Molarity, molality normality , formality
Molarity (M) is defined as the number of moles of solute per litre of solution.
molarity = moles of solute/litres of solution
Molality (m) is defined as the number of moles of solute per kilogram of solvent.
molality = moles of solute/kilograms of solvent
Molarity is a measurement of the moles in the total volume of the solution, whereas molality is a measurement of the moles in relation to the mass of the solvent.
When water is the solvent and the concentration of the solution is low, these differences can be negligible (d = 1.00 g/mL). However, when the density of the solvent is significantly different than 1 or the concentration of the solution is high, these changes become much more evident.
Example:
Compare the molar and molal volumes of 1 mol of a solute dissolved in CCl4 (d = 1.59/mL).
For a 1 Molar solution, 1 mol of solute is dissolved in CCl4 until the final volume of solution is 1 L.
For a 1 molal solution, 1 mol of solute is dissolved in 1 kg of CCl4.
1 kg of CCl4 × (1,000 g/1 kg) × (mL/1.59 g) = 629 mL CCl4
Normality (N) is defined as the number of mole equivalents per litre of solution:
normality = number of mole equivalents/1 L of solution
Like molarity, normality relates the amount of solute to the total volume of solution; however, normality is specifically used for acids and bases. The mole equivalents of an acid or base are calculated by determining the number of H+ or OH- ions per molecule:
N = n × M (where n is an integer)
For an acid solution, n is the number of H+ ions provided by a formula unit of acid.
Example:
A 3 M H2SO4 solution is the same as a 6 N H2SO4 solution.
For a basic solution, n is the number of OH- ions provided by a formula unit of the base.
Example:
A 1 M Ca(OH)2 solution is the same as a 2 N Ca(OH)2 solution.
The formality of a solution may be defined as the number of gram formula masses of the ionic solute dissolved per litre of the solution. Commonly, the term formality is used to express the concentration of the ionic solids which do not exist as molecules but exist as a network of ions.
Molarity (M) is defined as the number of moles of solute per litre of solution.
molarity = moles of solute/litres of solution
Molality (m) is defined as the number of moles of solute per kilogram of solvent.
molality = moles of solute/kilograms of solvent
Molarity is a measurement of the moles in the total volume of the solution, whereas molality is a measurement of the moles in relation to the mass of the solvent.
When water is the solvent and the concentration of the solution is low, these differences can be negligible (d = 1.00 g/mL). However, when the density of the solvent is significantly different than 1 or the concentration of the solution is high, these changes become much more evident.
Example:
Compare the molar and molal volumes of 1 mol of a solute dissolved in CCl4 (d = 1.59/mL).
For a 1 Molar solution, 1 mol of solute is dissolved in CCl4 until the final volume of solution is 1 L.
For a 1 molal solution, 1 mol of solute is dissolved in 1 kg of CCl4.
1 kg of CCl4 × (1,000 g/1 kg) × (mL/1.59 g) = 629 mL CCl4
Normality (N) is defined as the number of mole equivalents per litre of solution:
normality = number of mole equivalents/1 L of solution
Like molarity, normality relates the amount of solute to the total volume of solution; however, normality is specifically used for acids and bases. The mole equivalents of an acid or base are calculated by determining the number of H+ or OH- ions per molecule:
N = n × M (where n is an integer)
For an acid solution, n is the number of H+ ions provided by a formula unit of acid.
Example:
A 3 M H2SO4 solution is the same as a 6 N H2SO4 solution.
For a basic solution, n is the number of OH- ions provided by a formula unit of the base.
Example:
A 1 M Ca(OH)2 solution is the same as a 2 N Ca(OH)2 solution.
The formality of a solution may be defined as the number of gram formula masses of the ionic solute dissolved per litre of the solution. Commonly, the term formality is used to express the concentration of the ionic solids which do not exist as molecules but exist as a network of ions.
