Concentrations of the Solution

Concentrations of the solution can be expressed as:

1. Molarity: No: of moles of solute present in one liter solution.

Units: mol L¯¹

 

Ex: 0.5 M ethanol means 0.5 moles of ethanol dissolved in one liter.

2. Mass percentage (w/w) = 

Ex: a solution of 20% salt in water by mass means: 20g of salt + 80g water = 100g solution.

3. Volume percentage (v/v) = 

Ex: a solution of 20% ethanol in water by volume or 20% (v/v) ethanol in water means: 20ml ethanol + 80ml water = 100ml solution.

4. Mass by volume percentage (w/v) = mass of solute dissolved in 100ml solution. 

Units: g/ml

5. Parts per million (ppm) = 

So, 20ppm of NaOH in sea water means, 20mg in 10⁶ mg of water i.e. 1kg of sea water

6. Normality:  No. of gram equivalents present in one Liter of solution.

Units: g/l

n = no. of gram equivalents = wt/ GEW

G.E.W = gram equivalent weight

G.E.W = gram molecular weight/ n factor 

n factor:

⇒ For acids, n-factor is defined as the number of H⁺ ions replaced by 1 mole of acid in a reaction.

⇒ For bases, n-factor is defined as the number of OH¯ ions replaced by 1 mole of base in a reaction.

⇒ For salts, total number of positive or negative charge.

⇒ In case of redox reactions, for oxidizing or reducing agent = change in oxidation state per molecule of reactant (or) total number of electrons transferred per mole of reactant.

7. Molality: No. of moles of solute present in 1 Kg of the solvent. Units: mol/Kg

8. Mole Fraction: It is the ratio of the number of moles of one compound to the total number of moles of the solution.

x_A→ Mole Fraction of solvent

x_B → Mole fraction of solute

n_A → No:of moles of solvent.

n_B → No:of moles of solute.

Mole Fraction of the solution = x_A + x_B = 1