Question

What are the different ways of expressing the concentration of the solution?

Answer 1

Hint: Start this question by defining concentration and then its units. After this, write different methods for calculation of concentration of a solution and interconnect them.

Complete answer:

The Concentration of a Solution is defined as the relative amount of solute present in a solution.

Methods of Expressing Concentration of Solutions are as given below –

1. Percentage by weight

Symbol: (W / W %)

Definition: “It is the amount of solute present in 100 g of solution”.

Formula:  $ \text{weight percent (}\dfrac{\text{W}}{\text{W}}\text{) = }\dfrac{\text{weight of solute}}{\text{weight of solution}}\text{x100 }\!\!%\!\!\text{ } $ 

Unit: unitless

2. Percentage by volume

Symbol: (V / V %)

Definition: “It is defined as the volume of solute present in 100 mL of solution”.

Formula:  $ \text{volume percent (}\dfrac{\text{V}}{\text{V}}\text{) = }\dfrac{\text{volume of solute}}{\text{volume of solution}}\text{x100 }\!\!%\!\!\text{ } $ 

Unit: unitless

3. Weight by volume

Symbol: (W / V %)

Definition: “It is defined as the amount of solute present in 100 mL of solution”.

Formula:  $ \text{weight/volume percent (}\dfrac{\text{W}}{\text{V}}\text{) = }\dfrac{\text{weight of solute (g)}}{\text{volume of solution (L)}}\text{x100 }\!\!%\!\!\text{ } $ 

Unit: g/L

4. Mole fraction

Symbol:  $ \chi  $ 

Definition: “It is the ratio of the number of moles of solute and the total number of moles of solute and solvent”.

Formula:  $ {{\chi }_{\text{solute}}}=\dfrac{\text{moles of solute}}{\text{total moles of all components}} $ 

Unit: unitless

5. Parts per million

Symbol: ppm

Definition: “It is defined as the parts of a component per million parts ( $ \text{1}{{\text{0}}^{\text{6}}} $ ) of the solution. It is widely used when a solute is present in trace quantities”.

Formula:  $ \text{PPM=}\dfrac{\text{mass of solute}}{\text{mass of solution}}\text{x1}{{\text{0}}^{\text{6}}} $ 

Unit: ppm

6. Molarity

Symbol: M

Definition: “Molarity of any solution is the number of moles of solute per litre of solution”.

Formula:  $ \text{Molarity=}\dfrac{\text{moles of solute (mol)}}{\text{volume of solution (L)}} $ 

Unit: mol/L

7. Molality

Symbol: m

Definition: “Molality of any solution is represented as the number of moles of solute present per kg of solvent”.

Formula:  $ \text{Molality=}\dfrac{\text{moles of solute (mol)}}{\text{weight of solvent (kg)}} $ 

Unit: mol/kg

8. Normality

Symbol: N

Definition: “It is defined as the gram equivalent weight per litre of solution”.

Formula:  $ \text{Normality = }\dfrac{\text{mass of solute (g)}}{\text{equivalent mass x volume of solution (L)}} $ 

Unit: gram equivalent/ L.

Note: Concentration is basically a measure to find the amount of solute present in a solvent which together forms a solution.