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by Maud Essen and Chug from www.biofuel-uk.net/
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Why We Titrate to Make Biodiesel
Why We Use Indicators to Titrate
All About Indicators
Phenolphthalein is the industry standard for titrating fats and oils to determine the percentage of FFAs they contain. It must be handled with care because it is toxic. Phenolphthalein changes from colorless to pink.Turmeric is by no means new as an indicator and references to it can be found in chemistry texts. Because turmeric is readily available in the spice section of many grocery stores and lacks the toxicity of phenolphthalein, its use as an indicator is on the rise. Turmeric changes color from yellow to orange/red at a pH close to that of phenolphthalein. Until recently, phenol red was frequently utilized for biodiesel titrations because it is available in countries where there are pool or spa shops. But because it changes color at a more acidic pH, experience has shown that phenol red is not suitable for use in biodiesel titrations unless the oil is known to titrate below 3.
What Is a "Blank Titration" and Why Do I Care?
When you perform a "Blank Titration" you add titration indicator solution to alcohol and then add NaOH/KOH tester solution one drop at a time. Once the indicator just starts to turn color in the blank titration you know all of the acid in the alcohol has been neutralized or eliminated.
After you neutralize the acid in the alcohol, you know that the titration will measure just the acid in the oil itself. Following a "Blank Titration", you can simply add the oil to the neutralized alcohol and proceed to perform the titration itself.
Turmeric indicator solution starts to change color between pH 7.4 (above neutral) and pH 8.5 (alkaline). For our purposes as biodiesel homebrewers, this is accurate enough. With some alcohol, adding just one or two drops of NaOH/KOH tester solution to a "Blank Titration" may achieve a color change but with other alcohol it may take seven or eight drops.What Does It Mean to "Neutralize" Free Fatty Acids (FFAs) to pH 8.5
When we titrate oil in solution with alcohol, we conduct a chemical reaction between the FFAs in the oil and the NaOH or KOH in the solution. This chemical reaction makes soap, which is alkaline.
Chemists have figured out that when ALL the FFAs have been turned into soap, the pH of the solution will rise to pH 8.5. They refer to this process as neutralization, as the FFAs (acids) have been eliminated. But keep in mind that this neutralized solution is alkaline (pH 8.5), NOT chemically neutral (pH 7).
Indicators that can tell us when a solution has a pH around pH 8.5 are most appropriate for biodiesel homebrewers. That is why turmeric and phenolphthalein are suitable, as they change color at pH levels that are close enough to pH 8.5 for our purposes. Turmeric contains a yellow pigment called curcumin that is yellow at pH 7.4 and orange to red at pH 8.6. Phenolpthalein is colorless up to pH 8.3 when it turns pink, through to deep red at pH 9.
Chemists before us figured out what a titration's pH is supposed to be and the experiences of thousands of biodiesel homebrewers have confirmed this in practice. So if you use an indicator (pH strips, bromthymol blue, etc.) that requires you to compare the color of your results against a scale, be sure that you titrate to pH 8.5 NOT to pH 7.
Indicator Color Change Persists 30 Seconds During Titrations
So if one person's turmeric indicator starts yellow and changes into an orange-rose and someone else's starts greenish-yellow and changes into orange or red (as in this example picture at the bottom of the page), it doesn't matter. What matters is that the color has changed from the original yellow color to the same colour as your blank titration and stayed that way for 30 seconds, do some tests with your turmeric and observe the shade or colour it actually changes to when blanked.
This means that you shouldn't "push" a turmeric or phenolphthalein titration to yield a particular shade or intensity of color. As soon as the color changes and persists for 30 seconds, the titration is complete. The key is to use a consistent approach from titration to titration, it should be noted that when titrating with turmeric the titration mixture has a cloudy look to it and is not clear like phenolpthalien.First, make a 0.1% NaOH/KOH tester solution- 1 gram of catalyst (NaOH or KOH) dissolved in 1 litre of distilled water as per:- Step 1: Make Reference Tester Solution here
Making a Turmeric Indicator Solution
Performing a "Blank Titration"
How to titrate WVO
Collaborative Biodiesel Tutorial - Copyright 2005