Acid Value Calculator

Acid value (or acid number) measures the amount of free fatty acids in oils and fats, expressed as mg KOH per gram of sample. It's crucial for determining oil quality, rancidity levels, and suitability for biodiesel production.

Dissolve the oil sample in ethanol, add phenolphthalein indicator, and titrate with standardized KOH solution until a pink endpoint persists for 30 seconds. Always run a blank titration with the same solvents.

Typically 0.1 N KOH solution is used for most samples. For samples with very low acid content, 0.01 N may be more appropriate, while high-acid samples may require 0.5 N solution.

Free fatty acid percentage is calculated by multiplying the acid value by the molecular weight of the predominant fatty acid and dividing by twice the molecular weight of KOH (112.2).

Use 282.5 g/mol for oleic acid (most common), 256.4 g/mol for palmitic acid, 284.5 g/mol for stearic acid, or 200.3 g/mol for lauric acid, depending on your oil's fatty acid profile.

The blank titration accounts for any alkalinity in the solvents or impurities that might consume KOH. This ensures accurate results by subtracting background consumption from the sample titration.

For edible oils, acid values should be <0.6 mg KOH/g. For biodiesel feedstock, values <2.0 mg KOH/g are preferred. Higher values indicate rancidity or require acid pretreatment before processing.

Temperature affects both the solubility of the sample and the endpoint detection. Perform titrations at room temperature (20-25°C) for consistent results and ensure the sample is completely dissolved before titration.