Determination of Concentration of Acetic Acid in Commercial Vinegar

Theoretical Background / Context

• Quantitative analysis deals with the determination of the quantity of the substance to be analyzed. 

Methods of Quantitative Analysis May Be Classified Into:

1. Gravimetric analysis: It depends on isolating and weighing the final product with known pure, stable, and definite form.
2. Instrumental analysis: It depends on measuring some physical properties which change quantitatively with changing the concentration of the sample.
3. Volumetric analysis (Titration): It depends on measuring the volume of standard solution (titrant) used for complete reaction with the sample, which is essential for the quantitative analysis of vinegar by titration.

• Titration is the capacity of the sample to combine with the suitable standard quantitatively through quantitative reaction. 
• A quantitative reaction is a reaction that proceeds forward to produce stable product(s) such as weakly ionizable compounds, e.g. H2O, weak acids & base, sparingly soluble salts (precipitate), complex ion, etc. 

The Types of Quantitative Reactions Can Be:

1. Neutralization Reactions.

1. H2O formation.
2. Displacement: Formation of a weak acid or a weak base.

2. Complexometric reactions.
3. Redox reactions (Electron transfer).
4. Preciptimetric reactions.

• Any sample is a solution of unknown concentration and a Standard is a solution of exactly known concentration. 

The Requirements of Titrimetric Reactions are:

• The reaction must be simple and expressed by a chemical equation.
• A single reaction must occur between the sample and titrant.
• The reaction must be instantaneous (rapid).
• Suitable standard solutions must be available.
• The endpoint should be easily detected.   

Oxidation is loss of electrons and increases in valency number, gain of oxygen or loss of hydrogen

Fe2+ →Fe3+ + e-1

Reduction is gain of electrons and reduction in valency number, loss of oxygen or gain of hydrogen

Fe3+ + e-1→Fe2+ , Fe2+ + 2e-1 → Fe0

Oxidizing agent or oxidant is the substance that gain electrons

Ex: KMnO4, K2Cr2O7, Ce(SO4)2

Reducing agent or reductant is the substance that donates (lose) electrons

FeSO4, Na2S2O3, H2C2O4

Principle Work of Determination of Acetic Acid in Vinegar by Titration

• Vinegar is a common household item containing acetic acid as well as some other chemicals. 
• This vinegar titration 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 through the acetic acid testing method.

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

• By adding the sodium hydroxide, which is a basic solution, to the acetic acid, which is an acidic solution, a neutralization reaction occurs in this vinegar titration lab.
• An indicator known as phenolphthalein, is also added to the vinegar (the acetic acid in vinegar titration lab). 
• This indicator turns the solution to a dark pink when excess NaOH is added to make the solution more basic during the determination of acetic acid in commercial vinegar using NaOH.