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I-5
EXPERIMENTAL PROCEDURE:
Preparation of Burets
NOTE:
For this experiment, students will work in pairs. One student will titrated samples of buffer
solution with HCl while the other student performs a similar titration using NaOH.
a)
Using the correct technique, rinse one buret twice with 2 x 5 mL of the HCl solution
discarding each rinse. Fill the buret to a point about the 20 mL mark (do NOT set this
value to 0.00 mL). Record the concentration of this solution on your Observations Sheet.
b)
Using the correct technique, rinse one buret twice with 2 x 5 mL of the NaOH solution
discarding each rinse. Fill the buret to a point about the 20 mL mark (do NOT set this
value to 0.00 mL). Record the concentration of this solution on your Observations Sheet.
NOTE: This experiment is done in pairs. Standardize your pH meter following the
appropriate instructions given on pages 24 to 25.
Part I.
Preparation of the Acetic Acid-Acetate Buffer Solution
1.
Record on your Observations Sheet, the pH of the demonstration solutions of
~0.20 M acetic acid (CH3COOH) and the ~0.20 M sodium acetate (CH3COONa)
2.
Using the automatic dispenser add 50.0 mL of the ~0.20 M sodium acetate solution to a
clean dry 250 mL beaker
3.
Using the automatic dispenser, add 50.0 mL of ~0.20 M acetic acid (CH3COOH) solution
directly into the 0.20 M CH3COONa solution prepared above. Allow the solution to stand
for 10 minutes to reach room temperature, then determine the pH of this acetic acid-sodium
acetate buffer solution and record this initial value on your Observations Sheet.
Part II.
Effect of the Addition of a Strong Acid to Deionized Water
1.
Using a pH meter, record the pH of the 25 mL of deionized water in a 100 mL beaker.
2.
Add 2 drops of 0.20 M HCl to the water (above) and again measure and record this pH.
Part III.
Study of the Acetic Acid-Acetate Buffer Solution
A.
Determine the Effect of Dilution on a Buffer Solution.
1.
Add 25.0 mL of the buffer solution to a 400 mL beaker. Re-measure and record the pH of
this buffer solution. (The pH should be the same as the initial measured in Step 3 above.)
2.
Add 225 mL of deionized water to the buffer sample. This solution will be a 1/10 dilution
of the original buffer solution. Measure and record the pH of this diluted buffer.
