Laws of Chemical Combination:
Law of conservation of mass:
“For any chemical change total mass of active reactants are always equal to the mass of the product formed”
Law of constant proportions:
“A chemical compound always contains same elements in definite proportion by mass and it does
not depend on the source of compound”.
Law of multiple proportions:
“When two elements combine to form two or more than two different compounds then the different masses of one element B which combine with fixed mass of the other element bear a simple ratio to one another”
Law of reciprocal proportion:
“ If two elements B and C react with the same mass of a third element (A), the ratio in which they do so will be the same or simple multiple if B and C reacts with each other”.
Gay Lussac’s law of combining volumes:
“At given temperature and pressure the volumes of all gaseous reactants and products bear a simple whole number ratio to each other”.
Atomic and Molecular Masses:
Atomic Mass:
• Mass of an atom.
• Reported in atomic mass unit “amu” or unified mass “u”
• One atomic mass unit i.e. amu, is the mass exactly equal to one-twelfth the mass of one carbon- 12 atom.
Molecular Mass:
• Mass of a molecule of covalent compound.
• It is equal to the sum of atomic masses of all the elements present in the molecule.
Formula Unit Mass
• Mass of a molecule of an ionic compound
• It is also equal to the sum of atomic masses of all the elements present in the molecule
Mole Concept:
Mole:
• Unit of amount of substance.
• One mole amount of substance that contains as many particles or entities as there are atoms in exactly 12 g of the 12C isotope.
Molar mass:
• Mass of one mole of a substance in gram
• Molar mass in gram in numerically equal to atomic/molecular/formula mass in amu or u.
Mole fraction:-
Ratio of the moles of one component of the solution to the total number of moles of solution
Total mole fraction of all the components of a solution is equal to 1.
For binary solutions having two components A and B
Mole fraction of A
XA = (nA)/(nA+nB)]
Mole fraction of B
XB = (nB)/(nA+nB)]
or XB = 1- XA
Molarity(M):-
Number of moles of solute per 1000 mL of the solution.
M = (Number of moles of solute)/(Volume of solution in L)
Molality(m):-
number of moles of solute per 1000 gram of the solvent.
m = (Number of moles of solute)/(Weight of solvent in kg)
