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Titration

Titration:

-The process of determining strength or concentration of unknown solution by the help of standard solution in presence or absence of indicator.

Types of Titration:

1) Redox titration:

-Strength of oxidizing agent is determined by standard reducing agent or vice versa.

-Example:

$2 K M n^{+ 7} O_{4} (p ink) + 5 H_{2} C_{2}^{+ 3} O_{4} + 3 H_{2} S O_{4} ⟶ K_{2} S O_{4} (co l or l ess) + 2 M n^{+ 2} S O_{4} + 10 C^{+ 4} O_{2} + 8 H_{2} O$

Here,

$K M n O_{4}$ is oxidizing agent and $H_{2} C_{2} O_{4}$ is reducing agent.

$K M n O_{4}$ is self-indicator.

2) Acid-Base Titration:

-Concentration of an acid is determined by standard alkali or vice versa.

$N a O H (a q .) + H Cl (a q .) ⟶ N a Cl (a q .) + H_{2} O$

-An acid – base titration is usually of four types and each sets definite criteria for selection of indicators.

i) Titration involving strong acid and strong base:

-In this type of reaction, there is a sharp change in pH around neutralization point.

-The pH of this point varies from $3.3 t o 10.7$ .

-Thus, a indicator of range $3-10.5$ can be used.

- Both phenolphthalein and Methyl orange can be used.

ii) Titration involving strong acid and weak base:

-In this type of titration the equivalent point lies on the pH range of $3.5 t o 7.0$ .

-Acidic indicator can be used like Methyl orange.

iii) Titration involving strong base and weak acid:

-The titration has equivalent point in the pH range of $7.7 t o 9.7$ .

-Basic indicator like phenolphthalein may be used.

iv) Titration involving weak acids and weak base:

-There is no sharp change in pH, accurate measurement of end point in this case is not shown by indicators.

3) Precipitation Titration:

-Those titration in which precipitate is formed as a result of reaction between the reacting solution.

$N a Cl (a q .) + A g N O_{3} (a q .) ⟶ A g Cl ↓ + N a N O_{3} (a q .)$

4) Iodometric and Iodimetric Titration:

Iodimetric Titration:

-Those titration in which standard iodine solution is used for titration.

$2 N a_{2} S_{2} O_{3} + I_{2} ⟶ N a_{2} S_{2} O_{6} + 2 N a I$

Iodometric titration:

-Those titration in which the liberated iodine from $K I$ is titrated with sodium thiosulphate solution are called iodometric titration.

-Example:

$2 C u S O_{4} + 4 K I ⟶ 2 K_{2} S O_{4} + C u_{2} I_{2} + I_{2}$

$2 N a_{2} S_{2} O_{3} + I_{2} ⟶ 2 N a I + N a_{2} S_{4} O_{6}$

Terms Used in Titration:

Titrant:

-The solution of known concentration used in a titration which is generally taken in burette.

Titrand:

-The solution of unknown concentration used in titration which is generally taken in titration flask by using pipette.

Alkalimetry:

-The process of determining the strength of acid by titrating with standard solution of alkaline solution.

Acidimetry:

-The process of determining the strength of base by titrating with standard solution of alkali solution.

End Point:

-The point at which reaction completes as indicated by change in colour of indicator.

-It is the practical point.

Equivalence Point:

-The point at which equivalent amount of titrant is neutralized by the titrand.

-Theoretical end is known as equivalence point.

Titration Error:

-The difference between end point and equivalence point.

Indicator:

-The chemical substance which indicates the completion of reaction by changing it's colour.

-Example: phenolphthalein, methyl orange, litmus paper, methyl red, etc.

Normality factor:

Ratio of practical weight to theoretical weight.