Determination of the Concentration of Acetic Acid in Commercial Vinegar

Description

• Vinegar is a common household item containing acetic acid and other chemicals.
• This experiment aims to determine the molar concentration of acetic acid in vinegar by titrating it with a standard solution of sodium hydroxide (NaOH).

Reaction Equation

• The neutralization reaction that occurs during titration is represented by the following chemical equation:
  $\text{CH}_3\text{COOH}(aq) + \text{NaOH}(aq) \rightarrow \text{CH}_3\text{COONa}(aq) + \text{H}_2\text{O}$
• In this reaction, acetic acid (CH₃COOH), an acid, reacts with sodium hydroxide (NaOH), a strong base.

Indicator

• An indicator known as phenolphthalein is utilized in this experiment.
• Phenolphthalein turns the solution dark pink when there is an excess of NaOH, indicating that the solution has become more basic.

Aim

• The aim of this experiment is to experimentally determine the molar concentration of acetic acid in vinegar.

Learning Objectives

• To accurately determine the concentration of acetic acid in vinegar using volumetric analysis, utilizing the neutralization reaction of acetic acid with sodium hydroxide.
• To acquire the correct techniques for performing titration.

Tools and Materials

• Burette
• Distilled water
• Pipette
• Standard solution of sodium hydroxide (0.216 M)
• Commercial vinegar
• 250 mL conical flask
• Phenolphthalein indicator

Procedure

1. Clean the burette:
       - Rinse the burette with distilled water and discard the rinse water.
       - Rinse the burette with 5 mL of NaOH standard solution and discard that as well.
2. Fill the burette:
       - Use a funnel to fill the burette with sodium hydroxide (NaOH) standard solution (0.216 M) until it reaches its zero point.
3. Prepare vinegar solution:
       - Use a pipette to transfer 10 mL of vinegar into a clean 250 mL conical flask.
4. Add indicator:
       - Add approximately two drops of phenolphthalein (Ph.Ph.) indicator solution into the vinegar flask.
5. Perform titration:
       - Start the titration by slowly draining sodium hydroxide from the burette, drop by drop, while swirling the flask.
       - Continue until the solution changes from colorless to a faint permanent pink, then record the end point.
6. Record volume:
       - Record the final volume of sodium hydroxide used in the titration.
7. Repeat:
       - Repeat the above steps two additional times, recording the final volume of sodium hydroxide each time. Then calculate the average volume used.

Calculations

Data Collection

• Molarity of standard NaOH(aq) (M₁): 0.2160 M
• Molarity of acetic acid (analyte) (M₂): --------------- M
• Reported mass percent of acetic acid in vinegar: 5.0%
• Volume of acetic acid used in each trial (V₂): 10 mL

Molarity Calculation Equation

• By substitution in the following equation:
  $M_1V_1 = M_2V_2$
• Rearranged to find M₂:
  $M_2 = \frac{M_1V_1}{V_2}$
• Substitute the known values to calculate M₂:
    - Result: M₂ = --------------- M

Percentage of Acetic Acid in Vinegar Calculation

• To calculate the percentage of acetic acid in the vinegar solution, use the formula:
    \text{% acetic acid in vinegar solution} = \left( \frac{\text{mass of acetic acid}}{\text{mass of vinegar solution}} \right) \times 100

Mass Calculation of Acetic Acid

• The mass of acetic acid can be calculated using:
  $\text{Mass of acetic acid} = \left( \frac{M_2 \times V_2}{1000} \right) \times \text{molecular weight of acetic acid}$
    - Where the molecular weight of acetic acid is 60 g/mol.

Mass Calculation of Vinegar Solution

• The mass of vinegar solution can be calculated using:
  $\text{Mass of vinegar solution} = \text{density of vinegar} \times \text{volume of vinegar}$
    - Given: Density of vinegar = 1 g/cm³
    - Volume of vinegar = 10 cm³
    - Result: Mass of vinegar solution = 10 g

Final Percentage Calculation

• By substitution in the percentage formula:
    \text{% acetic acid in vinegar solution} = \left( \frac{\text{mass of acetic acid}}{10} \right) \times 100
    - Result: % acetic acid in vinegar solution = ---------------%