERJRCEOLOV
A. What is a buffer?
A buffer solution maintains a pH by neutralizing small amounts of added acid or base. It
contains a combination of a weak acid and a salt of its conjugate base.
- Place an X by the pair of compounds that will make a buffer solution when combined.
______ H 2 CO 3 & CO 2 _______ NH 4 +^ & NH 3 ________ H 2 CO 3 & C 2 H 4 O
- Write the chemical formula of the conjugate base of each of the following compounds:
a. C 2 H 4 O 2
b. H 2 PO 4 –^
- Write the chemical formula of the conjugate acid of the following compounds:
a. SO 32 –^
b. HCO 3 –^
Table 2 : Butterfly peaflower Acid Base indicator
Acidic pH < 7 (^) Neutral pH 7 Alkaline pH > 7
Watch the following video and record your observations in Table 3 about the preparation of the buffer solution. Once the solution is prepared it will be tested with a strong acid, hydrochloric acid (HCl). Record the pH of the solution after each addition of acid in Table 4.
Video: https://youtu.be/b3e1HXrM_IE
Table 3: Observations of simulated blood buffer preparation.
Volume of water, H 2 O
pH of water
Observations: What happens to the pH of the solution as carbon dioxide, CO2, is exhaled into the solution?
pH of carbonic acid solution
Mass of sodium bicarbonate, NaHCO 3
Final pH of buffer solution
Table 4: The addition of hydrochloric acid (HCl) to water and to a H 2 CO 3 /NaHCO 3 solution.
Drops of HCl added
pH beaker containing H 2 CO 3 /NaHCO 3
pH beaker containing Only H 2 O
Total Number of drops of acid required to reach the buffer capacity of water
Total Number of drops of acid required to reach the buffer capacity of carbonic acid and bicarbonate buffer
- Graph the data collected in Table 4. The x axis will represent the drops of acid added and the y axis will represent the pH of the solution. Graph both the data for water and for the carbonic acid & bicarbonate solution. Students may either: - Graph in excel using the template provided, then embed the graph below or turn in separately. - Or graph on a sheet of graph paper (template provided as well) then convert to a pdf file to either embed below or turn in separately
<insert graph here, or turn in as a separate file>
- Interpret your observations and analysis (graph) of the pH data:
a. Did the water or the H 2 CO 3 /NaHCO 3 solution act as a buffer when acid was added dropwise?
b. What behavior observed during the experiment indicates a solution acts as a buffer?
c. Compare the number of drops of acid that was required to reach the buffer capacity of the water and the buffer solution.
Watch the following video and record your observations in Table 5 as a strong base, sodium hydroxide (NaOH) is added to both water and the buffer solution.
Video: NaOH addition to the buffer solution: https://youtu.be/1drNTwbCL
