Acid Value Determination in Oils & Phenol Properties

Acid Value Determination in Oils: Principle and Procedure

Here's an explanation of the principle and procedure involved in determining the acid value of an oil sample:

Principle

The acid value of an oil sample is a measure of the amount of free fatty acids present in the oil. The principle of the acid value determination is based on the reaction between the free fatty acids in the oil and a strong base, such as potassium hydroxide (KOH). The reaction is as follows:

RCOOH (Free Fatty Acid) + KOH → RCOOK (Potassium Salt) + H₂O

Procedure

Here's the step-by-step procedure for determining the acid value of an oil sample:

1. Apparatus

• 250 mL Erlenmeyer flask
• Burette
• Pipette
• Volumetric flask
• Phenolphthalein indicator

2. Reagents

• Potassium hydroxide (KOH) solution (0.1 N)
• Phenolphthalein indicator
• Oil sample

3. Preparation of KOH Solution

• Weigh 5.6 g of KOH and dissolve it in 1 L of distilled water.
• Standardize the KOH solution by titrating it against a known amount of oxalic acid.

4. Determination of Acid Value

• Weigh 10-20 g of oil sample into a 250 mL Erlenmeyer flask.
• Add 50-100 mL of ethanol or isopropanol to the flask to dissolve the oil.
• Add 2-3 drops of phenolphthalein indicator to the flask.
• Titrate the solution with 0.1 N KOH solution until the pink color of the indicator persists for 30 seconds.
• Record the volume of KOH solution used (V).

5. Calculation of Acid Value

Calculate the acid value using the following formula:

Acid Value = (V * N * 56.1) / W

Where: V = Volume of KOH solution used in mL N = Normality of KOH solution W = Weight of oil sample in grams 56.1 = Molecular weight of KOH

Expression of Results

The acid value is expressed as milligrams of potassium hydroxide (KOH) required to neutralize 1 gram of oil.

Phenol: Properties, Preparation, and Reactions

What are Phenols?

Phenols are a class of organic compounds that contain a hydroxyl (-OH) group attached to a benzene ring. They are also known as carbolic acids.

Acidity of Phenol

Phenol is a weak acid, with a pKa value of around 10. It is less acidic than carboxylic acids but more acidic than alcohols. The acidity of phenol is due to the ability of the hydroxyl group to donate a proton (H+ ion).

Methods of Preparation

Here are three methods of preparing phenol:

1. Cumene Process

This is the most common method of producing phenol. It involves the reaction of cumene (isopropylbenzene) with air to produce phenol and acetone.

C₆H₅CH(CH₃)₂ + O₂ → C₆H₅OH + (CH₃)₂CO

2. Dow Process

This method involves the reaction of benzene with sodium hydroxide (NaOH) to produce phenol.

C₆H₆ + NaOH → C₆H₅OH + NaH

3. Raschig Process

This method involves the reaction of benzene with hypochlorous acid (HOCl) to produce phenol.

C₆H₆ + HOCl → C₆H₅OH + HCl

Reactions of Phenols

1. Bromination

Phenol reacts with bromine to produce 2,4,6-tribromophenol.

C₆H₅OH + 3Br₂ → C₆H₂Br₃OH + 3HBr

2. Nitration

Phenol reacts with nitric acid to produce 2,4,6-trinitrophenol (picric acid).

C₆H₅OH + 3HNO₃ → C₆H₂(NO₂)₃OH + 3H₂O

3. Esterification

Phenol reacts with carboxylic acids to produce phenolic esters.

C₆H₅OH + RCOOH → C₆H₅OCOR + H₂O