Key Difference – Acid-Base Titration vs. Redox Titration
In general, titrations are used to determine the concentration of an unknown solution (analyte). The most commonly used two titrimetric methods are acid-base titrations and redox titrations. The key difference between acid-base titrations and redox titrations is the nature of the reaction that happens between the titrant and the analyte in the titration. In acid-base titrations, a neutralization reaction takes place and in redox titrations, a redox reaction takes place (an oxidizing reaction and a reduction reaction). The use of indicators is the most commonly used method of determining the endpoint of the reaction.
What is an Acid-Base Titration?
In acid-base titrations, an acid (acidic titrations) or a base (basic titrations) is used as the titrant. Examples of acids used in acidic titrations are H2SO4, HCl, or HNO3. Mostly used basic titrants are NaOH, K2CO3 or Na2CO3. Acid-base titrations can be classified as follows depending on the strength of the acid and the base.
- Strong acid – strong base titrations
- Strong acid- weak base titrations
- Weak acid – strong base titrations
- Weak acid – weak base titrations
In most of the acid-base titrations, indicators are used to determine the end point of the reaction. Different indicators are used depending on the type of the titration as mentioned above.
What is a Redox Titration?
A redox titration involves a redox reaction. Redox reaction has two reactions; an oxidation reaction and a reduction reaction. Both oxidation and reduction processes take place at the same time where allowing us to determine the completion of the reaction. This is also known as the end point of the titration. This can be determined in several ways; using indicator electrodes, redox indicators (the indicator produces a different color at oxidation-reduction state), and non-redox indicators (indicator produces a color when an excess amount of titrant is added).
What is the difference between Acid-Base Titration and Redox Titration?
Nature of the reaction:
Acid-Base Titration: An acid-base titration involves a neutralization reaction between the analyte (the solution with the unknown concentration) and the acidic or basic titrant.
Redox Titration: A redox reaction involves an oxidation and reduction reaction between the analyte and the titrant. There is no such a rule that component oxidizes and which one reduces. Either analyte or the titrant oxidizes, and the remaining component reduces accordingly.
Determination of the end point:
Acid-Base Titration: In general, a pH indicator, a pH meter or a conductance meter is used to determine the end point of an acid-base titration.
Redox Titration: The most commonly used methods of determining the end point of a redox reaction are using a potentiometer or a redox indicator. But, most frequently either the analyte or the titrant produces a color at the endpoint. So that, additional indicators are not required in those cases.
Examples:
Acid-Base Titration:
| Type | Reaction (Indicator) |
| Strong acid – strong base titration | HCl + NaOHàNaCl + H2O(Phenolphthalein /Methyl orange) |
| Strong acid – weak base titration | HCl + NH3à NH3Cl (Methyl orange) |
| Weak acid – strong base titration | CH3COOH + NaOHà CH3COONa + H2O (Phenolphthalein) |
| Weak acid –weak base titration | CH3COOH + NH3àCH3COO–+NH4+(No suitable indicators) |
Redox Titration:
2 KMnO4 + 5 H2C2O4 + 6 HCl → 2 MnCl2 + 2KCl + 10 CO2 + 8 H2O
(+7) (+3) (+2) (+4)
In the above reaction, permanganate is reduced while oxalic acid is oxidized. When the reaction completes, the purple color of permanganate changes into colorless.
KMnO4 + 5FeCl2 +8HCl → 5FeCl3+MnCl2+KCl+4H2O
(+7) (+2) (+3) (+2)
Image Courtesy:
1. Titration of weak acid with strong base By Quantumkinetics (Own work) [CC BY 3.0], via Wikimedia Commons
2. “Winkler Titration Prior Titration” by Willwood [CC BY-SA 3.0] via Commons
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