# 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

Disclaimer: Compete.etutor.co may from time to time provide links to third party Internet sites under their respective fair use policy and it may from time to time provide materials from such third parties on this website. These third party sites and any third party materials are provided for viewers convenience and for non-commercial educational purpose only. Compete does not operate or control in any respect any information, products or services available on these third party sites. Compete.etutor.co makes no representations whatsoever concerning the content of these sites and the fact that compete.etutor.co has provided a link to such sites is NOT an endorsement, authorization, sponsorship, or affiliation by compete.etutor.co with respect to such sites, its services, the products displayed, its owners, or its providers.

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}