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Gravimetric Analysis

Gravimetric analysis is an analytical technique based on the measurement of mass of solid substances and/or volume of gaseous species.
 
The gravimetric analysis is broadly classified into three heads:
  1. Mass–mass relationship: This relates the mass of a species (reactant or product) with the mass of another species (reactant or product) involved in a chemical reaction.
  2. Massvolume relationship: This establishes the relationship between the mass of a species (reactant or product) and the volume of a gaseous species (reactant or product) involved in a chemical reaction.
  3. Volume–volume relationship: This relationship deals with the volume of a gaseous species (reactant or product) with the volume of another gaseous species (reactant or product) involved in a chemical reaction.

Molarity (M)

Let the weight of solute be w gram, molar mass of solute be M1 g/mol, and the volume of solution be V liter.
 
Molarity Description: 11696.png
 
Number of moles of solute = Description: 11709.png = M × V (in liter)

Normality (N)

Let the weight of solute be w gram, equivalent mass of solute be E g/eqv., and the volume of solution be V liter. Therefore,
Description: 11728.png
 
Number of equivalents of solute = Description: 11737.png = N × V (in liter)

Equivalent mass

Equivalent mass = Description: 11744.png
 
∴ Number of equivalents of solute Description: 11752.png
 
∴ Number of equivalents of solute = n × Number of moles of solute
 
Also, Description: 11760.png N = M × n
 
∴ Normality of solution = n × molarity of solution

Dilution effect

When a solution is diluted, the moles and equivalents of solute do not change, but molarity and normality changes. While taking out a small volume of solution from a larger volume, the molarity and normality of the solution do not change, but moles and equivalents change proportionately.

Law of equivalence

According to the law of equivalence, whenever two substances react, the equivalents of one will be equal to the equivalents of other and the equivalents of any product will also be equal to that of the reactant.
 
In general, whenever two substances react with their n-factors in the ratio of a : b, then their molar ratio in a balanced chemical reaction would be b : a.




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