Page 11 - PC 101 practical notes 24-25..

MANSOURA NATIONAL UNIVERSIY
PHARM D- CLINICAL PHARMACY LEVEL I PHARM. ANAL. CHEM. I (PC 101)

Methods of expressing the concentration of standard solutions:

The most common methods are: Molarity (M) & Normality (N).

1. Molarity or Molar concentration (M):

= The number of moles of the solute per 1 liter of the solution.

Example: 0.5 M NaOH means 0.5 mole of NaOH / 1 L solution.

N.B. Molar solution is a solution that contains 1 mole of the solute

per 1 liter of the solution (i.e.: Molar solution = 1 M solution).

Remember:

Very Important
Definition of Mole (mol.):

For molecules:

The Mole means gram-molecular weight {i.e. Molecular wt. expressed in grams}.

Example: M.W. of NaOH = 40  1 mole of NaOH ≡ 40 g NaOH.

(i.e. The weight of 1 mole of NaOH is 40 g)
For atoms:

The Mole means gram-atomic weight {i.e. Atomic wt. expressed in grams}.

Example: A.W. of Na = 23  1 mole of Na ≡ 23 g Na.

(i.e. The weight of 1 mole of Na is 23 g)

2. Normality or Normal concentration (N):

= The number of equivalent weights of the solute per 1 liter of the solution.

Example: 2 N NaOH means 2 equivalent weights of NaOH / 1 L solution.

N.B. Normal solution is a solution that contains 1 equivalent weight of the

solute per 1 liter of the solution (i.e.: Normal solution = 1 N solution).

General definition of the equivalent weight of a substance:

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