大学化学实验报告
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大学化学实验报告
Title: Determination of the Concentration of Acetic Acid in
Vinegar by Titration
Introduction:
Acetic acid, also known as ethanoic acid, is a weak acid that is
commonly found in vinegar. Determining the concentration of
acetic acid in vinegar is an important task as it allows us to
understand the quality of the vinegar and compare it to industry
standards. In this experiment, titration will be used to determine
the concentration of acetic acid in a given sample of vinegar.
Materials and Methods:
1. A burette
2. A 50 mL volumetric flask
3. A 100 mL beaker
4. Sodium hydroxide (NaOH) solution of known concentration
5. Phenolphthalein indicator
6. Vinegar sample
7. Distilled water
Procedure:
1. Measure 20 mL of vinegar sample using a graduated cylinder
and transfer it to the 50 mL volumetric flask.
2. Fill the volumetric flask to its graduation mark with distilled
water, ensuring thorough mixing of the solution.
3. Use a pipette to transfer 10 mL of the diluted vinegar solution to
a clean 100 mL beaker.
4. Add 3 - 4 drops of phenolphthalein indicator to the beaker.
5. Fill the burette with NaOH solution of known concentration. 6. Slowly add NaOH solution to the vinegar solution in the beaker
while gently swirling the mixture.
7. Continue adding NaOH solution until a light pink color that
persists for at least 30 seconds is observed in the solution.
8. Record the volume of NaOH solution used in the titration.
9. Repeat steps 3-8 two more times for accuracy.
10. Calculate the average volume of NaOH solution used.
Results:
The volume of NaOH solution required to neutralize the vinegar
sample was recorded as follows:
Trial 1: 17.5 mL
Trial 2: 17.2 mL
Trial 3: 17.3 mL
Average volume of NaOH solution used = (17.5 + 17.2 + 17.3) / 3
= 17.33 mL
Calculations:
The balanced equation for the reaction between acetic acid and
sodium hydroxide is as follows:
CH3COOH + NaOH → CH3COONa + H2O
From the equation, we can deduce that 1 mole of acetic acid reacts
with 1 mole of sodium hydroxide.
The molar concentration of acetic acid in the vinegar sample can
be calculated using the formula:
Molar concentration of acetic acid = Molar concentration of NaOH
× Volume of NaOH used / Volume of vinegar sample
Assuming the molar concentration of the NaOH solution is 0.1 M,
and the volume of NaOH solution used is 17.33 mL (0.01733 L),
and the volume of the vinegar sample is 20 mL (0.02 L), the molar
concentration of acetic acid in the vinegar sample can be calculated
as follows:
Molar concentration of acetic acid = 0.1 M × 0.01733 L / 0.02 L =
0.0866 M
Conclusion:
The molar concentration of acetic acid in the vinegar sample was
determined to be 0.0866 M. This concentration indicates the
quality and strength of the vinegar sample. By comparing this
value with industry standards, it is possible to determine the
authenticity and purity of the vinegar product.
