Strength of Solutions

1. Strength of Solutions

The amount of solute dissolved per unit solution or solvent is called Strength of solution. There are various methods of measuring strength of a solution. :

1. Mass Percentage (%w/w):
“It represents mass of a component present in 100 g of solution”

Mass% of a component = Mass of the component in the sol. *100/Total Mass of sol


2. Volume percentage (%v/v): 

“It represents volume of a component in 100 mL of solution” 

 Vol. % of a component = Vol. of component ×100 /Total vol. of solution

3. Mass by volume percentage (%w/v): 

“It represents mass of solute in grams present in 100 mL of solution” 

Mass by vol. percent = Mass of solute in gram *100/Vol. of sol.in ml  

4. Parts per Million (ppm): 

"Concentration in parts per million can be expressed as mass to mass, volume to volume and mass to volume."

Parts per Million = (No. of parts of the component/Total no. of all the components of sol.)*10⁶ 

5. Mole Fraction (x) :
“It represents the moles of a solute present in one mole of solution”

Mole fraction=No. of moles of the component/Total no. of moles all the components 

For example, in a binary mixture, if the number of moles of A and B are n_A and n_B respectively, the mole fraction of A will be

x_A =n_{A/nA + nB}

6. Molarity, M:
 “It represents moles of solute present in 1 L of solution”

 Molarity, M = Moles of solute / Vol. of sol. in L

Units of Molarity are mol/L also represented by ‘M’ or ‘Molar’. 

“Density of a solution = mass of the solution per unit volume”

  Density, d = m / V 

7. Molality, m:
“It represents moles of solute present per kg of solvent”

Molality, m = Moles of solute/Mass of solvent in kg

Units of molality are mol/kg which is also represented by ‘m’ or ‘molal’

8. Normality, N

It represents no. of equivalents of solute present in 1 L of solution.

Normality, N = No. of Equivalents of solute/Vol. of sol. in L

No. of equivalents, eq = Weight/Equivalent weight (W / E)


E=M/z(z is the valency factor)

SOME IMPORTANT RELATIONSHIPS

Dilution Law

If a solution is diluted by adding solvent to it, then the amount of solute remains constant and we can write:

M₁V₁ = M₂V₂ and N₁V₁ = N₂V₂


Molarity and Normality 

Normality = z × Molarity]


IMPORTANT : 

Mass %, ppm, mole fraction and molality are independent of temperature, whereas molarity & normality are a function of temperature. This is because volume depends on temperature and the mass does not.