 # Laws of chemical combination and Atomic and molecular masses

Laws of Chemical Combination :

• Law of conservation of mass (Lavoisier)
• Law of constant proportions
• Law of multiple proportions
• Law of reciprocal proportions
• Law of gaseous volumes.

\tt Relative \ atomic \ mass = \frac{mass \ of \ an \ atom \ of \ element}{mass \ of \ an \ atom \ of \ H}
(or) \tt Relative \ atomic \ mass = \frac{mass \ of \ an \ atom \ of \ element}{\frac{1}{16} \times mass \ of \ an \ atom \ of \ O}

\tt Average \ atomic \ mass = \frac{\sum\left(\% \ of \ abundance \ \times isotopic \ mass\right)}{100}

Dulong–Petits law : According to this law, for metals
\tt Atomic \ mass \times specific \ heat \ \simeq 6.4

Molecular mass and Formula mass :
molecular mass = (x × atomic mass of A) + (y × atomic mass of B) + (z × atomic mass of C)
eg : C6H12O6 = 180.162 U

Formula mass : eg : NaCl, formula mass = (23.0 + 35.5) = 58.5 U

Equivalent mass :
\tt E_{element} = \frac{Atomic \ mass \ of \ element}{Valence \ of \ element}

Equivalent mass of an ion :
\tt E_{ion} = \frac{Formula \ mass \ of \ ion}{Charge \ on \ ion \ (without -ve (or) +ve)}

Equivalent mass of a salt :
\tt E_{salt} = \frac{Formula \ mass \ of \ salt}{total \ positive \ (or) \ negative \ charge \ on \ cationic (or) \ anionic \ part}

Equivalent mass of an acid :
\tt E_{Acid} = \frac{M_{Acid}}{Basicity}
Equivalent mass of a base :
\tt E_{base} = \frac{M_{base}}{Acidity}

\tt E_{Oxidant (or) \ Reductant} = \frac{M_{Oxidant (or) \ Reductant}}{No.of \ electrons \ lost \ or \ gained \ by \ one \ molecule \ of \ oxidant \ or \ reductant}

### Part2: View the Topic in this Video from 0:12 to 14:56

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1.  \tt Atomic \ mass \ = \ \frac{Average \ mass \ of \ an \ atom}{1/12 \times Mass \ of \ an \ atom \ of \ C^{12}}

2. \tt Number \ of \ gram \ atoms \ = \ \frac{Mass \ of \ an \ element \ in \ grams}{GAM}

3. \tt Number \ of \ atoms \ in \ 1gm \ of \ element \ = \ \frac{6.02 \times 10^{23} }{Atomic \ mass}

4. Atomic mass × Specific heat (cal / gram) = 6.4 (approx)

5. Atomic mass = Equivalent mass × Valency

6. \tt Valency \ of \ the \ element = \frac{Molecular \ mass \ of \ chloride}{Equivalent \ mass \ of \ chloride} \tt = \frac{2 \times Vapour \ density \ of \ chloride}{Equivalent \ mass \ of \ metal + 35.5}

7. \tt Molecular \ mass = \frac{Mass \ of \ one \ molecule \ of \ the \ substance}{1/12 \times Mass \ of \ one \ atom \ of \ C - 12}

8. \tt Density \ of \ a \ gas \ at \ NTP = \frac{Mol. \ mass \ in \ gm.}{22400 \ mL}

9. \tt Minimum \ molecular \ mass = \frac{Atomic/molecular \ mass \ of \ minor \ component}{Mass \ of \ minor \ component \ per \ gram \ of \ macromolecule}