22/05/2019
We can calculate the concentration of solutions by various methods. Let’s study each method and determine the formulas for this method.
1) Mass/Weight Percentage or Percentage by Mass/Weight
It is the amount of solute in grams present in 100 grams of the solution. Therefore, the formula will be:
The ratio mass of solute to the mass of the solvent is the mass fraction. Thus, the mass percentage of solute = Mass fraction × 100. 10% solution of sugar by mass means that 10 grams of sugar is present in 100 grams of the solution, i.e., we have dissolved 10 grams of sugar in 90 grams of water.
2) Volume Percentage
It is the volume of solute in mL present in 100 mL solution. The formula will be:
concentration of solutions
10% solution of HCl by volume means that 10 mL of liquid HCl is present in 100 mL of the solution.
3) Mass by Volume Percentage
It is the mass of solute present in 100 mL of solution. We can calculate the mass of the solute using the volume percentage.
A 10% mass by volume solution means that 10 gm solute is present in 100 mL of solution.
4) Molarity
The molarity of a solution gives the number of gram molecules of the solute present in one litre of the solution.
For example, 1 mol L-1 solution of KCl means that 1 mol of KCl is dissolved in 1 L of water. Unit of molarity: mol L-1
5) Molality
Molality of a solution is the number of moles of solute dissolved in 1 Kg of the solvent.
Thus, if one gram molecule of a solute is present in 1 kg of the solvent, the concentration of solutions is said to be one molal. The unit of molarity is mol kg-1. Molality is the most convenient method to express the concentration of solutions because it involves the mass of liquids rather than their volumes. It is also independent of the variation in temperature.
6) Normality
The normality of a solution gives the number of gram equivalents of the solute present in one litre of the solution.
Thus, if one gram equivalent of a solute is present in one litre of the solution, the concentration of solutions is said to be 1 normal.
1N = Normal = One gram equivalent of the solute per litre of solution = Normality is 1
