Define the preparation of Titrimetry or Acid-Base Titration

I. PURPOSE OF THE EXPERIMENT

In this experiment the acid content of vinegar solution was determined by acid-base titrimetry. It was …….g / L acetic acid. This experiment will also introduce the concept and technique of titration, quantitative analysis and weak acid and strong base titration.
(A) The NaOH solution is standardized with standard H2SO4 solution using methyl orange indicator.
(B) After this standardization the sodium hydroxide solution becomes a secondary standard. It is then titrated with unknown vinegar solution using phenolphthalein indicator.

II. INTRODUCTION

It is customary to express acid content of vinegar in terms of acetic acid % (w/v) and acid content of wines in terms of tartaric acid % (w/v), regardless of the presence of other acids. Most wines contain less than 1% (w/v) acid expressed as tartaric acid. Whereas most vinegars contain 5% (w/v) acid expressed as acetic acid. Acid in vinegar solution is generally determined by titrimetric method using standard NaOH solution. Sodium hydroxide solution reacts with both sulphuric acid and acetic acid solution as in the following chemical reactions.
Sodium Hydroxide + Sulphuric Acid Sodium Sulphate + Water

2NaOH (aq) + H₂SO₄ (aq) Na₂SO₄ (aq) + 2H₂O (l)

(Mole Ratio of NaOH : H₂SO₄ = 2 : 1 )

Sodium Hydroxide + Acetic Acid Sodium Acetate + Water

NaOH (aq) + CH₃COOH (aq) CH₃COONa (aq) + H₂O (l)

(Mole Ratio of NaOH : CH₃COOH = 1:1 )

CH3COOH is also called Ethanoic Acid (Geneva System, IUPAC method)

CH3COONa is also called Sodium Ethanoate.

III EXPERIMENTAL

3.1 Chemicals........Standard H₂SO₄…….M, NaOH solution, Vinegar solution, Methyl orange and Phenolphthalein indicator.

1.2    tEquipment…Titration set.

1.3     Procedure

1. First Titration: Standardization of NaOH solution

1. The standard (approx 0.05M) sulphuric  acid was placed in the burette.
2. 10 mL of the NaOH solution were transferred into a 125 mL conical flask with the aid of a pipette.

3. 1-2 drops of methyl orange indicator were added and titrated with the previously standardized sulphuric  acid. Color changed from orange to yellow

4. The titrations were repeated until duplicate determinations agree within 0.1mL of each other.
   
2.    Second titration: Analysis of a diluted vinegar solution

1. The vinegar solution was placed in the burette.
2. 10 mL of the standard NaOH solution were transferred into a 125 mL conical flask with the aid of a pipette.
3. 1-2 drops of Phenolphthalein indicator were added and titrated with the Vinegar solution.
The endpoint is colourless
4.    The titrations were repeated until duplicate determinations agree within 0.1mL of each other.

IV. RESULTS and DISCUSSION

1. Molarity of NaOH solution                0.115M

2. Molarity of CH₃COOH solution                0.06M

3. g / L (mass of acetic acid in 1 L of Vinegar solution)     3.6g/L   

4. Acetic acid content of vinegar solution as (% w/v).     0.36 (% w/v)

DISCUSSION

1.     Does the vinegar you analyzed comply with the legal content of acetic acid?

Yes, the vinegar comply with the legal content of acetic acid

2.    If vinegar can be kept in a plastic bottle.

The vinegar can be kept in plastic bottle because it contains less than 1% of acid

CONCLUSION

The acetic acid content of vinegar solution was determined. It was 3.6g/L acetic acid approximately 0.36 (% w/v)Acetic acid content of vinegar solution in this experiment.

SAFETY

1. Phenolphthalein: This chemical is an organic dye that is toxic in large quantities. It should be handled with the usual precautions: do not ingest, get on your skin or eyes, and do not spill into the laboratory environment.

2. Sulphuric acid: Avoid contact of acid with skin or clothing. Dilute sulphuric acid is used in this experiment, and is less hazardous than concentrated H₂SO₄. If H₂SO₄ is spilled on your skin or clothing, remove clothing immediately and use plenty of cold water to rinse skin.