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Titration

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Titration is the gradual addition of a known concentration solution (called a titrant) to a known volume of an unknown concentration solution until the reaction approaches equilibrium, which is sometimes shown by a color change. The titrant solution must satisfy the appropriate criteria to be used as a primary or secondary standard. Titration is a technique for determining the concentration of an unknown solution in a general way.

Titration Definition

Titration is a procedure that involves using a known concentration solution to determine the concentration of an unknown solution.

Titration, commonly known as titrimetry, is a chemical qualitative analytical technique for determining the concentration of an analyte in a mixture. Titration is an important technique in analytical chemistry, and it is also known as Volumetric Analysis.

Titration Formula

The formula for Titration is expressed as:

% Acid = (N × V × Equi. Weight) × 100 / (W × 1000)

where,

  • N is Normality of Titrant
  • V is Volume of Titrant
  • W is Mass of the Sample
  • Equi. Weight is Equivalent weight of acid

Titration Procedure

Titration starts with the preparation of a titrant/titrator, which is a standard solution with a predetermined volume and concentration. This titrant is then allowed to react with the analyte until an endpoint or equivalence point is reached, at which point the analyte concentration can be estimated by measuring the amount of titrant consumed. Titration, on the other hand, is a stoichiometric technique used to determine a solution’s unknown concentration.

In terms of method steps, a highly exact amount of analyte is introduced to a beaker or Erlenmeyer flask. A little amount of the titrant (such as phenolphthalein) is placed beneath a calibrated burette or chemical pipetting syringe containing the indicator.

Small amounts of titrant are mixed into the analyte and indicator. This will continue until the indicator’s color changes in response to the titrant saturation threshold. At this moment, it will show that we have reached the end of the titration. Essentially, the amount of titrant present during the reaction balances the amount of analyte present.

Techniques for Preparation

Both the titrant and the analyte must be in liquid (solution) form. To dissolve the solids, solvents such as glacial acetic acid or ethanol are utilized. To improve accuracy, concentrated analytes are additionally diluted. A steady pH is required or should be maintained during the reaction in the majority of non-acid–base titrations. To maintain the pH, a buffer solution is introduced to the titration chamber.

For particular conditions in the reaction chamber, a separate masking solution is occasionally introduced to eliminate the influence of the undesired ion. To accelerate the pace of some redox reactions, the sample solution must be heated and titrated while still hot.

Chemical Analysis

Chemical Analysis means finding out the chemical species present in the compound as well as its quantity in the compound. Based on this Chemical Analysis is of two types:

  • Qualitative Analysis: It involves the identification of various chemical species present in a compound.
  • Quantitative Analysis: It involves the measurement of quantities of chemical species present in a compound.

Titration is a Quantitative Analysis of Chemicals performed to calculate the concentration of a chemical species present in the solution. The endpoint of titration can be measured by the following methods:

  • Gravimetric Analysis
  • Volumetric Analysis
  • Spectroscopy
  • Combustion

The process of finding unknown concentration involves the use of the mole concept hence one must have good knowledge of the mole concept for balanced chemical equations and equivalence concepts for unbalanced chemical equivalence.

Types of Titration

Titration is classified on two bases namely, the Types of Reactions Involved and the Number of Components in the Titrate.

Based On the Reactions Involved there are the following types

  • Acid-Base Titration
  • Redox Titration
  • Precipitation Titration
  • Complexometric Titration

Based on the Number of Components in the Titrate there are the following types

  • Single Titration
  • Double Titration

Let’s first study the types of titration on the basis of the types of reactions involved:

Acid-Base Titration

Acid-Base titration aims to find out the strength of an acid or base of unknown concentration using a base titrant for acid and an acid titrant for a base. Acidimetry is the measurement of acid strength using a standard solution of the base. Similarly, alkalimetry can be used to determine the strength of a base using a standard solution of an acid.

This titration is based on the principle of Neutralization Reaction. We know that when acid and base react, Neutralization Reactions occur.  We try to find how much titrant of known concentration is used to Neutralize the acidic or basic solution of unknown concentration present. In an acid-base titration, one solution is an acid and the other is a base. Furthermore, one is placed in a flask, while the other is placed in a burette and dripped into the flask until the titration reaches its endpoint. For Example: 

HA + BOH  →  BA + H2O

where,

  • HA is acid and A is a negative ion
  • BOH is base and B positive ion

This titration is based on the neutralizing reaction between a base or an acidic and an analyte. In addition, a reagent is combined with the sample solution until it reaches the desired pH level. This type of titration is heavily reliant on the pH track or a pH meter.

Procedure for Acid-Base Titration

One should perform the Acid-Base Titration by following the below-mentioned steps:

  • Step 1: Prepare the titrant of known concentration, acid titrant for a base solution, and base titrant for an acid solution.
  • Step 2: Using Pipette measure the prepared titrant and pour it into a conical flask.
  • Step 3: Add a few drops of an indicator to the flask.
  • Step 4: Prepare a solution of the acid or base which is to be titrated and fill it in a burette.
  • Step 5: Fix the burette in a stand clamp and add the solution of unknown concentration drop by drop into the conical flask which has the titrant.
  • Step 6: When the reaction occurs, the color of the solution in the flask changes due to the presence of an indicator.
  • Step 7: At this point note down the change in volume of solution from burette.
  • Step 8: Perform the titration three times for accuracy.
  • Step 9: After three times of titrations, do the necessary calculation with errors taken into account.

Selection of Indicator for Acid-Base Titration

The acid and base are of two types namely strong and weak depending upon the ability to dissociate ions. It is easy to achieve the endpoint in the case of strong acid and strong base but difficult in the case of weak acid and weak base. 

In case, we have to titrate a solution of weak acid of unknown concentration then we will use a strong base of known concentration as titrant because the conjugate of a weak acid is a strong base.

If we have to titrate a solution of a weak base of unknown concentration then we will use a strong acid of known concentration as titrant because the conjugate of a weak acid is a strong acid.

Here in both scenarios, methyl orange is added as an indicator which is orange in the acidic solution and yellow in the basic solution.

Methyl orange Titration

 

 Another indicator used is Phenophthalien which is colorless in acidic solution and pink in basic solution.

Phenophthalien Titration

 

Redox Titration

As the name suggests this Titration is an example of an oxidation-reduction reaction. The chemical reaction in this titration occurs through the transfer of electrons in the reactive ions of aqueous solutions. One solution in redox titration is a reducing agent, while the other is an oxidizing agent. In this, we aim to find out the concentration of the reducing or oxidizing agent. We generally prefer the equivalence concept as balancing a redox reaction is a hectic task. Redox titration is further classified on the basis of the reagent used. They are mentioned below:

  • Permanganate Titration
  • Dichromate Titration
  • Iodimetric and Iodometric Titration

Permanganate Titration

Potassium permanganate is used as an oxidizing agent. It is kept in good condition by using dilute sulphuric acid.

MnO4– + 8H + 5e → Mn2++ 4H2O

Before the endpoint, this solution is colorless. Furthermore, potassium permanganate is used to calculate oxalic acid, ferrous salts, hydrogen peroxide, oxalates, and many other substances.

Dichromate Titration

In an acidic medium, potassium dichromate is undoubtedly used as an oxidizing agent. Furthermore, the acidic medium is maintained by the use of dilute sulphuric acid.

K2Cr2O7 + H2SO4 → K2Cr2SO4 + H2O + 6O

Iodimetric and Iodometric Titrations  

In this titration, we use iodine or iodine solution as a titrant. Iodine is used in two ways in these titrations:

Iodimetric Titration

In the case of Iodimetric Titration, the I2 molecule is used as a titrant against a solution of a reducing agent which is of unknown concentration. In this I2 is converted to iodide ion. The reaction is mentioned below.

l2 + 2e → 2l–                                …….. (reduction)

Iodometric Titration

In the case of Iodometric Titration, the I the molecule is used as a titrant against a solution of an oxidizing agent which is of unknown concentration. In this, I is converted to an Iodine molecule. The reaction is mentioned below.

2l– → I2 + 2e                      ……. (oxidation)

Precipitation Titration

This titration is based on precipitate production. In precipitation titration, we put two reacting chemicals into contact. For example: When silver nitrate solution is used, ammonium thiocyanate or sodium chloride solution is used. When it interacts, it produces a white precipitate of silver thiocyanate or silver chloride.

AgNO3 + NaCl → AgCl + NaNO3

This titration is often followed by Gravimetric Analysis Titration to calculate the concentration of ion present in the precipitate.

Gravimetric Analysis Titration

Gravimetric Analysis is a quantitative tool to measure the mass concentration of ion present in the precipitate. It involves the following steps:

  • Step 1: After the reaction achieves the equivalence point, the precipitate is formed and this precipitate is collected as the sample.
  • Step 2: The sample so collected is then dried and crushed into powder.
  • Step 3: At this stage, Gravimetric Analysis is done by measuring the mass of the sample and finding out the percentage of ion present.

As we have talked about Equivalence Point in the above steps let’s learn about Endpoint and Equivalence Point.

Equivalence Point & Endpoint

Equivalence point is the point where titrant and analyte become chemically equivalent in terms of quantities. This doesn’t mean to become equal quantity. This means the stoichiometric ratio of titrant and analyte would be such that there is a complete reaction as per the stoichiometric balanced equation.

Endpoint is the point where the color change is observed after the reaction has happened. It is related to Equivalence Point but not the same. It comes after Equivalence Point.

Complexometric Titration

The development of an undissociated compound occurs most importantly in this titration. It is also more than only precipitation titrations. For Example: 

Hg2+ + 2SCN– → Hg(SCN)2

EDTA, or ethylenediaminetetraacetic acid, is an essential reagent that produces compounds with metals.

Volumetric Analysis Titration

Volumetric Analysis involves the calculation of the unknown concentration of an analyte when titrated against a standard solution of a titrant with a known concentration. In this case, the volume of the titrant and analyte both are known. There are some pre-requisite conditions for Volumetric Analysis which are mentioned below:

  • The reaction should be of moderate rate means neither too fast nor too slow
  • The equation for the reaction must be known.
  • Endpoint for the reaction must be detectable.
  • Any side reaction should not be there which interferes with the main reaction.

There are two basic components of a Titration

  • Titrant: The solution whose concentration is known.
  • Analyte: The solution whose concentration is unknown.

Standard Solution: The titrant is prepared from a solution of known concentration. This is called a standard solution. It is of two types, Primary and Secondary.

  • Primary Standard Solution: This is prepared by dissolving a calculated quantity of solute in a known volume of solvent. It is highly pure.
  • Secondary Standard Solution: This is prepared by comparing against the primary standard solution because in their original form they are not stable.

The characteristics of standard solution are

  • Should be Pure
  • Should be Stable
  • High Molecular Mass
  • There should be no change in its concentration with time.

Volumetric Analysis Titration is of three types Simple Titration, Back Titration, and Double Titration. Simple Titration consists of Acid-Base Titration, Redox Titration, Precipitate Titration, and Complexometric Titration. All these we have studied above. Let’s study Back Titration and Double Titration.

Back Titration

Back Titration is the type of titration in which the unknown concentration of analyte is found out by reacting the analyte with a known amount of extra reagent and the remaining reagent is titrated against the second reagent. It is used when the reaction is too slow or in case of weak acid or base when it becomes difficult to find out the Endpoint.

Double Titration

As the name suggests, in Double Titration two different solution of known concentration is used to find the unknown concentration of the sample. It is an Indirect Titration method that is used to find the concentration of analyte in Acid-Base titration. In this first titration is done to standardize a reagent using another reagent. Now this standardized reagent is used to find the concentration of the sample.

Besides the above mentioned there are some more types of titration mentioned below.

Gas Phase Titration

In Gas Phase Titration, the reactants are in the gas phase. It is based on the principle of Beer-Lambert’s law which states that the concentration of a solution is directly proportional to the absorption of light by it.

Zeta Potential Titration

Zeta Potential Titration is used for heterogeneous systems such as colloidal and suspension etc. In this, the charge carried by the particles of colloidal and suspension is measured and used for finding the concentration of the sample. The measurement of charge is called Zeta Potential.

Assay

Assay refers to the purity of the substance in titration. It helps in determining the concentration of the solution because the more concentrated solution the more accurate will be the titration. The purity can be measured by gravimetric or volumetric analysis.

Titration Curve

Titration Curve is a graph between the pH of the analyte and the volume of the titrant. The equivalence Point from the curve is given by the point of inflection.

Titration Curve

 

Read More,

FAQs on Titration

Q1: What is Titration?

Answer: 

Titration, commonly known as titrimetry, is a chemical qualitative analytical technique for determining the concentration of an analyte in a mixture.

Q2: What is the difference between Equivalence Point and End Point?

Answer: 

Equivalence Point is the point where titrant and analyte become chemically equivalent as per stoichiometry of the reaction while End Point is the point where color change happen in the titration?

Q3: What do you mean by Redox Titration?

Answer:

The chemical reaction in which titration occurs through the transfer of electrons in the reactive ions of aqueous solutions. One solution in redox titration is a reducing agent, while the other is an oxidizing agent.

MnO4– + 8H + 5e → Mn2++ 4H2O

Q4: What is the difference between Iodimetric and Iodometric titration?

Answer:

Iodimetric titration involes use I2 as titrant which get reduced to I when used for titration against a reducing agent while Iodometric involves use of I which get oxidized to I2 when used to titrate an oxidizing agent.

Q5: What is Titration Curve?

Answer: 

Titration Curve is a plot of graph between pH of Analyte vs Volume of the titrant added. The inflection point represents the Eqivalence Point of the reaction.



Last Updated : 19 Dec, 2023
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