Main Difference – Acid-Base Titration vs Redox Titration
Titration is a widely used laboratory technique for the quantification of chemical analytes by means of their concentration. This is performed using a set of special apparatus. In general, it is performed between two liquid solutions whose identities are known. In order to find the unknown parameter, which is the concentration of the analyte (in most cases), the concentration of the other solution must be known. To avoid confusion in the process, the solutions are labelled by different names and placed in respective apparatus. Therefore, the solution with known concentration is called the ‘titrant’, and it is usually placed in the burette. The solution with unknown concentration/ the solution under investigation is called the ‘titrand’ or analyte and is usually placed in the titration flask. A chemical indicator is often used to find the equivalence point of the titration, and the indicator is generally added to the solution in the titration flask. An Indicator is sensitive to the medium it is in and is able to change colour accordingly. This is the basis for any type of titration. The two main types of titrations are acid-base titration and redox titration. The main difference between acid-base titration and redox titration is that acid-base titration involves an acid and a base whereas the redox titration involves two redox species.
What is Acid-Base Titration
This is a type of titration where the two species involved are an acid and a base. The reaction type between the species is an acid-base neutralisation reaction, with the formation of water as a by- product. As a general rule, the base is kept in the titration flask and the acid is added to the burette. The reaction that occurs between the two species is trickled down to the reaction between H+ ions and OH- ions. What is taken at the end is a volume measurement from the burette. Therefore, the volume required from the titrant to completely react with a known amount of volume of the titrand is what is recorded. These numbers are then related to the chemical equations with their stoichiometry, and the concentration of the unknown solution can be determined.
An acid-base indicator is usually added to the base solution in the titration flask in order to determine the equivalence point/ end point of the titration. An acid-base indicator is able to show one colour in the base medium and another colour in an acidic medium. After a complete neutralization, when an extra drop of the acid is added from the burette to the base in the titration flask, the medium turn from basic to acidic. The colour of the indicator also changes, and the titration is thus brought to a halt. When a strong acid is titrated with a strong base, the equivalence point is at pH=7, but the pH curve changes if the acids/ bases used are weak instead.
Titration methyl orange
What is Redox Titration
Redox titrations are another type of titration that conforms to the general organization of a titration. However, the reaction between the two species, in this case, is a redox reaction. This means the reaction takes the form of an oxidation/reduction reaction, while one species gets oxidized, the other species gets reduced. And this determines the feasibility of a redox reaction taking place. When a certain species gets oxidized, it releases electrons which in turn raises its oxidation number. And when a species get reduced, it accepts electrons, and its oxidation number decreases. Therefore in a redox reaction, the amount of electrons that is circulated remain constant, meaning that the electrons which are released by the oxidizing species need to get accepted by the reducing species, depending on the stoichiometry of the reaction.
Some redox species act as self-indicators such as MnO4– ions which lose its purple colour upon its reduction to Mn2+. In other cases, such as reactions where I2 molecules are involved, starch is used as an indicator as it produces a colour due to the formation of a complex with Iodine. In general, the ‘d’ block elements such as Fe2+/Fe3+, Cr3+/Cr6+, Mn7+/Mn2+ commonly take part in redox reactions as they have variable oxidation numbers.
Color of iodometric titration mixture before (left) and after (right) the end point
Difference Between Acid-Base Titration and Redox Titration
By definition
In an acid-base titration, the species involved are acids and bases.
Redox titrations are titrations that take place among redox species.
Reaction between the species
In an acid-base titration, the species take part in a neutralization reaction forming water molecules.
In redox titrations, the species react through oxidation and reduction reactions
The use of indicators
Weak acids and weak bases are used as indicators for acid-base titrations.
Some redox species act as self-indicators and for most cases special redox indicators are used.
Occurrence
Acid-base titrations are more common as it can take place between any form of acid and base/ weak and strong.
Redox titrations are commonly seen among the ‘d’ block elements.
Image Courtesy:
“Acidobazna titracija 002″ by Lara Djelevic – Own work. (CC BY 4.0) via Commons
“Iodometric titration mixture” by LHcheM – Own work. (CC BY-SA 3.0) via Commons
