Some basic concepts of chemistry

Chemistry the branch of science which deals with the study of matter and its properties.Importance of chemistryChemistry has played a major role in the development of medical science by developing required substances for treatment of diseases.Chemistry has influenced the present day lifestyle.Chemistry faces a stiff challenge of environmental consequences of recent developments in chemistry.

MATTER ANYTHING THA THAS MASS AND OCCUPIES SPACE IS CALLED MATTER.THERE ARE THREE MAJOR STATES OF MATTER SOLID, LIQUID AND GAS.SOLIDS HAVE DEFINITE SHAPE AND FIXED VOLUME.LIQUID HAVE FIXED VOLUME BUT INDEFINITE SHAPE.IN GASES BOTH THE VOLUME AND SHAPE ARE INDEFINITE.

Mole concept 1 mole of any substance refers to the presence as many entities as in the Avogadros constant which is equal to 6.022 x 1023. It has major application in chemistry and is used in quantitative analysis of compounds. 1 mole of any substance =6.022 x 1023 atoms/molecules/ions 1 mole = 22.4 L for any gas at STP or NTP. Atomic mass of a substance is equal to the molar mass of the substance which is the sum of protons and neutrons present in the atom of the substance. Atomic number indicates the number of electrons present in the atom of the element. Value of 1 atomic mass unit is the mass of one atom of C-12 isotope of carbon. 1 atomic mass unit = 1.66 x 10-24 g. There are seven base units in the SI unit system out of which one is mole. It indicates the amount of matter in a substance. The value of 1 mole is indicated by Avogadros constant.

Law of Equivalence The law of equivalence states that the equivalence of the reactant is same to the equivalence of product in a chemical reaction whether the reactant is neutralized, oxidized or reduced. We find this concept extremely useful in determining gram quantity of participants of the reaction.

Concentration terms 1. Molarity - It refers to the number of moles of solute present in 1L volume of the solution.

2. Molality It refers to the number of moles of solute present in 1 kg mass of solvent.

3. Mole Fraction It is defined as the ratio of number of moles of a component in a solution to the total number of moles in the solution. The component can be solute or solvent.

4. 5. Equivalent weight It refers to the weight of a substance required to directly or indirectly combine or replace 1 part by mass of hydrogen, 8 parts by mass of oxygen, 35.5 parts by mass of chlorine, 80 parts by mass of bromine, 127 parts by mass of Iodine, 17 parts by mass of 1 OH formula unit, etc. in a chemical reaction.6. Normality The number of gram equivalents of solute present in 1 L volume of the solution.

7. Mass Fraction It refers to the mass of a component of a solution solute or solvent present in total mass of solution.

Avogadros Hypothesis Under similar conditions of temperature and pressure the equal volumes of all gases contain same number of molecules or same number of moles.

LAW OF CHEMICAL COMBINATION

1. LAW OF CONSERVATION OF MASSIt states that the mass of reactants is directly equal to mass of products in a chemical reaction or mass can neither be created nor be destroyed in a chemical reaction.

2. LAW OF CONSTANT PROPORTIONSIt states that the compounds are formed when elements combine in a fixed ratio by mass.It was given by J. Proust.

3. GAY LUSSACS LAW OF COMBINING VOLUMESIt states that the under similar conditions of temperature and pressure equal no. of moles of all gases have equal no. of molecules.4.AVOGADROS HYPOTHESISIt states that under similar conditions of temperature and pressure there are equal number of moles or molecules of equal volumes of all gases.

4. DALTONS ATOMIC THEORYIt states that atom is the smallest indivisible particle of matter.Atom can neither be created nor be destroyed.Atoms of same element are identical in all respects.Atoms of different elements are different in all respects.Atoms combine in a fixed ratio by mass to form new substances.

Percentage composition 1. Mass % =

Empirical formula: The simplest whole number ratio of the atoms present in the compound.Molecular formula: The expression denoting the number of constituting elements and their atoms in the compound.

Steps to determine empirical formula and molecular formula from mass %

1. Convert the mass % given to grams.2. Convert the grams into number of moles of each element.3. Divide the mole value obtained above with the smallest number.4. Obtain the simplest ration to form empirical formula.5. To write molecular formula write the molar mass of the empirical formula of the compound.6. Divide the actual molar mass with the value obtained in previous step to get a number n.7. Multiply the empirical formula element with n to get the molecular formula.

Limiting reagent

It is the substance which is completely consumed during the chemical reaction.The substance which is not completely consumed is called excess reagent.It decides the amount of product to be formed in the chemical reaction.

Thermal stabilityIn this we check whether the compound is resistant to heat supplement or not.The thermally unstable compounds which are formed as a result of combination of a small anion or large anion with small cation or large cation.The thermally stable compounds are formed as a result of small cation and large cation or anion.

Oleum It refers to the solution of H2SO4 + SO3 .