Introduction

Vinegar is a common household item containing acetic acid as well as some other chemicals. This experiment is designed to determine the molar concentration of acetic acid in a sample of vinegar by titrating it with a standard solution of NaOH.

CH₃COOH_(aq) + NaOH_(aq) -> CH₃COONa_(aq) + H₂O_(l)

By adding sodium hydroxide, which is a basic solution, to the acetic acid, which is an acidic solution, a neutralization reaction occurs. An indicator known as phenolphthalein is also added to the vinegar. This indicator turns the solution to a dark pink when excess NaOH is added to make the solution more basic. Thus, when the solution turns light pink, this indicates that it has successfully been neutralized.

The amount of NaOH used to standardize the vinegar can then be used to determine the amount of acetic acid in the vinegar as they are both at a 1:1 ratio as seen in the above equation. Thus, the moles of NaOH used to neutralize the acid must equal the number of moles of acetic acid present in the vinegar.

Purpose

The purpose of this vinegar titration investigation is to experimentally determine the molar concentration of acetic acid in vinegar through a titration of vinegar using a standard solution of sodium hydroxide and vinegar. This will investigate the question is NaOH vinegar?

Hypothesis

The molar concentration of acetic acid in a 100mL sample of vinegar is 0.883mol/L. (calculations below)

Apparatus

Suction Pump                          250ml Erlenmeyer Flasks                               Beaker
Retort Stand                            100mlvolumetric Flask                                   Electronic Balance
Burette                                    10ml Volumetric Pipette                                Funnel
Burette Clamp

Materials

Vinegar                       Sodium Hydroxide                   Oxalic Acid                  Indicator

Procedure

• Determine the approximate molar concentration of vinegar from the information provided on the bottle. Density of acetic acid is 1.06 g/mL.
• Based on you calculations, prepare 100 mL of a standard solution sodium hydroxide solution of an appropriate molar concentration.(calculations on page 3)
• Standardize the sodium hydroxide by titrating three 10 mL samples of a solution of 0.50 M oxalic acid.

Image 1: Setup of the apparatus during the titration.

• Once standardized, use the sodium hydroxide solution to titrate three 10 mL samples of the vinegar.
• Clean up you lab solution.

Observations

Titration with sodium hydroxide and oxalic acid

Constants

• 10mL (±0.01mL) of oxalic acid used for each trial
• 3 drops of indicator were used for each trial
• Air pressure = 103.28 (±0.005kPa)
• Temperature = 22.5^oC (±0.05 ^oC)
• All three trials were successful as the solutions turned a light pink color.

Titration with sodium hydroxide and vinegar

Constants

• 10mL (±0.01mL) of vinegar used for each trial
• 3 drops of indicator were used for each trial
• Air pressure = 103.28 (±0.005kPa)
• Temperature = 22.5^oC (±0.05 ^oC)
• All three trials were successful as the solutions turned a light pink color.

Calculations and Data Processing

Analysis

The purpose of this investigation was to determine the molar concentration of acetic acid in vinegar through a titration of vinegar using a standard solution of sodium hydroxide. This experiment showed that the concentration of acetic acid is 0.44mol/L (±3.87%). However, the exact value of the amount of acetic acid present in a 100mL sample of vinegar is 0.883mol/L. The 50% error in this lab can be accounted for through flaws within the procedure of the experiment.

The reactions that occurred during the experiment were neutralization reactions, meaning that the moles of acid equaled the moles base at the end of the experiment. This factor was used to calculate the molar concentration of the acetic acid by applying it to the formula ‘moles = concentrations x volume’. This series of calculations also contributed towards the uncertainty associated with the final answer as each step approximately doubles the % uncertainty.

Errors

In regards to errors that affected the results of this experiment, there are many that have contributed to the total 50% error. One major factor that affected the result of this experiment was the strength of the sodium and sodium hydroxide. If either of these substances is left open in the atmosphere, they begin to lose their strength. During the experiment, the sodium and sodium hydroxide were both left open to interact with the environment for some time. Thus, the final answer did not match the theoretical value accurately because the strength was weakened, meaning that the numbers used to calculate the molar concentration were not as accurate.

To prevent this error from affecting the results of the experiment, one should attempt to keep the sodium and sodium hydroxide in an enclosed environment at all times, thus limiting the time it has to interact with the atmosphere.

In addition, the equipment used could have also contributed to the error as all pieces of apparatus have an uncertainty attached to it. These uncertainties are then applied to calculations in order to keep up the amount of uncertainty associated with the amount of material used. This uncertainty was found to be ±3.87% for all of the experiments. This value includes both uncertainties regarding those that applied when the solutions were made (e.g., the uncertainty of the mass balance that was used to measure the amount of sodium that was needed to make the sodium hydroxide) and the transfer of the solution from one instrument to another. These uncertainties can be reduced by using more accurate equipment, for example, a more accurate mass balance. Also, limiting the transfer of solution from one container to another will also reduce the amount of error.

Human judgement also accounts for some of the error in this experiment as the person performing the experiment was required to read off many measurements from the pipette and burette. This error can be reduced by always ensuring that readings are always made at eye level and that the same person taking the readings is constant as judgement varies with each person.

Conclusion

In conclusion, this experiment found the molar concentration of acetic acid NaOH titration in vinegar to be 0.44mol/L. However, this value was 50% inaccurate due to errors that occurred while conducting the investigation. This titration of vinegar experiment highlights the challenges and importance of precision in lab procedures, particularly when working with sodium hydroxide and vinegar.

William Anderson (Schoolworkhelper Editorial Team)

William completed his Bachelor of Science and Master of Arts in 2013. He current serves as a lecturer, tutor and freelance writer. In his spare time, he enjoys reading, walking his dog and parasailing. Article last reviewed: 2022 | St. Rosemary Institution © 2010-2024 | Creative Commons 4.0

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