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Some Basic Concepts In Chemistry

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Some Basic Concepts in Chemistry PDF Notes, Important Questions and Formulas

Some Basic Concepts in Chemistry

 

Definition of mole:

One mole is a collection of that many entities as there are number of atoms exactly in 12 gm of C -12 isotopes.

Or 1 mole = Collection of 6.02×1023species

           6.02×1023=NA=Avogadro’s No.

1 mole of atoms is also termed as 1 gm-atom, 1 mole of ions is termed as 1 gm-ion and 1 mole of molecule termed as 1 gm-molecule.

Methods of Calculations of mole

a) If no. of some species is given, then no, of moles

             begin mathsize 12px style equals fraction numerator Given text  no. end text over denominator straight N subscript straight A end fraction end style     

b) If weight of a given species is given, then no of moles

begin mathsize 12px style table attributes columnalign left end attributes row cell equals fraction numerator Given text  wt end text over denominator Atomic text  wt end text end fraction left parenthesis for text  atoms end text right parenthesis comma end cell row cell Or text  = end text fraction numerator Given text  wt. end text over denominator Molecule text  wt end text end fraction left parenthesis for text   end text molecule right parenthesis end cell end table end style                

c) If volume of a gas is given along with its temperature

(T)and pressure(P)

  Use nbegin mathsize 12px style PV over RT end style

Where R=0.0821 lit-atm/mol-K (When P is in atmosphere an V is in litre.)

1 mole of any gas at STP (0℃ &1 bar) occupies 22.7 litres.

1 mole of any gas at STP (0ᵒ C & 1 atm) occupies 22.4 litres.

Atom: Atom is smallest particle which cannot be divided into its constituents.

Atomic weight: It is the weight of an atom relative to one twelvth of weight of 1 atom of C-12

Laws of chemical combination

(a) Law of conservation of mass [Lavoisier]

In chemical change total mass remains conserved i.e. mass before the reaction is always equal to mass after the reaction.

begin mathsize 12px style table attributes columnalign left end attributes row cell straight H subscript 2 plus 1 divided by 2 text  O end text subscript 2 text   end text rightwards arrow text  H end text subscript 2 straight O left parenthesis calligraphic l right parenthesis end cell row cell left parenthesis straight g right parenthesis text         end text left parenthesis straight g right parenthesis text      end text end cell end table end style

1 mole ½ mole        1 mole

Mass before the reaction=1×2+1/2×32=18gm

Mass after the reaction=1×18=18 gm

(b) Law of constant composition [Proust]

All chemical compounds are found to have constant composition irrespective of their method of preparation or sources.

⇒ In H2O, Hydrogen & oxygen combine in 2: 1 molar ratio, this ratio remains constant

Whether it is Tap water, river water or seawater or produced by any chemical reaction.

(c) Law of multiple proportional [Dalton]

When one element combines with the other element to form two or more different compounds, the mass of one element, which combines with a constant mass of the other bear a simple ratio to one another.

(d) Law of reciprocal proportions[Richter]

When two elements combine separately with definite mass of a third element, then the ratio of their masses in which they do so is either the same or some whole number multiple of the ratio in which they combine with each other. This law can be understood easily with the help of the following examples.

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