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G-8
REAGENTS AND EQUIPMENT
pH meter and electrodes
two burets
phenolphthalein
standard buffers of pH 4.00 and 7.00
Standardized sodium hydroxide solution (NaOH) (0.2xxx M)
Acetic acid of unknown concentration (CH3COOH) (0.1xxx to 0.4xxx M)
EXPERIMENTAL PROCEDURE
Check to see that the pH meter on your laboratory bench is plugged into the electrical outlet. Your laboratory
instructor will show you how to use the pH meter. Obtain a bottle of acetic acid solution of unknown
concentration from your laboratory instructor. Record the letter code of your unknown on your Observations
Sheet. The concentrations of the unknown solutions are in the range of 0.40 to 0.60 M.
The standardized NaOH solution is to be dispensed from squeeze bottles that are located on the front bench in
the laboratory. NOTE: Record the concentration of the NaOH solution on your Observations Sheet.
Titration of Acetic Acid with Sodium Hydroxide
A. Titration with Indicator Only
Reminder: All buret readings are to be read to 0.01 mL. To read the buret reliably, you must use a meniscus
reading card. If you are uncertain about your buret reading technique, ask your laboratory instructor to check
your readings at the beginning of the laboratory. If most of your readings end in 0 or 5, you are highly unlikely
to be reading the buret correctly.
Note: You are not to adjust your initial reading to 0.00 mL except where indicated in the experimental
procedure. A penalty will be imposed for these errors.
If the acid was an unknown acid, you would do the pH titration curve first in order to choose a suitable
indicator. However, you know that for acetic acid the pH of the equivalence point will be
9.0 therefore, phenolphthalein may be used as the indicator. In this experiment, you will familiarize yourself
with the operation of a pH meter. The change in pH near the equivalence point is dramatic, hence, you should
calculate the approximate volume of sodium hydroxide required to reach the equivalence point (use data from
titrations that employ an indicator). As you approach the equivalence point, you should add the NaOH drop by
drop. In order to determine the approximate volume needed to reach the equivalence point, you are to do the
titrations using the indicator first. These titrations are done in the same way as the titrations in Experiment F.
Get two burets from your instructor. Clean them with water. Rinse one with 2 x 5 mL of the standardized
NaOH solution. Discard this rinse down the drain and then fill the buret with the standardized NaOH and
