The mass percentage of a component in a given solution is the mass of the component per 100g of the solution. For e.g., if WA is the mass of the component A, WB is the mass of the component B in a solution. Then,
Example: A 10% solution of sodium chloride in water (by mass) means that 10g of sodium chloride are present in 100g of the solution.
This unit is used in case of a liquid dissolved in another liquid. The volume percentage is defined as the volume of the solute per 100 parts by volume of solution.For e.g., If VA is the volume of component A present is Vsol volume of the solution.
For e.g., a 10% solution of ethanol C2H5OH, in water (by volume) means that 10cm3 of ethanol is present in 100cm3 of the solution.
Strength of a solution is defined as the amount of the solute in gms, present in one litre of the solution. It is expressed as gL-1.
Molarity of a solution is defined as the number of moles of solute dissolved per litre of solution.Mathematically,
For e.g., If 'a' is the weight of the solute (in gms) present in VCC volume of the solution.
Molarity is expressed by the symbol M. It can also be expressed as,
Normality of a solution is defined as the number of gram equivalents (gm.e) of a solute dissolved per litre of the given solution.Mathematically it is,
For e.g., If a is the weight of the solute (in gms) present in VCC volume of the solution. Then,
Normality is expressed by the symbol N. It can also be expressed as,
Relationship between molarity and normality
The molarity and normality of a solution is related to each other as follows:
Molality of a solution is defined as the number of moles of solute dissolved in 1000g of a solvent. Mathematically, it is expressed as
Molality is expressed by the symbol m.Molality does not change with temperature.
In case of ionic compounds like KCl, CaCO3 etc. Formality is used in place of molarity.It is the number of gram formula masses of solute dissolved per liter of the solution. It is denoted by the symbol F. Mathematically it is given as,
It is the ratio of number of moles of one component (solute or solvent) to the total number of moles of all the components (solute and solvent) present in the solution. It is denoted by the symbol X. Let us suppose that a solution contains two components A and B and suppose that nA moles of A and nBmoles of B are present in the solution then,
Adding eq (i) and (ii) we get
xA + xB = 1
Parts per million (ppm)
When a solute is present in very small amounts, its concentration is expressed in parts per million. It is defined as the amount of the solute present in one million parts of the solution.
It may be noted that the concentration units like molarity, mole fraction etc. are preferred as they involve the weight of the solute and solvent, which is independent of temperature. But units like, molarity, Normality etc., involve volume of the solution, hence changes with temperature.