Practical Biochemistry for Students Varun Kumar Malhotra
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Methods of Expressing Concentration1

Concentration may be defined as weight per unit volume.
The most common expressions are:
  1. Percent
  2. Molarity
  3. Normality
  4. Molality
  5. Formality.
  1. Percent
    According to Caraway there are three ways of expressing percentage of solution, i.e. W/W, W/V, V/V.
    1. Weight per unit weight (W/W)
      A 10% W/W solution contains 10 gm of solute in 90 gm of solvent.
    2. Weight per unit volume (W/V)
      A 10% W/V solution contains 10 gm of solute dissolved in final volume of 100 ml of solution
    3. A 10% V/V solution contains 10 ml of the concentrate per 100 ml of solution.
  2. Molarity
    A molar solution contains 1 gm mol. wt. (mole) of solute in one litre of solution. Molarity of solution is expressed as ‘M’
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    For example:
    Molarity of a solution of 2 litres containing 58.5 gm. NaCl dissolved.
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    2
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    So, Molarity of given solution is 0.5 M.
  3. Normality
    A normal solution contains 1 gm equivalent Wt. (eq.) of solute dissolved in one litre of solution. Normality of solution is expressed as ‘N’
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    To evaluate equivalents of solute, we divide the molecular weight by its total valency of cation or anion.
    Eg. equivalent weight:
    1. of NaCl = Mol. wt. of NaCl
    For example:
    Normality of a solution of 2 litres containing 180 gm of glucose.
    • Equivalents of glucose will be same as its moles because it does not dissosiate in solution.
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    So, Normality of given solution is 0.5 N.
  4. Molality
    Molality is defined as number of moles of solute dissolved in 1000 gm of solvent (Not in solution).
    It is designated as ‘M’.
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    3
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    Unlike normality and molarity, this parameter of expressing the concentration is independent of temperature as there is no volume term in this relation.
  5. Formality
    Formality parameter is not used nowadays because all of the above parameters are better than it and are able to express concentration sufficently.
    Formality is same as molarity if molecular weight in the formula is replaced by formula weight.