The key difference between total acidity and titratable acidity is that total acidity refers to the sum of titratable and non-titratable acidity, whereas titratable acidity refers to the volatile acid content of a sample that can be titrated using a base.
The terms total acidity and titratable acidity are closely related to each other because titratable acidity is included in the total acidity of a particular sample.
CONTENTS
1. Overview and Key Difference
2. What is Total Acidity
3. What is Titratable Acidity
4. Total Acidity vs Titratable Acidity in Tabular Form
5. Summary – Total Acidity vs Titratable Acidity
What is Total Acidity?
Total acidity can be described as a measure of the total number of hydrogen ions that occurs in a substance in the form of fixed and volatile acids. Therefore, this type of acidity typically includes potential hydrogen ions that can get released and hydrogen ions that are already in the solution. This is also known as the total acid number or TAN.
It can be measured by the amount of potassium hydroxide in milligrams that the sample needs to neutralize the acid content in a gram of the solution. It can be described as a significant quality of measurement in crude oil. For example, this value can determine the potential for corrosion of crude oil refinery. Generally, it is the naphthenic acid content in crude oil. It is also known as naphthenic acid corrosion.
The three major methods of determining the total acidity include potentiometric titration, color-indicating titration, and spectroscopic method. In the potentiometric titration, the sample is dissolved in toluene and propanol in the presence of a trace amount of water, and then the resulting solution is titrated with alcoholic potassium hydroxide. There, we need a glass electrode and a reference electrode that is immersed in the solution to be connected to a potentiometer. This potentiometer gives a reading in millivolts that we can plot against the titrant volume. The graph gives the endpoint at total acid content.
The second common method is color-indicating titration, in which a pH indicator should be used, such as phenolphthalein. A burette is used to add the titrant to the sample where the permeant color change of the solution gives the endpoint of the solution, which indicates the total acid content.
The third method is the spectroscopic method. It gives fast, accurate readings that use mid-near infrared spectroscopy for this purpose. The method is based on absorptions and emissions, where the endpoint gives the total acidity.
What is Titratable Acidity?
Titratable acidity of a sample can be described as the amount of strong base required to titrate the sample. Moreover, pH indicators and titratable acids can be defined as indicators to quantify the content of organic acids and their salts in samples such as fruits. Both these factors also affect gel formation. Most importantly, titratable acidity is the volatile acid content of a given sample, and it does not include any fixed acid substances.
There are different ways of determining the titratable acidity of a sample, but the most common method is a titration with an alkali solution. The most common alkali solution used is sodium hydroxide, along with the phenolphthalein indicator. The equation for the calculation is as follows:
Titratable acidity % = [N(normality of titrant) x E(volume of titrant) x EQ(equivalent weight)] / [W(mass of the sample) x 1000]
What is the Difference Between Total Acidity and Titratable Acidity?
Total acidity and titratable acidity are two important factors in the analysis of different samples for their acid content. The key difference between total acidity and titratable acidity is that total acidity refers to the sum of titratable and non-titratable acidity, whereas titratable acidity refers to the volatile acid content of a sample that can be titrated using a base.
Below is a summary of the difference between total acidity and titratable acidity in tabular form for side-by-side comparison.
Summary – Total Acidity vs Titratable Acidity
Total acidity is a measure of the total number of hydrogen ions that occurs in a substance in the form of fixed and volatile acids, while titratable acidity of a sample is the amount of strong base required to titrate the sample. The key difference between total acidity and titratable acidity is that total acidity refers to the sum of titratable and non-titratable acidity, whereas titratable acidity refers to the volatile acid content of a sample that can be titrated using a base.
Reference:
1. Hakim, Samim. “Titratable Acidity.” Viticulture and Enology, 4 Apr. 2018.
Image Courtesy:
1. “Titration Curves of 20 Amino Acids Organized by Side Chain” By Lvwarren at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia