Tips and Tricks for Chemical Arithmetic
1. Law of conservation of mass does not hold good for nuclear reactions.
2. Law of definite proportions do not hold good for non-stoichiometric compounds e.g., Wusitite Fe0.95O.
3. Law of definite proportions, law of multiple proportions and law of reciprocal proportions do not hold good when same compounds is obtained by using different isotopes of te same element e.g. H2O and D2O.
4. The term atom was introduced by Ostwald and the term molecule was introduced by Avogadro.
5. The concept of element was introduced by Robert Boyle.
6. The number of atoms present in a molecule of a gaseous element is called Atomicity.
7. Both atomic mass and molecular mass are just rations and hence have no units.
8. 1 mol of H2O # 22400 cc of H2O (because it is a liquid). Instead,
1 mol of H2O = 18cc of H2O
(because density of H2O = 1 g/cc)
9. 1 M H2SO4 = 2NH2SO4.
10. Minimum molecular mass of a macromolecular substance can be calculated by analysing it for one of the minar components. Minimum molecular mass is obtained when it is supposed that one molecule of the macromolecule contains only one atom or molecule of the minor component.
Minimum molecular mass
= Atomic/molecular mass of minor component/Mass of minor component per gram of macromolec ule