Types of Titration: Acid-Base, Redox, Precipitation & Complexometric

Titration is a laboratory method of quantitative chemical analysis. It is used to find the unknown concentration of an analyte by the known concentration of a solution when an indicator is present. The solution that is used during titration with known accurate concentration is known as the titrant and the substance whose volume is to be found is said to be titrated. To identify the endpoint of titration for analysis, a calibrated concentration of titrant is added to an unknown concentration of analyte and when the endpoint is reached, the moles of titrant and analyte will be equal. The different types of titration are

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

Key Terms: Titration, Concentration of Solution, Acid Base Titration, Redox Titration, Precipitation Titration, Complexometric titration, volumetric analysis

---

Types of Titration

[Click Here for Sample Questions]

Titration can be classified into several types when considering goals and procedures. However, in quantitative chemical analysis, the most common types of titration are redox titration and acid-base titration.

Types of Titration

Also Read:

---

1. Acid-Base Titration

[Click Here for Sample Questions]

Acid-base titrations are when an acidic or basic titrant reacts with a base or acid analyte. It is an analytical method for determining the concentration of an acid or base by accurately neutralizing them with a known concentration standard solution of either acid or base.

HA + BOH → BA + H₂O

Acid + Alkali → Salt + Water

Or, H⁺ + A^- + B⁺ + OH^- → B⁺ + A^- + H₂O

Or, H⁺ + OH^– → H₂O

• The acid-base indicator is often known as a pH indicator, and the color indicator is used to determine the equivalent point of an acid-base reaction in titration.
• The most common pH indicators include phenolphthalein and methyl-orange.

Procedure for Acid-Base Titration

The procedure for conducting acid-base titration is as follows – 

1. Use the standard solution to rinse the burette, the unknown solution to rinse the pipette, and distilled water to rinse the conical flask.
2. Using the pipette transfer an accurately measured volume of the analyte to the flask, along with a few drops of indicator.
3. Fill the burette halfway with the standardized solution and record the volume in a worksheet.
4. We need a reasonable estimate of the amount of known solution required to neutralize the unknown solution at this point.
5. Allow the solution to drain from the burette until the indicator changes color, then note the value.
6. This is the first titration, it's not very accurate; it should be left out of any calculations.
7. Perform at least three further titrations, this time more precisely, taking into consideration the approximate endpoint.
8. At the endpoint, record the initial and final readings on the burette. (The amount of titrant used to reach the endpoint can be calculated by subtracting the initial volume from the final volume.)

9. When the indicator permanently changes color, the endpoint has been achieved.

How to Select an Acid-Base Titration Indicator?

An acid-base titration is a technique for determining if a solution contains an acid or a base.

• The acid-base indicator is usually a weak acid or weak basic in its own right, similar to the chemicals that give flowers their colour.
• A known volume of acid is placed in a conical flask during the actual procedure.
• Two to four drops of an acid-base indicator are added, and then an alkali solution of unknown strength is added drop by drop from a burette in the acid solution.
• A sharp colour change at the equivalency point denotes the neutralization point.
• Indicators range of pH between 11 to 12 may be used.
• Phenolphthalein and Methyl orange are the most often used acid-base indicators.

---

2. Complexometric Titration

[Click Here for Sample Questions]

The development of a complex between the analyte and the titrant is the basis for complexometric titrations.

• A metal-ligand complexation reaction is used in complexometric titrations.
• EDTA (Ethylenediaminetetraacetic acid) is one of the most commonly used chelating agents in analytical chemistry for complexometric titrations.

Ag⁺ + 2CN^– → [Ag(CN)₂]^–

Hg²⁺ + 2SCN^– → Hg(SCN)₂

---

3. Precipitation Titration

[Click Here for Sample Questions]

Precipitation Titration is the titration that is based on the formation of an insoluble precipitate when the two reacting substances are brought in close contact. For example, when the silver nitrate solution is used with an ammonium thiocyanate or sodium chloride solution, it reacts and forms a white precipitate of silver chloride or silver thiocyanate.

AgNO₃ + NaCl → AgCl + NaNO₃

AgNO₃  + NH₄CNS → AgCNS + NH₄NO₃

Also Read:

---

4. Redox Titration

[Click Here for Sample Questions]

An oxidation-reduction process is also known as redox titration. The chemical reaction occurs in this form of titration when electrons are transferred between reacting ions in aqueous solutions. As the reaction involved is a redox reaction, the titration between oxalic acid solution and acidified KMnO₄ solution is a redox titration. The redox indicator is the indicator used in redox titration.

Redox Titration

The concentration of the secondary standard (KMnO₄) solution is determined by titration with the primary standard (oxalic acid solution), and the concentration of the primary standard (oxalic acid solution) is determined by titration with the secondary standard (KMnO₄) solution.

KMnO₄ + H₂SO₄ → K₂SO₄ + MnSO₄ + H₂O + CO₂.

The titrations are named after the reagent that is used in are:

1. Permanganate Titrations
2. Dichromate Titrations
3. Iodometric and Iodimetric Titrations

Permanganate Titration

Potassium permanganate is used as an oxidizing agent in such titration and it is maintained with the use of dilute sulphuric acid.

• The following is the equation:

2KMnO₄ + 3H₂SO₄ → K₂SO₄ + 2MnSO₄ + 3H₂O + 5[O]

Or, MnO^–4 + 8H⁺ + 5e^– → Mn²⁺+ 4H₂O

• The solution remains colourless before the endpoint.
• The potassium permanganate is used to estimate oxalic acid, ferrous salts, hydrogen peroxide, oxalates, and so on whereas the solution of potassium permanganate is always standardized before it is used.

Dichromate Titration

Potassium dichromate is used as an oxidizing agent in an acetic medium.

• By the use of dilute sulphuric acid, the medium is maintained acidic.
• The solution of potassium dichromate can be used directly for titrations and is mainly used for the estimation of ferrous salts and iodides.

K₂Cr₂O₇ + 4H₂SO₄ → K₂SO₄ + Cr₂(SO₄)₃ + 4H₂O + 3[O]

Or, Cr₂O₂₇^- + 14H⁺ + 6e^- → 2 Cr³⁺ + 7H₂O 

Iodometric and Iodimetric Titration

Iodometric titrations are conducted when an analyte (an oxidizing agent) is added to excess iodide to produce iodine, and the amount of iodine produced is evaluated by titration with sodium thiosulfate solution.

• When a given sample of an oxidizing agent oxidizes potassium iodide in an acidic solution, an equivalent amount of iodine is freed, as in the determination of copper sulfate (CuSO₄):

2CuSO₄ + 4 KI → 2CuI↓ + I₂ + 2K₂SO₄

• Iodometric titrations are conducted when an analyte (a reducing agent) is titrated directly with a standard iodine solution.
• In iodimetry the Quantitative oxidation of reducing substances, such as arsenious acid (H₂AsO₃), can be accomplished by using common iodine solutions, as shown below:

H₃AsO₃ + H₂O + I₂ ? H₃AsO₄ + 2H⁺ + 2I^-

Gravimetric Analysis

The process of measuring the amount of an analyte by its mass is known as gravimetric analysis.

• The desired liquid constituent is transformed to a solid form that can be easily separated and weighed to ascertain its amount, and that solid mass can be used for further examination.
• In the process of preparing a solution, the desired ingredient is separated from the solution and the number of constituents is counted.
• The gravimetric analysis includes precipitation of Ag⁺, Hg₂²⁺, and Pb⁺² as halides, and precipitation of Ca²⁺ as calcium oxalate (CaC₂O₄).

Volumetric Analysis Titration

The procedure of volumetric analysis is used to calculate the amount of the desired ingredient based on its volume. As a result, it's a quantitative assessment. Titration is used to determine the volume of the ingredient (titrimetric analysis).

• A reagent that can react with the analyte is introduced in amounts to the analyte molecules until all of the analyte molecules react with the reagent molecules.
• When the sample and reagent are both colourless solutions, an indicator should be used to detect the reaction's endpoint.
• The analyte molecules reach their endpoint at the endpoint.
• When the endpoint has been reached, the indicator is a reagent that changes colour.
• When there is a change in the reaction mixture, the colour changes.
• An acid-base indicator, for example, is sensitive to changes in pH in the reaction mixture.
• When the pH is altered, the hue changes. Some reagents, on the other hand, act as self-indicators, for example, Potassium permanganate.

---

Things to Remember

• Titration is used to find the unknown concentration of an analyte by the known concentration of a solution when an indicator is present. 
• The different types of titration are Acid-base titration, Complexometric titration, Precipitation titration and Redox titration.
• The endpoint, or equivalence point, is the point at which all of the titrants have reacted.
• The titrant is a chemical whose quantity is to be found out.
• Acid-base titrations are used to determine the concentration of an acid or base sample and are carried out with the help of a burette.
• The final result of the gravimetric analysis is usually given in gram(g) in milligrams(mg), whereas the final result of the volumetric analysis is given in millilitres (mL) or in microliters.
• When the endpoint has been reached, the indicator is a reagent that changes colour.

Also Read: