These are important concentration terms used in chemistry to describe the amount of a substance in a given volume or mass of a solution. Each has its specific applications and units.

Normality (N)

Definition: Normality is the number of equivalents of solute per liter of solution. It is often used in acid-base chemistry and in redox reactions where the number of reactive units (equivalents) is important.

Equivalents: An equivalent is the amount of substance that reacts with or supplies one mole of hydrogen ions (H⁺) in acid-base reactions or one mole of electrons in redox reactions.

Example:

• For HCl (hydrochloric acid), which has one equivalent per mole: $\text{Normality}=\text{Molarity}$
• For H₂SO₄ (sulfuric acid), which has two equivalents per mole (since each mole of H₂SO₄ provides two H⁺ ions):$\text{Normality}=2\times \text{Molarity}$

Molarity (M)

Definition: Molarity is the number of moles of solute per liter of solution. It is the most commonly used concentration unit in chemistry.

Example:

• A 1 M solution of NaCl contains 1 mole of NaCl in 1 liter of solution.

Molality (m)

Definition: Molality is the number of moles of solute per kilogram of solvent. Unlike molarity, it is not affected by temperature changes because it is based on the mass of the solvent.

Example:

• A 1 m solution of NaCl contains 1 mole of NaCl in 1 kilogram of water.

Mole Fraction (χ)

Definition: Mole fraction is the ratio of the number of moles of a component to the total number of moles of all components in the mixture.

Example:

• In a solution with 2 moles of ethanol (C₂H₅OH) and 8 moles of water (H₂O), the mole fraction of ethanol is:
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• Summary

  1. Normality (N):

     • Used in acid-base and redox reactions.
     • Depends on the number of equivalents.
     • Units: equivalents per liter (eq/L).

  2. Molarity (M):

     • Most common concentration unit.
     • Depends on the volume of the solution.
     • Units: moles per liter (mol/L).

  3. Molality (m):

     • Independent of temperature.
     • Depends on the mass of the solvent.
     • Units: moles per kilogram (mol/kg).

  4. Mole Fraction (χ):

     • Ratio of moles of a component to the total moles in the mixture.
     • Unitless.