Easy Notes On Introduction To Analytical Chemistry | Class 11 Chemistry

Analytical chemistry : The branch of chemistry which deals with the study of seperation, identification, qualitative and quantitative determination of the compositions of different substances, is called analytical chemistry.

Qualitative analysis is concerned with the detection of the presence or absence of elements in compounds and mixture of compounds.

Quantitative analysis deals with the determination of the relative proportions of elements in compounds and mixture compounds.

 Importance of analytical chemistry :

1. Chemical analysis is one of the most important methods of monitoring the composition of raw materials, intermediates and finished products, and also the composition of air in streets and premises of industrial plants.
2. In agriculture, chemical analysis is used to determine the composition of soils and fertilizers.
3. In medicine, to determine the composition of medicinal preparations.
4. Analytical chemistry has applications in forensic science, engineering and industry. Industrial process as a whole and the production of new kinds of materials are closely associated with analytical chemistry. 

Analysis : Analysis is carried out on a small sample of the material to be tested, and not on the entire bulk.

 Semi-microanalysis: When the amount of a solid or liquid sample is a few grams, the analysis is called semi-microanalysis. 

Types of analysis :  

1. Qualitative Analysis and 2. Quantitative Analysis

a) Classical Methods :

Classical qualitative analysis methods : Classical qualitative analysis methods include separations such as precipitation, extraction and distillation.

Identification may be based on differences in colour, odour, melting point, boiling point, and reactivity.

Classical quantitative methods : Classical quantitative methods consist of volumetric analysis, gravimetric analysis, etc.  

b) Chemical Methods :

Chemical methods of qualitative analysis : Chemical analysis of a sample is carried out mainly in two stages : By Dry Method and Wet Method

In the dry method the sample under test is not dissolved and dry method is usually used as preliminary tests in the qualitative analysis.

In the wet method the sample under test is first dissolved and then analyzed to determine its composition. 

 The qualitative analysis of organic and inorganic compounds: The majority of organic compounds are composed of a relatively small number of elements. The most important ones are : carbon, hydrogen, oxygen, nitrogen, sulphur, halogen, phosphorous. Elementary qualitative analysis is concerned with the detection of the presence of these elements. The identification of an organic compound involves tests such as detection of functional group, determinition of melting/ boiling point, etc.

The qualitative analysis of simple inorganic compounds involves detection and confirmation of cationic and anionic species (basic and acidic radical) in them.

Chemical methods of quantitative analysis : 

Quantitative analysis of organic compounds involves methods such as (i) determination of percentage constituent element, (ii) concentrations of a known compound in the given sample, etc.

Quantitative analysis of simple inorganic compounds involves methods based on (i) decomposition reaction (gravimetric analysis), and (ii) the progress of reaction between two solutions till its completion (titrametric or volumetric analysis), etc.

The quantitative analytical methods involve measurement of quantities such as mass and volume, by means of some equipment/ apparatus such as weighing machine, burette.

Mathematical operation and error analysis : The accuracy of measurement is of a great concern in analytical chemistry. Also there can be intrinsic errors in the analytical measurement. The numerical data, obtained experimentally, are treated mathematically to reach some quantitative conclusion. In the following subsection we will consider these aspects related to measurments and calculation.

• Scientific notation (exponential notation) :

eg. 1)  602,200,000,000, 000, 000, 000, 000 = 6.022 x 10^23

      2)  123.546 = 1.23546 x 10^2

Ques. Express the following quantities in exponential terms. 

a. 0.0003498      b. 235.4678      c. 70000.0       d. 1569.00

 

• Some solved examples on addition, subtraction and multiplication 

Addition

Subtraction

Multiplication

 

Question : 

 Precision and accuracy of measurement : Nearness of the measured value to the true value is called the accuracy of measurement. Larger the accuracy smaller the error.

Errors may be expressed as absolute or relative error. 

Absolute error = Observed value - True value 

Relative error is generally a more useful quantity than absolute error.

Relative error is the ratio of an absolute error to the true value. It is expressed as a percentage.