Set up your titration apparatus: Erlenmeyer flask,
ring stand, buret and buret clamp, as shown in the picture
below.
Prepare the titration apparatus: Rinse the buret
with tap water, then deionized water, then with a few mL of
standard NaOH solution. Record the concentration of standard NaOH
solution. Fill the buret with NaOH solution and record the initial
(starting) volume by reading the volume at the lowest point
of the meniscus. The volume on the picture below reads
27.35 mL. Note that the numbers read from low to high as
the level decreases. The buret should be read to ±0.01 mL.
Prepare the unknown analyte. Weigh three empty Erlenmeyer
flasks. Using a volumetric pipet, add 25.00 mL of acetic acid
to the flasks and weigh the flasks again. You will
need to record all significant figures shown in the
balance. Add 3 drops of phenolphthalein indicator to
each flask.
Titrate the unknown analyte. Begin the titration by
adding the sodium hydroxide solution from the buret to the
flask. Swirl to mix thoroughly as you add NaOH
solution. The solution initially will be colorless, but a
pink color will begin to appear and persist longer as you continue
adding NaOH. Occasionally use a wash bottle to rinse droplets
from the sides of the flask and the tip of the buret. The
endpoint for this titration is a very faint pink color that
persists for more than 15 seconds. A dark pink color indicates that
you have added too much sodium hydroxide. At the endpoint,
record the buret volume to the nearest 0.01 mL. Perform the
titration a minimum of three times until you have three precise
titrations.
Calculations: Determine the volume of titrant (NaOH)
from the difference between the initial (VNaOH, initial)
and final (VNaOH, final) volume of NaOH in the buret
(VNaOH = VNaOH final – VNaOH
initial). Multiplying by the known concentration of NaOH
(MNaOH) gives moles of NaOH (MoleNaOH,
Equation 2). Reaction (1) shows a 1:1 ratio of moles of acid and
base, so MoleNaOH equals moles of acid
(MoleCH3COOH) when they are neutralized (Equation 3).
The mass of CH3COOH (MassCH3COOH) and percent
by mass of CH3COOH (% CH3COOH) can then be
found since the sample mass (Massvinegar) was carefully
weighed (Equation 4 and 5).
Trial 1
Trial 2
Trial 3
Molarity NaOH, M
0.4936
0.4936
0.4936
Molar mass (CH3COOH), g/mol
60.052
60.052
60.052
Mass of Empty flask, g
Mass of flask + vinegar, g
Mass of vinegar, g
(Use the same value for all three trials)
VNaOH Initial, buret reading, mL
VNaOH Final, buret reading, mL
VNaOH, mL
Moles NaOH = moles CH3COOH
Mass CH3COOH
Percent CH3COOH in vinegar