Title: The Bicarbonate Buffer
Introduction - The bicarbonate buffer is one of the buffers that helps control blood pH. This
experiment will show you how this buffer system works.
Materials:
 Red Cabbage Juice Indicator (already
prepared)
 2 150 mL beakers
 Dropper Bottle of Vinegar



Baking soda
Scupula or plastic spoon
Clear soda pop (Sprite or 7-Up, for example)
What you have in each beaker is a solution of anthocyanin (made from boiling red/purple cabbage
leaves), which is an acid-base indicator. It turns blue in the presence of high pH and pink in the
presence of low pH. In between, it turns a variety of colors. Right now, it should be a light purple, which
indicates a pH of roughly 7.
Procedure:
1. Add approximately 50 mL of the cabbage solution to each beaker.
2. Add half a teaspoon of baking soda to one of the beakers. You should see the color change towards
green. That is because the bicarbonate ion in the baking soda is a base. The green color is
anthocyanin’s reaction to the higher pH.
3. Label this beaker “Buffer” and the other beaker “Control.”
4. Use the tablespoon to add one tablespoon of Sprite to the “Buffer” beaker that you just put the baking
soda in. Use that tablespoon to stir the solution. Continue to add Sprite one tablespoon at a time (stirring
in between) until the color of the solution roughly matches the color of the solution in the other beaker
(the one you haven’t added anything to). This sample now has a mixture of an acid (carbonic acid from
the Sprite) and base (bicarbonate from the baking soda). This is the bicarbonate buffer.
5. You now have samples, each at roughly the same pH. One has a buffer solution, the other does not.
6. Take the eyedropper and add two drops of vinegar to the beaker labeled “Control” that does not have
the buffer. Swirl the glass to mix the vinegar in the solution. Record: Note the color.
7. Next, repeat step 6 with the “Buffer” beaker. Record: Note the color change, if any.
8. Alternatively add two drops of vinegar to each solution, swirling in between. Continue until each
solution changes color. Record how many drops were added to each solution. Record: Compare how
quickly the bicarbonate buffer solution changes colors to how quickly the other solution changes
colors.
9. Clean everything up.
10. Respond to the following:
1. Explain any differences you saw between how quickly each solution changed color.
2. How does this relate to what we’ve discussed about buffers?
3. Why would buffers be helpful in the body? Your answer should refer to the term homeostasis
4. Create a flow chart of boxes illustrating each step of this activity and the color reaction of each
beaker. Labels should help a reader understand what is happening. It should be colored.
5. What is alkalosis?
6. What could lead to alkalosis in the body?
7. What is acidosis?
8. What could lead to acidosis