What is titration method for assay of aspirin?
Aspirin is a weak acid that also undergoes slow hydrolysis; i.e., each aspirin molecule reacts with two hydroxide ions. To overcome this problem, a known excess amount of base is added to the sample solution and an HCl titration is carried out to determine the amount of unreacted base.
Why is aspirin assay done using back titration?
Using titration it would be difficult to identify the end point because aspirin is a weak acid and reactions may proceed slowly. Using back titration the end-point is more easily recognised in this reaction, as it is a reaction between a strong base and a strong acid.
What is back titration of aspirin?
In the back titration of aspirin, a known excess amount of NaOH is added to the sample solution to ensure that both reactions have gone to completion. Then, an additional titration is performed using HCl to determine the amount of unreacted NaOH.
Which indicator is used in the assay of aspirin?
Phenolphthalein is an indicator because it changes color when all the aspirin has been reacted. This is called the “end point” of the reaction. If one continues adding NaOH after the end point, the solution will turn dark red.
How do you Assay aspirin?
Dissolve ASA sample in 5 ml ethanol 95 % and then add 25 ml of 0.5 N NaOH, the container of the mixture was stoppered and allowed to stand for ½ hour to complete the hydrolysis of ASA. 1-2 drops of bromophenol blue (bpb) indicator was added and the solution was titrated with 0.5 N HCl. The endpoint is pink colorless.
Why is back titration more accurate?
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.
What is the principle of estimation of aspirin?
Principle and Procedure: The amount of aspirin can be determined by brominating using KBrO3-KBr mixture. A definite amount of aspirin is refluxed with NaOH. Then salicylic acid is formed. The excess brominating mixture formed is titrated with standard thio.
What is meant by back titration?
Back titration is a titration done in reverse; instead of titrating the original sample, a known excess of standard reagent is added to the solution, and the excess is titrated.
What is the difference between back and blank titration?
Titration is a volumetric technique used to determine the amount of a substance present in a sample. Back titration is used by adding an excess amount of one reagent/titrant and titrating to determine the excess amount left. That gives the amount of the titrant at the start of the analysis.
How do you perform a back titration?
5 Simple Steps in Back Titration Calculations:
- Determine the amount of C required in the titration.
- Using stoichiometry, find the amount of A that reacted with C in the titration.
- Note that amount of A that reacted with C in the titration = amount of A that did not react with B in the earlier reaction.
What indicator is used to perform the back titration?
Methyl red
Its titrant, HCl, is added in excess, and NaOH is used afterward to back titrate this overadded amount of acid. Methyl red is used as the indicator, changing its color from magenta to yellow at the pH corresponding to the inflection point.
What is the advantage of a back titration?
A back titration is useful if the endpoint of the reverse titration is easier to identify than the endpoint of the normal titration, as with precipitation reactions. Back titrations are also useful if the reaction between the analyte and the titrant is very slow, or when the analyte is in a non-soluble solid.
What is back titration and example?
BACK TITRATION Back titration is a process in which the excess of a standard solution used to consume an analyte is determined by titration with a second standard solution. Example: Determination of acetylsalicylic acid in aspirin. Sometime direct titration of an analyte with a reagent is not FEASIBLE.
What is back titration also known as?
A back titration may also be called an indirect titration.
What is the advantage of back titration?
What is assay titration?
An assay is a type of biological titration used to determine the concentration of a virus or bacterium. Serial dilutions are performed on a sample in a fixed ratio (such as 1:1, 1:2, 1:4, 1:8, etc.) until the last dilution does not give a positive test for the presence of the virus.
What are the steps for back titration?
What is the principle of back titration?
A back titration is a titration method where the concentration of an analyte is determined by reacting it with a known amount of excess reagent. The remaining excess reagent is then titrated with another, second reagent.
What’s a back titration?
A technique in volumetric analysis in which a known excess amount of a reagent is added to the solution to be estimated. The unreacted amount of the added reagent is then determined by titration, allowing the amount of substance in the original test solution to be calculated.