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Sunday, February 19, 2017

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.



xA→ Mole Fraction of solvent
xB → Mole fraction of solute
nA → No:of moles of solvent.
nB → No:of moles of solute.
Mole Fraction of the solution = xA + xB = 1

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