Simple Titration - Definitions, Examples, Practice Problems & FAQs

If you have an unknown solution, how can you find the normality of an unknown solution?

The normality of an unknown solution is calculated by titration against a known standard solution. Take unknown solution in a conical flask and standard solution in a burette and add drop by drop to a conical flask. The endpoint of the process is indicated by a suitable indicator.

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Table of contents:

Titration
Standard solution
Equivalence point
Indicators
Acid-base titration
Redox titration
Practice problems
Frequently asked questions-FAQs

Titration

Titration is the steady addition of a known concentration solution (known as a titrant) to a known volume of an unknown concentration solution (known as the analyte) until the reaction reaches the end point, which is often indicated by a change of colour.

Standard solution

It is defined as a solution whose concentration is known. Generally, it is taken in a burette.

Type of standard solution:

Primary standard solution
Secondary standard solution

Primary standard solution:

The reagents that can be accurately weighed and their solution need not be standardized before use as these reagents do not react with air or moisture.

Examples: Oxalic acid (H2C2O4), Potassium dichromate (K2Cr2O7), Silver nitrate (AgNO3), Copper sulfate (CuSO4), ferrous ammonium sulfate (Mohr’s salt), Hypo solutions (Na2S2O3), etc.

Secondary standard solution:

The reagents that cannot be accurately weighed and their solution needs to be standardized before use as these reagents can easily react with air or moisture.

Examples: Sodium hydroxide (NaOH), Potassium hydroxide (KOH), Hydrochloric acid(HCl), Sulphuric acid (H2SO4), I2 solution, Potassium permanganate (KMnO4), etc.

Equivalence point

Number of equivalents of the titre = $\frac{n u m b e r o f e q u i v a l e n t o f s o l u t e}{v o l u m e o f s o l u t i o n (L)}$

Analyte: It is the solution with an unknown concentration.

The titrant is the solution with a known concentration (standard solution).

The normality of a solution can be calculated as:number of equivalent of solutevolume of solution (L)

Number of equivalent = $M o l e \times n - f a c t o r = N o r m a l i t y \times V o l u m e (L)$

At the equivalence point,

Number of the equivalent of analyte = number of the equivalent of titrant

$\Rightarrow N_{t i t r e} V_{t i t r e} = N_{t i t r a n t} V_{t i t r a n t}$

Endpoint

The endpoint is defined as the point during titration at which the indicator changes its colour.

Types of titration:

Acid-base titration
Redox titration

Indicators:

Indicators are generally organic weak acids or weak bases which show different colours in ionized and unionized forms or different colours in different pH ranges.

E.g-, Phenolphthalein is an organic weak acid (phenolphthalein ionized form is pink coloured and unionized form is colourless)

Methyl orange (MeOH) is a weak organic base (the ionized form is red and the unionized form is yellow).

List of some indicators and their colour according to pH

Indicator	pH Range	Acid	Base
Phenolphthalein	8.0-10.0	colourless	pink
Thymol Blue	1.2-2.8	red	yellow
Tetrabromphenol blue	3.0-4.6	yellow	blue
Methyl red	4.4-6.2	red	yellow
Rosolic acid	6.8-8.0	yellow	red
Thymolphthalein	9.4-10.6	colourless	blue
Tropeolin O	11.0-13.0	yellow	orange-brown

Generally, in acid-base titration phenolphthalein and methyl orange used as indicators.

Acid-base titration

It is the method of finding the concentration of an unknown acid/base by titrating it against a base/acid with a known concentration.

Redox titration

In redox titration, the oxidizing agent (O.A.) reacts with the reducing agent (R.A.) to give products. In redox titrations, electrons are transferred between the titre and the titrant.

$O . A . + R . A . ⟶ P r o d u c t s$

At the equivalence point,

Equivalent of oxidizing agent = equivalent of reducing agent

Practice problems:

Q 1. Phenolphthalein changes colour in presence of

a. NaOH
b. NaCl
c. NaHCO₃
d. HCl

Answer: (C)

Solution: Phenolphthalein changes colour in presence of NaHCO₃, weakly basic medium. Phenolphthalein changes colour in pH range 8.0 to 10.0 (colourless to pink).

Q 2. Methyl orange changes colour in presence of

a. NaOH
b. H₂CO₃
c. NaHCO₃
d. HCl

Answer: (B)

Solution: Methyl orange changes colour in presence of H₂CO₃, weakly acidic medium. Methyl orange changes colour in the pH range from 3.1 to 4.4 (red to yellow).

Q 3. What is the normality of a solution of sulphuric acid, 15 mL of solution neutralizes 20 mL of 0.2 N NaOH solution?

a. 0.1 N
b. 0.267 N
c. 0.54 N
d. None of these

Answer: (B)

Normality of NaOH= 0.2 N

Volume of $N a O H = 20 m L = \frac{20}{1000} L$

Volume of $H_{2} {S O}_{4} = 15 m L = \frac{15}{1000} L$

At the equivalence point,

Number of the equivalent of H2SO4 = number of the equivalent of NaOH

$\Rightarrow N_{H_{2} {S O}_{4}} \times V_{H_{2} {S O}_{4}} = N_{N a O H} \times V_{N a O H}$

$\Rightarrow N_{H_{2} {S O}_{4}} \times \frac{15}{1000} = 0.2 \times \frac{20}{1000}$

$N_{H_{2} {S O}_{4}} = 0.267 N$

Q 4. Solution of 20 mL of 0.2 M ferrous sulfate titrated with potassium permanganate in an acidic medium. Calculate the total amount of potassium permanganate used

a. 10 mL of 0.2 M
b. 10 mL of 0.3 M
c. 20 mL of 0.2 M
d. 1 mL of 0.8 M

Answer: (D)

In acidic medium, $F e {S O}_{4} (s) + K M {n O}_{4} (a q) \to F e^{3 +} (a q) + M n^{2 +} (a q)$

Element	Initial oxidation state	Final oxidation state
Fe	+2	+3
Mn	+7	+2

Molarity of FeSO4= 0.2 M

Volume of FeSO4= 20 mL

$n - f a c t o r o f K M {n O}_{4} = 1 \times | 7 - 2 | = 5$

$n - f a c t o r o f F e {S O}_{4} = 1 \times | 3 - 2 | = 1$

At the equivalence point,

Number of the equivalent of KMnO4 = number of the equivalent of FeSO4

$\Rightarrow N_{K M {n O}_{4}} \times V_{K M {n O}_{4}} = N_{F e {S O}_{4}} \times V_{F e {S O}_{4}}$

$\Rightarrow {5 \times M}_{K M {n O}_{4}} \times V_{K M {n O}_{4}} = {1 \times 0.2}_{\times} 20$

${\Rightarrow M}_{K M {n O}_{4}} \times V_{K M {n O}_{4}} = 0.8$

Frequently asked questions-FAQs

Q. What is the difference between endpoint and equivalence point titration?
Answer: The endpoint mode simulates the traditional titration technique, in which the titrant is added until the reaction is completed, as shown by a colour change in an indicator. The sample is titrated with an automatic titrator until a predetermined value is obtained.

The equivalency point is defined as the point where the analyte and reagent are present in equal amounts. In most circumstances, it's almost identical to the titration curve's inflexion point, such as titration curves generated from acid/base titrations. The associated pH or potential (mV) value and titrant consumption establish the curve's inflexion point (mL). The equivalency point is determined by the intake of a known concentration of titrant. The amount of substance that has reacted with the sample is calculated as the product of titrant concentration and titrant consumption. The measured points in an autotitrator are evaluated using certain mathematical processes, resulting in an evaluated titration curve. This evaluated curve is then used to calculate the equivalence point.

Q. In which industries or segments is titration used?
Answer: Titration is an extremely valuable analytical tool to check, primarily the purity of samples. This method has its used in a variety of fields such as electronics, Electroplating, Energy, Explosives, Machinery, Coal products, Coating, Textile, Food & Beverage, Paper&Pulp, and Petroleum, to name a few.

Q. Define titration curve.
Answer: The titration curve is plotted between pH of solution vs volume of titrant added, with the help of obtained curve we can decide which indicator is suitable for alarming the completion of the titration process.

Q. What are the different types of titrations?
Answer: The following is a list of several types of titrations such as

1. Titration of acid and base
2. Titration using complexometry
3. Redox Titration
4. Titration using iodine is called iodometry and iodimetry
5. Titration through precipitation
6. Titration using permanganate ion