Measuring the amount of acetic acid in vinegar investigatory project

Explanation:

Abstract

Measuring the Amount of Acetic Acid In Vinegar by Titration with an Indicator Solution. The goal of this project is to determine the amount of Acetic Acid in different types of vinegar using titration with a coloured pH indicator to determine the endpoint.

Theory

Vinegar is a solution made from the fermentation of ethanol (CH3CH2OH), which in turn was previously fermented from sugar. The fermentation of ethanol results in the production of acetic acid (CH3COOH). There are many different types of vinegar, each starting from a different original sugar source (e.g., rice, wine, malt, etc.). The amount of acetic acid in vinegar can vary, typically between 4 to 6% for table vinegar, but up to three times higher (18%) for pickling vinegar. In this project, we will determine the amount of acid in different vinegars using titration, a common technique in chemistry. Titration is a way to measure the unknown amount of a chemical in a solution (the titrant) by adding a measured amount of a chemical with a known concentration (the titrating solution). The titrating solution reacts with the titrant, and the endpoint of the reaction is monitored in some way.

The concentration of the titrant can now be calculated from the amount of titrating solution added, and the ratio of two chemicals in the chemical equation for the reaction. To measure the acidity of a vinegar solution, we can add enough hydroxyl ions to balance out the added hydrogen ions from the acid.

The hydroxyl ions will react with the hydrogen ions to produce water. In order for a titration to work, we need three things:

1. a titration solution (contains hydroxyl ions with a precisely known concentration),

2. a method for delivering a precisely measured volume of the titrating solution, and

3. a means of indicating when the endpoint has been reached.

For the titrating solution, we’ll use a dilute solution of Sodium Hydroxide (NaOH). Sodium Hydroxide is a strong base, which means that it dissociates completely in water. So for every NaOH molecule that we add to the solution, we can expect to produce a hydroxyl ion. To dispense an accurately measured volume of the titrating solution, we will use a burette. A burette is a long tube with a valve at the bottom and graduated markings on the outside to measure the volume contained in the burette.

The burette is mounted on a ring stand, directly above the titrant solution (as shown in the picture). Solutions in the burette tend to creep up the sides of the glass at the surface of the liquid. This is due to the surface tension of water. The surface of the liquid thus forms a curve, called a meniscus. To measure the volume of the liquid in the burette, always read from the bottom of the meniscus. In this experiment, we will use an indicator solution called phenolphthalein. Phenolphthalein is colourless when the solution is acidic or neutral.

When the solution becomes slightly basic, Phenolphthalein turns pinkish, and then light purple as the solution becomes more basic. So when the vinegar solution starts to turn pink, we know that the titration is complete.

Materials Required:

To do this experiment we will need the following materials and equipment:

 Vinegar, three different types.

 Distilled water

 Small funnel

 0.5% Phenolphthalein solution in alcohol (pH indicator solution)

 0.1 M sodium hydroxide solution

 125 mL Conical flask

 25 or 50 mL burette

 10 mL graduated cylinder

 Ring stand

 Burette clamp

Calculation:

 Required amount of sodium hydroxide (NaOH) can be calculated using the following formula which is added in 1st image.

 The acetic acid content of a vinegar may be determined by titrating a vinegar sample with a solution of sodium hydroxide of known molar concentration (molarity).

CH3COOH + NaOH --> CH3COONa + H2O

(Acid) + (Base) --> (Salt) + (Water)

At the end point in the titration stoichiometry between the both solution lies in a 1:1 ratio.

Strength of acid in vinegar can be determined by the following formula:

Strength of acetic acid = MCH3COOH × 60

Observation

Observation is added in 3rd image.

Result

 Strength of acetic acid in household vinegar = 40.5 g/L.

 Strength of acetic acid in wine vinegar = 72 g/L.

 Strength of acetic acid in fruit vinegar = 48 g/L.