The key difference between titration and back titration is that in a titration, we usually add a chemically equal amount of standard solution to the analyte whereas, in a back titration, we add an excess amount of standard solution to the analyte.
Titrations are techniques we mainly use in analytical chemistry to determine the amount of analyte present in a sample. Such analytes include acids, bases, oxidants, reductants, and metal ions.
CONTENTS
1. Overview and Key Difference
2. What is Titration
3. What is Back Titration
4. Side by Side Comparison –Titration vs Back Titration in Tabular Form
5. Summary
What is Titration?
In a titration, a known chemical reaction takes place. Here, an analyte reacts with a standard reagent, which we call the “titrant”. We should use an ideal standard solution in titrations, and it should have several properties such as chemical stability and ability to react rapidly and completely with the analyte.
Sometimes we use a primary standard solution, which is a highly purified and stable solution, as a reference material in titrimetric methods. Then, we can determine the quantity of the analyte if we can find the volume or the mass of titrant that react completely with the analyte.
Figure 01: Apparatus for a Titration
In a titration, the titrant is in the burette, and we add the analyte to the titration flask using a pipette. The reaction takes place in the titration flask. In any titration, the point where the reaction completes (the point of chemical equivalence) is the endpoint of that titration. We can detect the end-point using an indicator which can change its colour at the endpoint. Or else we can use a change in an instrumental response to identifying the endpoint; for example, potential and conductivity.
There are some errors associated with titrations as well. The equivalence point in a titration is the point at which the added titrant is chemically equivalent completely to the analyte in the sample. However, this is a theoretical point, and we cannot exactly measure this experimentally. We can only observe the end-point. Ideally, the end-point is not exactly equal to the equivalence point (titration error), but we try to minimize the gap between the two as much as possible. There can also be human errors associated with this method. Therefore, to minimize these, we often need to repeat a titration at least thrice. Then we can determine the average value.
What is Back Titration?
In a back-titration, we add an excess amount of the standard titrant to the analyte. Then some amount of the standard titrant will react with the analyte, and the excess of it remains in the sample. Here, we can determine this remaining amount of standard reagent using a back-titration.
For example, the amount of phosphate in a sample can be determined by this method. When we add an excess of silver nitrate to a phosphate sample, both will react to give silver phosphate solid. Then we can titrate the excess of silver nitrate with potassium thiocyanate. Therefore, the total amount of added silver nitrate is equal to the amount of phosphate ion and the amount of thiocyanate we use for the back-titration.
What is the Difference Between Titration and Back Titration?
Titration is an analytical technique that we use to determine the amount of an analyte in a sample quantitatively. Back titration method, on the other hand, is an advanced form of a titration technique, which gives more accurate result at the end. However, the key difference between titration and back titration is that in a titration, we usually add a chemically equal amount of standard solution to the analyte whereas, in a back titration, we add an excess amount of standard solution to the analyte.
Furthermore, in the sample of a normal titration, only one chemical reaction takes place. However, in a back titration, there are two chemical reactions taking place in the same sample. Therefore, in a normal titration, we need only one procedure while in a back titration we need to perform two titration procedures. Therefore, this is also an important difference between titration and back titration.
Summary – Titration vs Back Titration
Titrations are very important analytical techniques. There are different types of analytical techniques such as redox titrations, potentiometric titrations, conductometric titrations, etc. Back titration is one such type. In a titration, we usually add a chemically equal amount of standard solution to the analyte whereas, in a back titration, we add an excess amount of standard solution to the analyte. So, this is the key difference between titration and back titration.
Reference:
1. “Titration.” Chemistry LibreTexts, Libretexts, 3 June 2019, Available here.
Image Courtesy:
1. “Acid and Base Titration” By Kengksn – Own work (CC BY-SA 4.0) via Commons Wikimedia