LAWS OF CHEMICAL COMBINATION

(a) Law of conservation of mass: "In all physical and chemical changes, the total mass of the reactants is equal to that of the products" or "matter can neither be created nor destroyed."

(b)Law of constant composition/definite proportion: "A chemical compound is always found to be made up of the same elements combined together in the same fixed ratio by weight".

(c) Law of multiple proportions: "When two elements combine together to form two or more chemical compounds, then the weight of one of the elements which combine with a fixed weight of the other bear a simple ratio to one another".

(d) Law of reciprocal proportions: The ratio of the weights of two elements A and B which combine with a fixed weight of the third element C is either the same or a simple multiple of the ratio of the weights of A and B which directly combine with each other. 

(e) Gay-Lussac's law of gaseous volumes: "When gases react together, they always do so in volumes which bear a simple ratio to one another and to the volumes of the products, if gaseous, all measurements are made under the same conditions of temperature and pressure".

BRANCHES OF CHEMISTRY

 The four main branches of chemistry are:

(1) Organic chemistry;          (2) Inorganic chemistry;

(3) Physical chemistry;         (4) Analytical chemistry.

(1) Organic chemistry: It is concerned with the study of compounds of carbon except carbonates, bicarbonates, cyanides, isocyanides, carbides and oxides of carbon. It is actually the study of hydrocarbons and their derivatives.

(2) Inorganic chemistry: It deals with the study of all known elements and their compounds except organic compounds. It is concerned with the materials obtained from minerals, air, sea and soil.

(3) Physical chemistry: It is concerned with the physical properties and constitution of matter, the laws of chemical combination and theories governing reactions. The effect of temperature, pressure, light, concentration, etc., on reactions come under the scope of physical chemistry.

(4) Analytical chemistry: It deals with various methods of analysis of chemical substances both qualitative and quantitative. It includes chemical and physical methods of analysis. A number of specialized branches have been introduced as to cope with the extraordinary expansion in the subject of chemistry.

 Some of the specialized branches are:

(i) Biochemistry: It comprises the studies of the substances related to living organisms and life processes.

(ii) Medicinal chemistry: It deals with the application of chemical substances for the prevention and cure of various diseases in living beings.

(iii) Soil and agriculture chemistry: It deals with the analysis and treatment of soils so as to increase its fertility for the better yields of crops. It is concerned with the chemicals used as fertilizers, insecticides, germicides, herbicides, etc.

(iv) Geochemistry: It includes the study of natural substances like ores and minerals, coal, petroleum, etc.

(v) Industrial chemistry: It deals -with the study of chemical processes for the production of useful chemicals on a large scale at relatively low costs.

(vi) Nuclear chemistry: It is the most recent branch. It includes the study of nuclear reactions, the' production of radioactive isotopes and their applications in various fields.

(vii) Structural chemistry: It deals with various techniques used for elucidation of the structure of chemical substances. It is concerned with the properties of substances in terms of their structure.

(viii) Polymer chemistry: It includes the study of chemical substances of very high molecular masses of the order of 100,000 or greater, called polymers-natural or artificial. 

(ix) Limnochemistry: It deals with the study of chemistry involved in the river water or water reservoirs.

(x) Phytochemistry: It includes the study of chemistry of plants.

GOLD NUMBER (SURFACE CHEMISTRY)

Gold number of a protective colloid is the minimum weight of it in milligrams which must be added to 10 mL of a substance (red gold sol) so that no coagulation of the gold sol takes place when 1 mL of 10% sodium chloride solution is rapidly added to it.

or

Weight of the dried protective agent in milligrams, which, when added to 10 mL of a standard gold sol (0.0053 to 0.0058%), is just sufficient to prevent a colour change from red to blue on the addition of 1 mL of 10% sodium chloride solution, is equal to the gold number of protective colloid. 

Protective power ∝ 1/Gold number

Note: Gold number is a practical value, it cannot be obtained theoretically.

SIGNIFICANT FIGURES

 (A) Every scientific observation involves some degree of uncertainty depending upon the limitation of instrument. To represent scientific data, role of significant figures has its own importance.

 (B) Significant figures are equal to the number of digits in numbers with last digit uncertain and rest all are certain digits i.e. all the digits of datum including the uncertain one , are called significant figures. 

(C) Rules for determination of significant figure:

 (i) All non zero digits are significant.

 Example : 3.14 has three significant figures 

(ii) The zeros to the right of the decimal point are significant.

 Example : 3.0 has two significant figures.

 (iii) The zeros to the left of the first non zero digit in a number are not significant.

 Example : 0.02 has one significant figure.

 (iv) The zeros between two non zero digits are also significant.

 Example : 6.01 has three significant figures. 

(v) Exponential form : N × 10 n . Where N show the significant figure.

 Example : 1.86 × 10 4 has three significant figure.

 (vi) Rounding off the uncertain digit : 

(a) If the left most digit to be rounded off is more than 5 , the preceding number is increased by one. 

Example : 2.16 is rounded to 2.2

 (b) If the left most digit to be rounded off is less than 5 , the preceding number is retained.

 Example : 2.14 is rounded off to 2.1 

(c) If the left most digit to be rounded off is equal to 5 , the preceding number is not changed if it is even and increased by one if it is odd. Example : 3.25 is rounded off to 3.2 2.35 is round off to 2.4

IUPAC NOMENCLAURE OF ORGANIC COMPOUNDS

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IUPAC NOMENCLATURE

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