The Biodiesel Lab

vegetable oil


The Biodiesel Lab is an activity developed by Learning Undefeated to help students explore the process of titration and its role in creating biodiesel fuel.

Biodiesel fuel is created from vegetable oil through a chemical process called transesterification. Unfortunately, the transesterification reaction is very sensitive to the presence of free fatty acids that are prevalent in vegetable oils. In order for the transesterification process to be efficient, the acids must be neutralized. The levels of free fatty acids, and therefore the appropriate levels of base needed, can be determined through a process called acid/base titration. A titration is a way of determining the concentration of a substance by adding a known concentration of a reagent until a certain effect is seen.

In this activity, your students will perform an acid/base titration to determine the molarity of free fatty acids in a waste vegetable oil solution.

Lab Objectives

Upon completion of The Biodiesel Lab, students will be able to:

  • Understand the process of titration; perform two (2) titrations
  • Calculate the molarity of a solution based upon its equivalence point
  • Analyze the results of the completed titrations
  • Understand how these results are used to produce biodiesel fuels
  • Apply their results to neutralize a large quantity of vegetable oil

Background Information

Biodiesel is an alternative fuel for vehicles that use petroleum or diesel fuel. Using biodiesel would reduce dependence on the nonrenewable resource of petroleum or other fossil fuels, because it is made from more renewable sources such as vegetable oils and animal fats.

pH Scale

The pH scale measures the potential amount of hydrogen present in a solution. It is based on the amount of hydrogen ions, measured in moles per liter. A pH from 0-7 is considered an acid, 7 is neutral, and 7-14 is basic.

Acid/Base Titration

The process of titration works to neutralize free fatty acids present in both regular and wast vegetable oils. Being on the opposite end of the pH scale, a base will balance out an acid. It is necessary to know the exact amount of base needed to neutralize the ffas in the vegetable oil in order to determine the concentration of that specific oil. This allows usage of the correct solution on a larger, more practical, scale for biodiesel production. By adding an indicator, we can see how much base is needed to neutralize ffas in different vegetable oils. For this lab, we use turmeric, a natural indicator.

A weak acid, such as those present in the vegetable oil, reacting with a strong base, such as NaOH, will yield a solution with a pH greater than 7.

Equivalence point: the point at which equal amounts of the reactants have reacted.

End point: when we see a color change from the indicator solution. Ideally, this is close to the equivalence point of the reactants.


This is the process performed with neutralized acid (in this case, vegetable oils and the corresponding amount of base) with alcohol. This reaction creates glycerol, which settles to the bottom, and esters, or biodiesel.

Pre-Laboratory Engagement

Biodiesel is a great alternative for fuel. But why do we need biodiesel?

Have students research alternative fuel use compared with fossil fuel use. What are the different types of fuels available? Are there standards to fuel production and usage? Why don’t we all use biodiesel?

Laboratory Activity

MdBioLab has purchased a new generator that can run on biodiesel fuel. Biodiesel is a renewable form of energy that is manufactured from the natural oils found in vegetables. It is used in diesel engines and provides a cleaner burning alternative to petroleum- based diesels.

Biodiesel is created from vegetable oil through a chemical process called transesterification. This process uses sodium hydroxide, a very strong base, to convert the vegetable oil into a combustible liquid. The transesterification process separates the oil into two products, methyl esters (biodiesel fuel) and glycerol (a valuable by-product used to make soap and other skin care products).

Unfortunately, the transesterification reaction is sensitive to the presence of free fatty acids, which occur more prevalently in waste vegetable oil that has degraded over time. Luckily, the same chemical that is used to catalyze the reaction which produces biodiesel, sodium hydroxide, can also be used to eliminate or “neutralize” these acids.

Waste Vegetable Oil (WVO) Inexpensive
High levels of Free Fatty Acids

Straight (pure) Vegetable Oil (SVO)
Low levels of Free Fatty Acids

Titration process to determine levels of ffa’s Fatty Acids


Bottom Layer Glycerol Used for Soap

The levels of free fatty acids can be determined through a process called acid/base titration. A titration is a way of determining the concentration of a substance by adding a known concentration of a reagent to it until we see an effect. In our case, we will add a known concentration of sodium hydroxide to the free fatty acids contained in vegetable oil until we see a color change (this color change is due to a change in pH which we can observe by adding a pH indicator). When the mixture’s color has been changed (from yellow to bright pink), then it has reached its equivalence point and the free fatty acids have been neutralized.

2NaOH + [free fatty acid]àNa2[neutralized free fatty acid] + 2H2O
We need your help to determine the molarity of free fatty acids in the waste vegetable oil. To do so you

will need to find the equivalence point for the waste vegetable oil.

Post-Laboratory Engagment

Have students design their own biodiesel production plant. Using the concentration of vegetable oil found in the lab, determine the larger scale amounts needed for daily production based on the customers your plant would be producing for.


  • Skill Level: Advanced
  • Focus: Chemistry, organic chemistry
  • Time: 60 – 70 minutes
  • Restrictions: 24 students maximum

NGSS Standards Alignment

HS-PS1: Matter and its Interactions

TEKS Alignment










Key Words

Biodiesel, transesterification, acid, base, methyl esters, glycerol, free fatty acid, NaOH, titration, vegetable oil, Filet O’ Fish, renewable, energy, neutralize, catalyze, pH, indicator, turmeric, mols, molarity

Additional Resources
Facts about biodiesel fuel

Calculating Molarity
Website on how to calculate molarity

Reaction of Esters (AP)
Mechanism for transesterification

900 Miles on Renewable Energy 


Stoichiometry calculator