Mole Concept and Molar Mass

One mole is the amount of a substance that contains as many entities or particles as there are atoms in exactly 12 g of the carbon-12 isotope.

or

One mole is the amount of substance which contains 6.022 ×10²³ (avogadro's number) particles/entities (such as atoms, molecules or ions).

e.g.

• 1 mole of nitrogen atoms = 6.022 ×10²³ atom of nitrogen
• 1 mole of water molecules = 6.022 ×10²³ molecule of water. 
• 1 mole of sodium bromide = 6.022 ×10²³ formula unit of NaBr.

\[\mathrm{n=\frac{Mass~of~a~substance}{Molar~mass~of~a~substance}}\]

\[\mathrm{Number of Moles of Gas=\frac{Volume~of~the~gas~at~STP}{Molar~mass~of~a~substance}}\]

Mass % of a Component (w/w) \[=\frac{\text{Mass of the component in the solution}}{\text{Total mass of the component}}\times100\]

\[\mathrm{Molarity~}(M)=\frac{\text{Number of moles of solute}}{\text{Volume of solution (in L)}}\]

\[\mathrm{Normality~}(N)=\frac{\text{Number of gram equivalents}}{\text{Volume of solution (in L)}}\]

\[\mathrm{Molality~}(m)=\frac{\text{Moles of solute}(n)}{\text{Mass of solvent}(W_A)\mathrm{~in~kg}}\]

• The molar mass of any element in grams is numerically equal to its atomic mass in u.
• For polyatomic molecules, molar mass in grams equals the molecular or formula mass in u.
• "1 mole oxygen atoms" and "1 mole oxygen molecules" are NOT the same — always specify what entities you are counting.
• Earlier, the unit amu was used; it has been replaced by u (unified atomic mass unit).