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Titration Methods- Principle, Acid-Base Titration, Redox titrations, Precipitation titrations, Complexometric titrations, Practice Problems and FAQs

Titration Methods- Principle, Acid-Base Titration, Redox titrations, Precipitation titrations, Complexometric titrations, Practice Problems and FAQs

When baking a cake, you add baking powder to make a soft bread right??? A precise amount of all ingredients including baking powder is required here because less or more will not produce good bread.

Calculating the amounts or concentration of aqueous substances using an aqueous solution containing a known quantity of an reacting substance using a colour change is called titration. When titration is performed, a volume of titrant and analyte are mixed in order to calculate the concentration value of the unknown from the known. To obtain accurate results, the exact amount of titrant should be measured. Let's learn more about titration in this content.

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Table of Content

  • Principle
  • Acid-Base Titration
  • Redox Titrations
  • Precipitation Titrations
  • Complexometric Titrations
  • Practice Problems
  • Frequently Asked Questions – FAQs

Principle

Titrations are based on the principle that chemical substances react with each other in terms of their equivalent weight or one equivalent weight of any substance reacts with one equivalent of another substance.

Types of Titrations

When aims and processes are considered, there are numerous forms of titration. However, in quantitative chemical analysis, the most typical titration types are

  1. Acid-Base titration
  2. Redox titration
  3. Precipitation titration
  4. Complexometric titration

Acid-Base Titration

It's a method for determining the concentration of an unknown material (acid/base) by comparing it to the concentration of a known substance (acid/base).

Analyte: A chemical whose concentration is unknown.

Titrant: A chemical whose concentration is known.

Standard solution: Solution whose concentration is known exactly

Equivalence point: The stage of titration where the concentrations of titrate and titrant are chemically equivalent is known as the equivalence point.

End point: An endpoint is a titration stage that signifies that the titration has been completed by a change in the colour of the solution.

In titration, a known volume of one of the solutions (an acid or a base) is placed in a flask and the other is placed in a burette to determine the volume required for full neutralization.

Experiment

For example, in oxalic acid and sodium hydroxide base titration, a known volume of oxalic acid whose concentration is known is taken in a conical flask and NaOH is added slowly from burette, and the solution is titrated . The added indicator phenolphthalein in oxalic acid is initially colourless. But once the reaction is complete, the solution turns pink. This indicates the completion of the reaction. After identifying the endpoint, we may determine the unknown base concentration.

Redox Titrations

An oxidation-reduction process is another name for the redox titration. The chemical reaction in this kind of titration is carried out by an electron transfer in the reactive ions of aqueous solutions. The following titrations are named for the reagent employed in them:

  1. Permanganate Titrations
  2. Dichromate Titrations
  3. Iodometry and Iodimetry Titrations

Permanganate Titrations

The potassium permanganate is utilized as an oxidizing agent in this titration. Sulphuric acid that has been diluted is used to maintain it. The equation is shown below.

2KMnO4+3H2SO4K2SO4+2MnSO4+3H2O+5O

Additionally, the solution is colourless before to the endpoint. Oxalic acid, ferrous salts, hydrogen peroxide, oxalates, and compounds that can be oxidized can all be estimated using potassium permanganate. While potassium permanganate solution is usually standardized before use with a standard solution of oxalic acid.

Dichromate Titrations

Potassium dichromate is an another oxidizing agent like potassium permanganate that can be utilized in titrations in an acidic media. Sulphuric acid that has been diluted is used to keep the medium acidic. The potential equation reads:

K2Cr2O7+4H2SO4K2SO4+Cr2(SO4)3+4H2O+3[O]

It is mostly utilized for the estimation of iodides and ferrous salts.

Iodimetric and iodometric titrations:

Both titrations use free aqueous iodine.The free iodine reacts with a standard sodium thiosulphate solution. Iodine oxidizes sodium thiosulphate to tetrathionate and get reduced iodide ions. The difference ies in the way free iodine is obtained.

I2 + 2 S2 O3 2-                    →              2I- + S4 O6 2-

Iodimetric titration:

This titration uses natural free iodine to estimate the concentration of reducing agents. But as free iodine is less soluble in water and more volatile, it is mixed with enough KI to make a complex KI3 which is water soluble and stable.

The triiodide react with any reducing agents Starch is used as an indicator. Starch forms a deep blue or violet colour with iodine.

I2 + 2 S2 O3 2-          →                  2I- + S4 O6 2-

The disappearance of the colour will be the end point in iodimetric iterations.

Iodometric titration:

This titration is uses liberated iodine to estimate the concentration of oxidizing agents. In the presence of strong acids, oxidizing agents like chlorate oxidizes iodide to liberate free iodine. The amount of free iodine liberated is equivalent to the the oxidizing agent present. The free iodine can be titrated against sodium thiosulphate with starch indicator. The concentration of the oxidizing agent is estimated indirectly from the iodine liberated.

2 KI → 2 K+ + 2I-

2I- + Oxidizing agent → I2 + Reduced substrate

I 2 + 2 S2 O3 2- → 2 I- + S4 O6 2-

The disappearance of the colour will be the end point in iodimetric iterations.

Precipitation Titrations

Precipitation titration is based on the insoluble precipitate that forms when the two reacting chemicals come into contact. For instance, a reaction occurs that produces a white precipitate of silver thiocyanate or silver chloride when the solution of silver nitrate is added to a solution of ammonium thiocyanate or sodium chloride.

 

AgNO3+NaClAgCl+NaNO3AgNO3+NH4CNSAgCNS+NH4NO3

 

The exact end point can be fixed with the help of chromate indicator in the case of silver halide and with ferrous ions in case of thiocyanate reactions.

Complexometric Titrations

A metal forms a complex with ligands. An undissociated complex is produced at an equivalence point during a complexometric titration. Complexometric titrations to estimate the concentration are done by four methods:

  1. Direct titration - colour of the complex is used as the self indicator
  2. Back titration - Adding excess ligand and titrating unreacted ligand with another titrant.
  3. Replacement titration- by reacting the complex with another metal
  4. Alkalimetric titration - titrating the acid liberated during the complex formation.

 

Hg2++2SCNHg(SCN)2Ag++2CN-[Ag(CN)2]-

 

A crucial chemical compound that combines with metals to produce complexes is EDTA.

Practice Problems

Q1. At the equivalence point, what will be relationship between the moles of acid to the moles of base in reaction mixture?

  1. They both should be equal.
  2. There are more number of moles of base.
  3. Whichever component is stronger has more moles.
  4. There are more number of moles of acid.

Solution: At equivalence point, the number of moles of acid and number of moles of base should be same in reaction mixture. Hence, they both should be equal. So, the correct answer is option (A).

Q2. On complete neutralization of 10 mL sample of 0.10 M NH3(aq) versus 0.1 M HCl (aq), there is a formation of ammonium chloride. What is the pH of the acidic salt solution at the end? (NH3(aq) ; pKb=4.74)

Solution:

As millimoles of NH3(aq) = millimoles of NH4Cl(aq) = 1millimole

(ii) Concentration of NH4Cl(aq)

 NH4Claq=1 millimole20 mL=0.05M=c

(iii) pH (salt of strong acid and weak base)

 

pH=7-12logC+pKbpH=7-12log0.05+4.74

 

pH=5.28

Q3. Titration of a 15 mL sample of 0.15 M NH3(aq) versus 0.1 M H2SO4 (aq). What is the concentration of Ammonium sulphate formed after titration?

Solution: (i) Volume of H2SO4 (aq)

          (where n is the equivalent factor)

            As millimoles of  = millimoles of  = 2.25 millimoles

 (ii) Concentration of  

Q4. Pick out the correct statement about titrand?

  1. A titrand is a solution of known concentration that is used in the titration.
  2. Any solution containing the ion or species being determined to which the titrant has been added
  3. A procedure in which a known strength solution is added to a specific volume of a treated sample containing an indicator.
  4. The point at which only enough reagent is added to completely react with a substance.

Solution: Titrand is any solution containing ions and species being determined to which titrant is added. Titrant is a solution whose concentration is already known and titration is a procedure in which a known strength solution is added to a specific volume of a treated sample containing indicator. Hence, from the given options, appropriate answer is option (B).

Frequently Asked Questions – FAQs

Q1. Why is acid base titration important?
Answer:
 The goal of a strong acid-strong base titration is to determine the concentration of an acid solution by titrating it with a known concentration of a basic solution, or vice versa, until neutralization occurs. As a result of the reaction between a strong acid-base and a strong base, water and salt are produced.

Q2. What does titration in chemistry accomplish?
Answer:
 You can find the concentration of a simple solution by titrating it with the volume of normal acid solution required to neutralize it. Finding the equivalence point, or the point at which chemically equivalent amounts of the reactants are combined, is the goal of the titration.

Q3. How does titrating a solution work?
Answer: 
Before the reaction achieves neutralization, which is sometimes indicated by a colour shift, titration is the gradual addition of a known concentration solution (referred to as a titrant) to a known volume of an unknown concentration solution.

Q4. What does titration's end point mean?
Answer:
 End point of a titration shows that the correct amount of reactant has been added to a solution to produce the desired reaction.

Q5. Why phenolphthalein is colourless in acid?
Answer:
 The acidity of phenolphthalein is low in nature. In an aqueous solution, it dissociates into and ions. The pink colour of the solution is caused by the concentration of ions within it. Under acidic conditions, the concentration of is very low, while the concentration of is very high, hence the solution is colourless.

 

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