## Chemistry formulas for Atoms, Molecules and Chemical Arithmetic Part I

##
__Atomic Weight related Chemical
Formulas__

__Atomic Weight related Chemical Formulas__

·
Atomic Weight of an Element = Weight of an
average Atom of that Element/ (1/12)x Mass of an element of C

^{12}
·
1 a.m.u. = 1.66x10

^{-24}g
·
Atomic Weight = Gram Atomic Weight (GAW)

·
1 Gram
Atomic Weight (GAW) of every element contains 6.023x10

^{23}atoms of that element.
·
No. of gram of an element = weight of element in
gram/ Gram Atomic Weight (GAW) of that element

###
**Methods of Determining Atomic Weight**

####
i. **Dulong and Pettits Method:**

Applicable
only for solid elements except Be, B, C, Si.

·
Atomic Weight
x Specific Heat = 6.4 (app.)

·
Atomic Weight
(app.) = 6.4/ Specific Heat (in Calories)

·
Exact Atomic Weight = Equivalent Weight x
Valency

·
Valency = App. Atomic Weight / Equivalent Weight

####
ii. **Vapour Density Method:**

Applicable only
for those elements whose chlorides are volatile.

·
Valency of the Element = Molecular Weight of
Chloride / Equivalent Weight of Chloride

·
Valency of the Element = (2 x V.D. of Chloride)
/ (Equivalent Weight of Metal + 35.5)

Where, V.D. = Vapour Density

·
Atomic Weight = Equivalent Weight of Metal x
Valency

####
iii. **Specific Heat Method:**

Applicable only
for Gases.

·
Cp/Cv for monoatomic gases = 1.66

·
Cp/Cv for diatomic gases = 1.40

·
Cp/Cv for triatomic gases = 1.33

·
Atomic Weight of Gaseous Element = Molecular
Weight/ Atomicity

Where, Atomicity is number of atoms present in a molecule of a gaseous
element. For example atomicity of Inert Gas is 1, atomicity of Ozone is 3,
atomicity of H

_{2}N_{2}O_{2}X_{2}is 2, and atomicity of Sulphur is 8.####
**
iv. ****Volatile Chloride Formation Method:**

·
Atomic Weight of the Element = Equivalent Weight
(Z) x Valency (x)

####
v. **Isomorphism Method:**

This method based
on law of Isomorphism. According to law of Isomorphism, “Compounds having
identical crystal structure have similar constitution and chemical formula”

·
Atomic Weight = Equivalent Weight x Valency

·
Weight of Element A that combines with certain
weight of other elements/Weight of Element B that combines with the same weight
of other elements = Atomic Weight of A / Atomic Weight of B

##
__Molecular Weight related Chemical
Formulas__

__Molecular Weight related Chemical Formulas__

·
Molecular Weight = Weight of 1 Molecule of the
Substance/ (1/12)x Weight of 1 atom of C

^{12}
·
Actual Weight of 1 Molecule = Molecular Weight x
1.66x10

^{-24}g###
**Methods of Determining Atomic Weight**

####
**1.
****Diffusion
Method:**

Applicable only for gases.

·

Where, r

_{1}& r_{2}is rate of diffusion of gases and M_{1 }& M_{2}is Molecular Weight.####
**2.
****Vapour
Density Method:**

Applicable only for gases.

·
Molecular Weight = 2 x Vapour Density

####
**3.
****Victor
Mayer Method: **

**Applicable only for volatile liquids and solids.**

·
Molecular Weight of a substance = 22400 ml of
vapour of a substance at STP

##
__Equivalent Weight related Chemical
Formulas__

__Equivalent Weight related Chemical Formulas__

·
No. of Gram Equivalent Weight = Weight of the
substance in gram/ Gram Equivalent Weight of the substance

·
Equivalent Weight of an Element = Atomic Weight/
Valency

·
Equivalent Weight of an Acid = Molecular Weight/
Basicity

·
Equivalent Weight of an Base = Molecular Weight/
Acidity

·
Equivalent Weight of a Salt = Formula Weight/
Total Positive or Negative Charge

·
Equivalent Weight of a Reducing Agent = Formula
Weight/ No. of electrons lost per molecule or Total change in Oxidation Number

·
Equivalent Weight of an Oxidising Agent =
Formula Weight/ No. of electrons gained per molecule or Total change in
Oxidation Number

·
Equivalent Weight of Radicals = Formula Weight
of Radical/ No. of units of Charge

###
**Methods of Determining Equivalent
Weight**

####
**1.
****Hydrogen
Displacement Method:**

Applicable for metals which can displace or combine
with hydrogen.

·
Equivalent Weight of Metal = (Weight of metal x
1.008)/ Weight of Hydrogen Displaced

·
Equivalent Weight of Metal = (Weight of metal x
11200)/ Volume in ml of H

_{2}displaced at STP####
**2.
****Oxide
Formation Method:**

·
Equivalent Weight of Metal = (Weight of metal x
8)/ Weight of Oxygen

·
Equivalent Weight of Metal = (Weight of metal x
5600)/ Volume in ml of Oxygen at STP

####
**3.
****Chloride
Formation Method: **

·
Equivalent Weight of Metal = (Weight of metal x
35.5)/ Weight of Chlorine

·
Equivalent Weight of Metal = (Weight of metal x
11200)/ Volume in ml of Chlorine at STP

####
**4.
****Neutralization
Method: **

·
Equivalent Weight of Acid or Base = Weight
of acid or base in gram/ (Volume of base
or acid in litre required for neutralization x Normality of base or acid)

####
**5.
****Metal
Displacement Method: **

·
Weight of Metal Added W

_{1}/ Weight of Metal Displaced W_{2}= Equivalent Weight of Metal Added E_{1}/ Equivalent Weight of Metal Displaced E_{2}####
**6.
****Electrolytic
Method: **

·
Gram Equivalent Weight = Electrochemical
Equivalent x 96500

·
Weight of X deposited/ Weight of Y deposited =
Equivalent Weight of X/ Equivalent Weight of Y

####
**7.
****Double
Decomposition Method: **

·
Weight of Salt taken (W

_{1})/ Weight of ppt. obtained (W_{2}) = Equivalent Weight of Salt (E_{1})/ Equivalent Weight of Salt in ppt. (E_{2})####
**8.
****Conversion
Method: **

·
Weight of Compound A (W

_{1})/ Weight of Compound B (W_{2}) = (Equivalent Weight of Metal + Equivalent Weight of Anion of Compound A)/ (Equivalent Weight of Metal + Equivalent Weight of Anion of Compound B)####
**9.
****Volatile
Chloride Method: **

·
Equivalent Weight = {(2 x Vapour Density of
Chloride)/ Valency} – 35.5

####
**10.
****Silver
Salt Method: **

**Applicable for organic acids**

·
Equivalent Weight of Acid = Molecular Weight of
Acid/ Basicity