Question

When dealing with concentrations, there are three ways in which the amount of dissolved solute per unit volume are widely used in biological and chemical laboratories. What are the three methods of calculating concentrations based on volume?

Answer 1

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The three methods by which calculation of concentration takes place are as follows:-

1. Molarity (M)           2. Normality (N)            3. Weight to volume percent

1. Molarity(M) :- It is defined as the number of moles of the solute per liter of solution (or number of millimoles per ml. of solution).

Unit of molarity is mol/liter or mol/dm³.

For example, a molar 1 M solution of sugar means a solution containing 1 mole of sugar (i.e., 342 g) per liter of the solution. Mathematically molarity can be calculated by following formulas,

     ,

2. Normality (N) :- It is defined as the number of gram equivalents (equivalent weight in grams) of a solute present per litre of the solution. Unit of normality is gram equivalents litre^–1. Normality changes with temperature since it involves volume. When a solution is diluted x times, its normality also decreases by x times.

Mathematically normality can be calculated by following formulas,

3. weight to volume percentage :- It represent amount of solute in gram present in 100 ml of solution.

% w/v =

for example 10% w/v Na₂CO₃ solution means 10 gm of Na₂CO₃ is present in 100 ml of solution.