What is Titration?
Titration is a method commonly used in laboratories for the quantitative estimation of an analyte i.e., using the method of titration the concentration or strength of a given chemical is determined.
Titration is basically used in volumetric analysis. Volumetric analysis can be used for many types of estimation and various types of titrations can be classified under the following categories:
Acid-base titration
Redox titration
Precipitation titration
Complexometric titration
Titration chemistry: In general, we can state that titration is a mode of quantitative analysis involving the estimation of the quantity of a chemical species by measuring the volume of the solution of that particular species in a suitable solvent. This method is based on the Law of Equivalence. So, it can be said that titration is the process of determining the volume of the reagents by bringing about a definite reaction to just completion.
The solution used during titration whose accurate concentration is known is called titrant and the substance whose volume is to be determined is said to be titrated.
Acid-Base Titration
The determination of the strength of a solution of acid by titrating it with a standard solution of a base, or the determination of the strength of a solution of alkali by the means of titration with a standard solution of acid, is termed as acid-base titration.
Titration chemistry in detail
The completion of the reaction between an acid and an alkali is termed neutralization and it proceeds with the formation of salt and water according to the general equation:
Acid + Base 🡪 Salt + Water
The detection of the endpoint of the titration is assisted by the addition of an indicator to the system under investigation. The indicator employed in these titrations is required to indicate the equivalent point rather than the true neutral point. At the point of equivalence, the pH of the solution could be equal to, greater than or less than 7, depending on the relative strengths of the acid and alkali. The salt formed by the solution at the end of the reaction may suffer hydrolysis to some extent and the pH of the solution will either be less than or more than 7. The solution is, thus, not truly neutral.
Indicators are used during acid-base titration. The indicators employed are either weak organic acids or weak organic bases. Their degree of dissociation is greatly affected by any alteration in the hydrogen ion concentration of the solution. An acid indicator can be expressed by the general formula HIn and the basic indicators as InOH.
The dissociated and undissociated forms a dynamic equilibrium mixture of two tautomeric forms having different structural formulae and colours. One of these exists in an acidic medium, while the other in an alkaline medium. The change in pH causes the transformation from one form to the other and vice-versa; and consequently, a change in colour is seen.
Two such indicators are: Phenolphthalein, Methyl orange
pH range of some common acid-base indicators
Usually, an indicator such as phenolphthalein is used for the titrations involving a strong alkali and an indicator like methyl orange is used for titrations involving a strong acid.
What is Acid-Base Titration?
In order to do the titration, 100ml of the acid/base, that is to be titrated, is taken in a conical flask and a drop of phenolphthalein is added. Suppose, we take the acid in the flask. The counter chemical i.e. the base is taken in the burette and the titration is done until a sharp change in the colour is observed. Phenolphthalein gives pink colour in basic medium. When the sharp change in colour is seen, the addition of the base is stopped and the amount of base added is noted down. By using the concept of normality, and the law of equivalence, and using the known value of the concentration of the base, the unknown concentration of the analyte i.e., the acid that was titrated is determined.
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The basic concept of acid base titration is based on this neutralization curve. The calculations for the determination of the strength or concentration of the unknown analyte are done using the law of equivalence.
Law of equivalence:
For a neutralization reaction, the number of equivalents of an acid must be equal to the number of equivalents of the base at the end point / equivalence point.
Normality X Volume = Number of equivalents
Normality = No. of equivalents of the solute dissolved in 1L of the solution.
No. of equivalents for an acid can be calculated as (Molecular weight) / Basicity.
No. of equivalents for an acid can be determined as (Molecular weight) / Acidity.
The overall titration chemistry lays its foundation on this law of equivalence only.
In general, during titration, an indicator showing change in color is taken. However, in potentiometric titrations, change in pH is taken for the acid base titration and in such titrations, there’s no requirement for the addition of an indicator because the end point is analyzed by the change in the pH of the solution.
Conclusion
This was all about acid base titration where an acid and a base were involved, of which the concentration of one was known and the concentration of the other was unknown; the titrations are performed in order to determine the concentration of the unknown using the known solution.
FAQs on Types of Titration - Acid Base Titration
1. What are redox titrations and what are their types?
The redox titrations are an oxidation-reduction reaction wherein, the transfer of electrons in the reacting ions causes a chemical reaction to occur in the aqueous solution. There are three different types of redox reactions that are named on the basis of the reagent used. The types of redox reactions are namely, permanganate titrations, dichromate titrations, and iodometric titrations.
Permanganate titrations make use of potassium permanganate as an oxidizing agent along with the use of dilute sulphuric acid. This titration is used for estimating the presence of oxalic acid, oxalates, hydrogen peroxide, and ferrous salts. The solution containing potassium permanganate remains colourless before the endpoint.
Dichromate titrations make use of potassium dichromate as an oxidizing agent in the acidic medium by the use of dilute sulphuric acid. The potassium dichromate titration is applied for the prediction of the presence of iodides and ferrous salts.
The iodometric and iodometric titrations involve the reduction of free iodine to iodide ions and also the oxidation of iodide ions to free iodine which is used for the iodometric titration.
2. What is the difference between complexometric titrations and redox titrations?
Complexometric titrations refer to a type of titrations where a coloured complex is formed that helps in determining the endpoint of titration while redox reactions are a type of titration that involves the use of an oxidizing agent and a reducing agent. In a complexometric titration, the complexion is formed from simple ions whereas, in redox reactions, the complete oxidation or reduction of the components takes place.
Complexometric titration produces a colour change as the indicator of endpoint while redox reactions cause a change in the potential to detect the endpoint. Complexometric titrations are applied for estimation of the amount of hardness in water, for determining the metal concentration of drugs in the pharmaceutical industry, and for determining the content of titanium dioxide in cosmetic products. Redox titrations are used for analyzing pharmaceutical products and cosmetic products.
3. How do we determine the endpoint of titration?
At the point of equivalence of titration, the equivalent point of titrant is added to the sample. The endpoint refers to the moment during an experiment at which the reaction is identified as complete due to a signal produced in the solution. These signals produced in a titration test are generally in the form of changes in the colour of an indicator or changes in the electric properties caused during the titration.
The difference between the endpoint and the equivalence point is known as the titration error. The value of titration error can be reduced by choosing a suitable end-point signal and ways of detecting it. The indicator in an experimental procedure must be chosen wisely taking the nature of the titration procedure into consideration. The procedure of titration completes when the colour of the indicator changes. The endpoint of a titration process is used to calculate the concentration of the analyte with reference to a known concentration of the titrant.
4. How can I perform acid-base titration?
An acid-base titration is one of the simplest and most basic practicals conducted in a laboratory. The main steps for performing an acid-base titration are
Rinse the pipette, burette, and conical flask with a standard solution and distilled water.
Transfer a precisely measured volume of the analyte through a pipette into an Erlenmeyer flask and add a few drops of indicator to the flask containing the analyte.
Now, fill the burette with a standard solution and note the volume of the solution present in the burette.
Now, let the solution from the burette drain into the flask containing the analyte until the colour of the analyte changes.
Stop the burette when the colour of the analyte changes and do not disappear on shaking the flask, note the reading of the burette at this point.
Now, repeat the step three more times and note down the initial and final reading of the burette after each turn.
The amount of titrant used can be calculated by subtracting the initial volume of the solution in the burette to the final volume of the solution left in the burette.
5. How can I select an appropriate indicator for acid-base titration?
An acid-base titration is an experimental technique to predict if a solution is an acid or a base. The indicators used for detecting if a solution is an acid or a base are generally weak acids or weak bases. Methyl orange is the most commonly used indicator for bases whereas phenolphthalein is the most common indicator used for the prediction of acids. In acid-base titrations, a known volume of acid is kept in a conical flask along with a few drops of any acid-base indicator. The alkali solution of unknown strength is poured into the flask drop by drop using a burette. A sharp change in the colour of the solution indicates the neutralization point, that is, the equivalence point.
