Chemical analysis is essential in studying the composition of substances or materials. There are two types of analysis: qualitative and quantitative. Titration can also be referred to as titrimetry or volumetric analysis.
It is an analytical technique widely used in chemistry laboratories to estimate the concentration of an analyte in a sample solution because it has several applications and advantages. Titration is performed by placing a burette containing a known concentration of a titrant above a conical flask or beaker containing a solute. The titrant is gradually added until the reaction is complete; an indicator usually indicates the endpoint or equivalence point.
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Definition: Precipitation titration is a type of titration in which precipitate forms during the titration procedure. The titrant reacts with the analyte to form an insoluble substance known as a precipitate in precipitation titration. It will continue until all of the analytes have been consumed. |
Precipitation Titration in Chemistry Questions with Solutions
Q1. In the Volhard method, the solution filled in the burette is–
a.) Silver nitrate
b.) Ferric ammonium sulphate
c.) Potassium thiocyanate
d.) Potassium chromate
Correct Answer – (c.) Potassium thiocyanate.
Q2. The indicator used in the Mohr method is–
a.) Fe3+
b.) Fluorescein
c.) Potassium chromate
d.) Eosin
Correct Answer– (c.) Potassium chromate
Q3. Which of the following is/are indicators for precipitation reaction?
a.) Potassium chromate
b.) Silver nitrate
c.) Fluorescein ions
d.) All of the above
Correct Answer – (d.) All of the above
Q4. The precipitation titration in which ____ nitrate is used is called argentometric titration.
a.) Silver
b.) Potassium
c.) Sodium
d.) Ammonium
Correct Answer – (a.) Silver
Q5. Which of the following can be used to detect the endpoint of precipitation titration?
a.) The appearance of excess titrant
b.) The concentration of ions
c.) The disappearance of the reactant
d.) None of the above
Correct Answer – (a.) The appearance of excess titrant and (c.) The disappearance of the reactant.
Q6. What is a precipitation reaction?
Answer. When two solutions containing soluble salts are mixed, a precipitation reaction occurs, resulting in the formation of an insoluble salt. The precipitate is the insoluble salt that emerges from the solution. Precipitation reactions in the solution can aid in determining the identity of various ions.
Q7. What are the various types of precipitation titration?
Answer. Precipitation titrations are classified into three types:
- The Volhard method
- The Fajan method
- The Mohr method
Q8. Explain the Volhard method and the Fajan method of precipitation titration.
Answer. The Volhard method is a type of precipitation titration that is used to determine the bromine, chlorine, and iodine content of a halide by precipitating it with excess silver nitrate and titrating the excess by adding standard potassium thiocyanate (KSCN). It is carried out in an acidic solution.
The Fajan method is a type of precipitation titration that uses the reaction between the produced precipitate and the predictor. Dichlorofluorescein is a solution indicator that acts as an anion.
Q9. How can the endpoint be determined in precipitation titrations?
Answer. The following three traditional methods based on colour indicators can be used to identify endpoints in argentometric titration.
- The formation of coloured precipitate at the endpoint in Mohr’s titration
- The formation of a soluble, coloured complex at the endpoint of Volhard’s titration
- Adsorption of a coloured indicator on the precipitate at the endpoint in Fajan’s titration
Q10. What are precipitation titrations used for?
Answer. The applications of precipitation titrations include the following:
- It is used to determine the concentration of halide ions in a solution.
- It is used to determine the salt content of foods, beverages, and water.
- It is used to make sulphur, thiocyanate, dichromate, and other chemicals.
- It is used in many drugs, including carbromal, KCl infusion, NaCl infusion, and others.
Q11. Which indicators are used in precipitation titration?
Answer. To act as an indicator, a small volume of potassium chromate solution is added, followed by a neutral solution of, say, chloride ions of silver nitrate solution. At the endpoint, the chromate ions interact with the silver ions to form the sparingly soluble, red, silver chromate.
Q12. What is the difference between Mohr, Volhard and Fajans methods?
Answer. The main difference between the Mohr and Volhard methods is that the Mohr method refers to the reaction between silver ion and halide ion in the presence of a chromate indicator, whereas the Volhard method refers to the reaction between excess silver ions and halide ions. Meanwhile, the Fajans method refers to the reaction of silver halide and fluorescein adsorption.
Q13. Explain precipitation titration with the help of an example.
Answer. We can titrate a sample solution with a known concentration of silver nitrate solution to estimate the chloride ion concentration.
The chemical reaction is as follows:
- Ag+ (aq) + Cl– (aq) → AgCl (s)
- During the titration, AgCl forms a white precipitate at the bottom of the conical flask.
- The amount of silver ion used to reach the equivalence point is the same as the initial amount of chloride ion.
- To calculate the number of moles of silver or chloride ion, use n = cV.
Q14. What is the limitation of precipitation reactions?
Answer. There are several limitations to the precipitation titration process as follows:
- The precipitation titration method can only titrate a small number of halide ions.
- Coprecipitation can also occur.
- The endpoint is extremely difficult to assess.
Q15. What is the significance of precipitation titration?
Answer. The significance of precipitation titration includes the following:
- Precipitation titration can provide a quick and accurate analysis result.
- The process of precipitation titration can be automated.
- It does not necessitate any specialised knowledge.
- Mohr’s method of precipitation titration is a simple, direct and accurate method for determining chloride ions.
- Volhard’s precipitation titration method can be used for both direct and indirect halide analysis.
- Fajan’s precipitation titration method can be used with various indicators over a wide range of pH levels.
Practice Questions on Precipitation Titration
Q1. The titration brake of the precipitation curve depends on-
a.) The concentration of the analyte
b.) Solubility product of the precipitate
c.) Temperature
d.) Nature of the indicator
Q2. Which of the following compounds cannot be analysed in the Mohr method?
a.) NaI
b.) KCl
c.) MgBr
d.) CaCl2
Q3. What are the primary titration standards for precipitation?
Q4. What is Mohr’s method of precipitation titration?
Q5. What is the titration principle of precipitation?
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