Principles Related to Practical Chemistry  

What is Principles Related to Practical Chemistry

This chapter is all about the study of various methods and techniques that help to determine the amount of any particular element present in a given compound. In this chapter, analysis is divided into three categories i.e, inorganic, organic and physical. There are various tests available that we perform to determine an element in the compound.

There are various real-life applications that we see in our daily life around us. Some of them are mentioned below:

  • The estimation of nitrogen is done using two different methods i.e, Duma's method and Kjeldahl's method.


Principles Related to Practical Chemistry    Principles Related to Practical Chemistry
                               Duma's method                                                                         Kjeldahl's method                       

  • For quantitative estimation of halogens, the carius method is used. The pictorial representation of the process is given below.
    Principles Related to Practical Chemistry examples

 

Notes for Principles Related to Practical Chemistry

In this section, you will study about the important topics of the chapter, overview, formulae and some important tips and guidelines for the preparation of the chapter at the best.

Important Topics

  • Qualitative analysis for inorganic salts
  • Preliminary tests
  • Flame tests
  • Wet Tests
  • Detection of nitrogen
  • Detection of Sulphur
  • Detection of Halogens
  • Volumetric analysis

 

Overview of the Principles Related to Practical Chemistry

In this chapter, we study the various methods and processes for the determination of various elements qualitatively and quantitatively. All these methods are divided on the basis of nature of compounds i.e, inorganic, organic and physical. These processes are discussed below.

 

Inorganic Chemistry

Qualitative Analysis

The qualitative analysis deals with the identification of various constituents present in a given compound. It focuses on detecting ions in aqueous solution. It is a branch of analytical chemistry which determines the elemental composition in various compounds. This analysis involves preliminary tests, flame test and wet tests for anions and cations, etc.

  • Preliminary Tests
    The preliminary tests of inorganic salts involve the study of colour, odour and heating as mentioned below.
    (i) Colour: Mg2+(white), Cu2+(blue), Fe3+(brown), Co2+(pink), etc.
    (ii) Odour: NH4+(ammoniacal smell), CH3COO-(vinegar smell), S2-(smell of rotten eggs).
    (iii) Heating: Several changes observed when inorganic salts are heated. Some salts when heated changes their colour. For example, CuSO4.5H2O changes from blue to white. Some inorganic salts produced sound, for example, when NaCl is heated, then the crackling sound is produced

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  • Flame Tests
    Flame tests are done to identify the possible metal atom or ion present in the compound. In this test, a sample is placed on the flame of the burner, then the corresponding colour or sound helps to identify the element. For example, when a salt with few drops of HCl is paced on the flame with the help of a metal wire, then the colour of the flame determines the metal ion. In this experiment, if the colour of the flame is apple green then it is the presence of Ba+. Similarly, if the flame colour is golden yellow then it is due to Na+.

 

  • Wet Tests
    Wet tests are those which are performed by dissolving the salts in water, acid or base. Wet tests are done to identify either the acidic radicals or basic radicals.
    (i) Group I acidic radicals: This test is done when a salt is dissolved with dilute HCl or dilute H2SO4. Thus the evolution of gases indicates the presence of group I acidic radicals. Some examples include:
    (a) In this case, Na2CO3 is dissolved with dilute H2SO4 and the evolved CO2 indicates the presence of carbonate ion.
        \mathrm{Na}_{2} \mathrm{CO}_{3}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}+\mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2} \uparrow
    (b) In this case, Na2SO4 is dissolved with dilute H2SO4 and the evolved SO2 indicates the presence of sulphite ion.
        \mathrm{Na}_{2} \mathrm{SO}_{3}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}+\mathrm{H}_{2} \mathrm{O}+\mathrm{SO}_{2} \uparrow

    (ii) Group II acidic radicals: This test is done when a salt is dissolved with concentrated HCl or concentrated H2SO4. Thus the evolution of gases indicates the presence of group II acidic radicals. Some examples include:
    (a) In this case, NaCl is dissolved with concentrated H2SO4 and the evolution of HCl gas indicates the presence of chloride ions.
         \mathrm{NaCl}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{NaHSO}_{4}+\mathrm{HCl}\uparrow
    (b) In this case, NaBr is dissolved with concentrated H2SO4 and the evolution of Br2 gas indicates the presence of bromide ions.
         \\\mathrm{NaBr}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{NaHSO}_{4}+\mathrm{HBr}\\ 2 \mathrm{HBr}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{Br}_{2} \uparrow+2 \mathrm{H}_{2} \mathrm{O}+\mathrm{SO}_{2}

    (iii) Group III acidic radicals: These radicals are not detected by dilute acid or concentrated acid. These radicals require special tests for identification. Some examples include:
    (a) In this case, Na2SO4 is reacted with BaCl2 and forms white precipitation of BaSO4. The reaction occurs as follows:
         \mathrm{Na}_{2} \mathrm{SO}_{4}+\mathrm{BaCl}_{2} \longrightarrow \mathrm{BaSO}_{4} \downarrow+2 \mathrm{NaCl}
    (b) In this case, Na3BO3 is reacted with H2SO4 and after subsequent reactions finally, ethyl borate is formed which gives green flame on burning. The reactions occur as follows:
         2 \mathrm{Na}_{3} \mathrm{BO}_{3}+3 \mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow 3 \mathrm{Na}_{2} \mathrm{SO}_{4}+2 \mathrm{H}_{3} \mathrm{BO}_{3}
         \mathrm{H}_{3} \mathrm{BO}_{3}+3 \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH} \longrightarrow\left(\mathrm{C}_{2} \mathrm{H}_{5}\right)_{3} \mathrm{BO}_{3} \uparrow+3 \mathrm{H}_{2} \mathrm{O}

    (iv) Basic radicals: Transparent solutions are made by dissolving salts in a suitable solvent. Usually, the salts are dissolved in distilled water. Once this solution is prepared then it shows the presence of basic radicals as mentioned below:
    (a) If the solution is coloured then it is the presence of transition metal ions.
    (b) If a solution is prepared in HCl and white precipitation is formed then it is the presence of Pb2+.
    (c) If a solution is prepared in water and the colour changes from pink to blue then it shows the presence of Co2+.

 

Organic Chemistry

Qualitative analysis
In addition to carbon and hydrogen, organic compounds may also contain oxygen, nitrogen, sulphur, halogens and phosphorus. The qualitative analysis of organic compounds involves the detection of all these major elements present in it with the help of suitable chemical tests. The elements other than C, H and O are called extra elements. The elements are usually tested in the form of ions. Since organic compounds are covalent in nature, they do not ionize. Therefore, to convert elements, present in organic compounds into ions, the organic, is plunged in distilled with sodium metal which is The filtrate is called Lassaignes extract (L.E.) or sodium extract.

  • Detection of Nitrogen
    Sodium fusion extract is reacted with iron sulphate. This is then acidified with concentrated sulphuric acid and formation of prussian blue colour shows the presence of nitrogen. This process occurs in three steps as mentioned below:
    \begin{array}{r}{\text { FeSO}_{4}+2 \mathrm{NaOH} \longrightarrow \mathrm{Fe}(\mathrm{OH})_{2}} \, +\mathrm{{Na}_{2} \mathrm{SO}_{4}}\end{array}
    \begin{array}{c}{\mathrm{Fe}(\mathrm{OH})_{2}+6 \mathrm{NaCN} \longrightarrow} \, {\mathrm{Na}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]+2 \mathrm{NaOH}}\end{array}
    \begin{array}{c}{3 \mathrm{Na}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]+4 \mathrm{FeCl}_{3} \longrightarrow}\, {\mathrm{Fe}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]_{6}+12 \mathrm{NaCl}}\end{array}

 

  • Detection of Sulphur
    In this case, sodium extract is reacted with acetic acid and then lead acetate is added. Thus formation of black precipitate of lead sulphide shoes the presence of sulphur. The process occurs as follows:
    \begin{array}{c}{\mathrm{Na}_{2} \mathrm{S}+\mathrm{Na}_{2}\left[\mathrm{Fe}(\mathrm{CN})_{5} \mathrm{NO}\right] \rightarrow} \, {\mathrm{Na}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{5} \mathrm{NOS}\right]}\end{array}
    \begin{array}{c}{\mathrm{Na}_{2} \mathrm{S}+\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2} \mathrm{Pb}\, \overset{CH_{3}COOH}{\rightarrow}\mathrm{PbS\downarrow}+2 \mathrm{CH}_{3} \mathrm{COONa}}\end{array}

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  • Detection of Halogens
    In this process, sodium fusion extract is acidified with nitric acid and then treated with silver nitrate. Now, if a white precipitate forms then it indicates the presence of chlorine or if a yellowish precipitate indicates the presence of bromine or iodine. The process occurs as follows:
    \mathrm{NaX}+\mathrm{AgNO}_{3} \stackrel{\mathrm{HNO}_{3}}{\longrightarrow} \mathrm{AgX} \downarrow
    \mathrm{AgCl}+2 \mathrm{NH}_{3(a q)} \longrightarrow\left[\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}\right] \mathrm{Cl}

 

Physical Chemistry

Quantitative Analysis
A quantitative analysis is one in which the amount or concentration of a particular species in a sample is determined accurately and precisely. Basically, it is the determination of the percentage composition of elements in a particular compound.

 

Volumetric Analysis
Volumetric analysis is a process by which the concentration or strength of an unknown chemical solution is measured by measuring the volume of 
its solution taking part in a given chemical reaction. The main process of this analysis is called titration.
 

Titration: Determination of strength of one solution using another solution of known strength under volumetric conditions is known as titration.

 

Some important terms used in volumetric analysis

  • Titrant: The solution of known strength (which is taken in the burette is called titrant.

  • Titrate: The substance whose concentration is to be determined by titration is called titrant.

  • Equivalence point: It is the point where the reaction between two solutions is the point where reaction in a titration at which the quantity of titrant is exactly sufficient for the completion of stoichiometric reaction to being completed with titrate. At this point, there is a sudden change in a physical property, such as indicator colour, pH, conductivity.

  • Indicator: A compound having a physical property (usually colour) that changes abruptly near the equivalence point of a chemical reaction is known as an indicator. It indicates the attainment of endpoint.

  • Standard solution: A solution whose concentration is known is called a standard solution.

  • Standardization: It is the process in which the concentration of reagent is determined by reaction with a known quantity of the second reagent whose concentration is known.

  • Primary standard substance: A reagent that is pure enough so that its standard solution can be prepared directly by dissolving a definite weight of it in a definite volume of solvent is known as the primary standard, e.g., crystalline oxalic acid, Mohr's salt, etc.

  • Secondary standard substance: The substance or reagent whose standard solution cannot be prepared directly is called secondary standard, examples include KMnO4, NaOH, KOH, etc.

  • Redox titrations: These titrations proceed with the transfer of electrons among the reacting ions in aqueous solutions.

  • Acid-base titrations: In acid-base titration, the strength of an acid or base is determined by titrating it against a standard solution of base or acid respectively. It involves neutralisation reaction.
    \mathrm{H}^{+}+\mathrm{OH}^{-} \longrightarrow \mathrm{H}_{2} \mathrm{O}

  • Titration of Mohr's salt vs KMnO4:
    \begin{array}{c}{2 \mathrm{KMnO}_{4}+8 \mathrm{H}_{2} \mathrm{SO}_{4}+10 \mathrm{FeSO}_{4}\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4} \cdot 6 \mathrm{H}_{2} \mathrm{O}}\, {\longrightarrow \mathrm{K}_{2} \mathrm{SO}_{4}+2 \mathrm{MnSO}_{4}+5 \mathrm{Fe}_{2}\left(\mathrm{SO}_{4}\right)_{3}+} {10\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}+68 \mathrm{H}_{2} \mathrm{O}}\end{array}

 

How to prepare for Principles Related to Practical Chemistry

  • This chapter is part of organic chemistry. All the basic methods and techniques covered in this chapter.
  • For preparing this chapter, there is no need of any pre-requisite chapter. Thus prepare it freshly and actively.
  • All the techniques and methods are discussed for qualitative and quantitative estimation of elements.
  • In the nutshell, it can be said that although this chapter is not very long, it is a very simple and straightforward one. So always say a "Big YES" to this chapter.

 

Prescribed Books

For this chapter, first, the NCERT book is best for initial level preparation as well as for board exams. Now, after this, if you want to prepare for competitive exams like JEE and NEET, then these are the best books for you - O.P Tandon. Meanwhile, in the preparation, you must continuously give the mock tests for the depth of knowledge. Our platform will help you to provide with the variety of questions for deeper knowledge with the help of videos, articles and mock tests.

 

Chemistry Chapter- wise Notes for Engineering and Medical Exams

Chapters No.

Chapters Name

Chapter 1

Some basic concepts in chemistry

Chapter 2

States of matter

Chapter 3

Atomic Structure

Chapter 4

Solutions

Chapter 5

Chemical Thermodynamics

Chapter 6

Equilibrium

Chapter 7

Redox Reaction and Electrochemistry

Chapter 8

Chemical kinetics

Chapter 9

Surface Chemistry

Chapter 10

General Principle and processes of Isolation of metals

Chapter 11

Classification of Elements and Periodic table

Chapter 12 

Hydrogen

Chapter 13

p- block Elements

Chapter 14 

s-block Elements (Alkali and Alkaline Earth Metals)

Chapter 15 

Chemical Bonding and Molecular Structure

Chapter 16

d- and f- BLOCK ELEMENTS

Chapter 17

Coordination Compounds

Chapter  18 

Environmental Chemistry

Chapter 19

Purification and Characterisation of Organic Compounds

Chapter 20

Some Basic Principles of Organic Chemistry

Chapter 21

Hydrocarbons

Chapter 22

Organic Compounds containing Halogens

Chapter 23

Organic Compounds containing Oxygen

Chapter 24

Organic Compounds Containing Nitrogen

Chapter 25

Polymers

Chapter 26

Biomolecules

Chapter 27

Chemistry in Everyday Life

Topics from Principles Related to Practical Chemistry

  • Detection of extra elements (N,S, halogens) in organic compounds ( JEE Main, MET ) (8 concepts)
  • Chemical principles involved in the qualitative salt analysis: Cations - Pb2+, Cu!+, Af,+, Fe1+, Zn2+, Ni2+, Ca2+, Ba2+, Mg2+, NH. Anions- CO,", S2~, SO2-, NO", NO~2, Cf, Br", I" ( JEE Main, MET ) (24 concepts)
  • Chemistry involved in the titrimetric excercises -Acids bases and the use of indicators, oxalic-acid vs KMnO,, Mohr's salt vs KMnO ( JEE Main, MET ) (5 concepts)
  • Detection of the following functional groups: hydroxy! (alcoholic and phenolic), carbonyl (aldehyde and ketone), carboxyl and amino groups in organic compounds ( JEE Main, MET ) (11 concepts)
  • Organic compounds: Aeetanilide, pnitroacetanilide, aniline yellow, iodoform ( JEE Main, MET ) (1 concepts)
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