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Ways Of Expressing Concentration

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Ways Of Expressing Concentration - Lesson Summary

The concentration of a solution is defined as the amount of solute dissolved in a given amount of solvent (or) solution. Concentration can be expressed qualitatively as well as quantitatively.

Qualitatively, a solution is expressed as either dilute or concentrated.

When a solution contains a small proportion of solute relative to the solvent it is a dilute solution. And a concentrated solution contains a large proportion of solute relative to the solvent.

Quantitatively the concentration of a solution can be described in several ways. These methods are:

  • Mass percentage
  • Volume percentage
  • Mass by volume percentage
  • Parts per million
  • Mole fraction
  • Molarity
  • Molality


The mass percentage of a component of a solution is defined as the mass of the component in the solution divided by the total mass of the solution multiplied by 100.

Mass % = (Mass of the component in the solution x 100)/ Total mass of the solution 

The volume percentage of a component in a solution is defined as the volume of the component divided by the total volume of the solution multiplied by 100.

Volume % = Volume of the component in the solution / Total volume of the solution x 100

Mass by volume percentage expressed as the mass of the solute divided by the total volume of the solution multiplied by 100.

Mass/Volume % = Mass of the solute/Total volume of the solution x 100

Parts per million (or) ppm is defined as the ratio of parts of the solute to million parts of the solution.

ppm = Total parts of the component / Total number of parts of all the components of the solution x 106

ppm → Mass to Mass (or) Volume to Volume (or) Mass to Volume


Molefraction:

The mole fraction of a component in a solution is defined as the ratio of the number of moles of that component to the total number of moles of all components in the solution. The mole fraction of the ith component (Xi) is expressed as,

 x = Number of moles of the component / Total number of moles of all components in the solution

If the solution contains i components

              Xi = ni /(n1+n2+n3+...+ni)


Molarity:

Molarity (M) is defined as the number of moles of a solute dissolved in one litre of the solution.

 M = Number of moles of the solute (n) / Total volume of the solution in litres (V)

        Mass of the solute = WB g
                 Molar mass  = MB g
        Volume of solution  = V mL

     M = WB / MB x 1000/V(mL)


Molality:
Molality (m) is defined as the number of moles of a solute dissolved per kilogram of the solvent.

m = Number of moles of the solute (n) / Mass of the solvent in kg

        Mass of the solute = WB g
        Mass of the solvent = WA g

m = WB / Molar mass of the solute x 1000/WA

Mass by mass percentage, parts per million, mole fraction and molality are independent of temperature, whereas molarity, volume by volume percentage and mass by volume percentage are functions of temperature.

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