Note: The weak acid/conjugate base pair you will use is acetic acid/acetate ion. Using white
vinegar, which is 5% acetic acid, you will prepare an acetic acid/acetate ion buffer as
described below. It is important that you:
Keep the pH paper clean
Avoid air bubbles when transferring solutions by plastic pipits
Use clean toothpicks and stir the solutions after adding each drop of buffer
Avoid cross contamination of toothpicks.
Part I: Preparation of the solutions and materials:
1. Make acetic acid buffers: Place 2mL of white vinegar in each of wells A1, A6, B1, and
B6 of the 24-well plate. Add to each well, 4 drops 6M NaOH from the auxiliary chemicals
dropper bottle and stir using a clean toothpick.
2. Dilute 6M HCl to 0.1M HCl by placing 2mL of distilled water in well D1. Add to it, add 1
drop 6M HCl from the auxiliary dropper bottle. Stir with a clean toothpick.
3. Dilute 6M NaOH to 0.1M NaOH by placing 2mL of distilled water in well D6. Add 1 drop
6M NaOH from the auxiliary dropper bottle. Stir with a clean toothpick.
4. Cut 18 of the wide range pH test strips into thirds. This will yield 54 test strips of
approximately 1 cm each in length.
5. Thoroughly rinse the labeled NaOH and HCl pipets from the auxiliary bag with distilled
water. Then remove as much water from the pipits as possible by squeezing them
multiple times, tapping their tips onto paper towels, and forcefully swinging the pipits
through the air with a downward motion while squeezing their bulbs.
In part II, you actually begin the experiment itself. You will use the data tables in your worksheet and follow the instructions going drop by drop.
Part II: Adding different concentrations of acid and base to a buffer:
1. Prepare Data Tables 1 through 6, similar to those that follow, for recording pH and color
data.
2. Add only one drop of dilute HCl from well D1 into the buffer in well A1. Measure the pH
by dipping a 1cm strip of pH paper into the solution. Record the color in Data Table 1.
Repeat this process for a total of 16 drops added to well A1. Remember to stir the
solution when adding each additional drop of HCl.
3. Add only one drop of dilute NaOH from well D6 into the buffer in well A6. Measure the
pH by dipping a 1cm strip of pH paper into the solution. Record the color in Data Table 2.
Repeat this process for a total of 16 drops added to well A6. Remember to stir the
solution when adding each additional drop of NaOH.
4. Add only one drop of 6M HCl directly from the auxiliary dropper bottle into the buffer in
well B1. Measure the pH by dipping a 1cm strip of pH paper into the solution. Record
the color in Data Table 3. Repeat this process for a total of 5 drops added to well B1.
Remember to stir the solution before adding each additional drop of HCl
5. Add only one drop of 6M NaOH directly from the auxiliary dropper bottle into the buffer in
well B6. Measure the pH by dipping a 1cm strip of pH paper into the solution. Record
the color in Data Table 4. Repeat this process for a total of 5 drops added to well B6.
Remember to stir the solution before adding each additional drop of NaOH
Table 1:
Add 0.1 M HCl
Drops pH Color of Paper
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
