Neelain University
Faculty of Medicine
Chemical Concentration and How it’s Expressed
Written by Abdulaziz Isam
What’s Chemical Concentration?
Definition
The concentration of a solution is a measure of the amount of solute that has been
dissolved in a given amount of solvent or solution. A concentrated solution is one that has a
relatively large amount of dissolved solute. A dilute solution is one that has a relatively small
amount of dissolved solute.
Concentration in everyday life
Concentration is often expressed in informal ways, use of adjectives such as “dilute” or
“concentrated” is common. Everyday practices such as adding more tea or sugar in order to
increase the amount of solute relative to the amount of solvent — to make the solution more
concentrated. As well as adding more solvents — such as water — to solutions in order to
make the solution more diluted, are commonplace.
Methods of Expressing Concentration
The following list contains a few methods used to express chemical concentration and how
to calculate them.
Molarity
Also known as Molar Concentration, is defined as the amount of solute in moles divided by
the volume of the solution
Unit: mol / L
Molality
Which is the amount of solute in moles divided by the mass of the solvent and not the entire
solution
Unit: mol / kg
Often due to thermal expansion, it is more convenient to use Molality instead of Molarity,
whose value is affected by temperature
Mole fraction
Is the amount of solute in moles divided by the amount of solution.
Unit: mol / mol. Often measured in Parts-Per-Notation
Mass fraction
It is the mass of the solute divided by the mass of the entire solution
Unit: kg / kg. Often measured in Parts-Per-Notation
Mass concentration
Which is defined the mass of a solute divided by the volume of the solution, for a pure
chemical this would equal its density (mass divided by volume)
Unit: kg / L
Uses of Concentration
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The concentration of a solute is very important in studying chemical reactions
because it determines how often molecules collide in solution and thus indirectly
determines the rates of reactions and the conditions at equilibrium
●
The concentration of a solution helps us to determine the collision speed between
particles in a molecule or compound.
●
This will in turn determine the rate of a particular reaction and the conditions in which
equilibrium can be maintained for the reaction.
●
The concentration of the solution also helps us to determine the solute and solvent
quantity.
●
Knowing the concentration of solutes is important in controlling the stoichiometry of
reactants for solution reactions.
References
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Infoplease
IUPAC compendium Gold Book
Chem.libretexts.org