Molal solution:
Molal solution of any substance can be defined as
one mole of that substance or solute dissolved per kg of solvent. One molal
solution can be defined as gram equivalent weight (one mole) of a given
substance dissolved per kilograms of solvent. Molality of a solution is not
dependent upon the reaction temperature.
Molality:
Molal solution is prepared by dissolving one mole of
specified mass of solute per 100 grams of the given solvent. Molality of a
given solution can be calculated using following equation (1) if the mass of
the solute is given.
If the amount of solvent is not given and only mass
of solute is given the solution is prepared per kg of the given solvent and
given mass of solute is simply multiplied by molar mass of that solute. In case
the amount of solvent is given in grams then the amount in grams is first
converted into kilograms by dividing this value with 1000.
As,
1 kg = 1000 g
Equation 1 can be modified as number of moles of a
substance is equal to the given mass of substance divided by the molar mass of
that substance. Thus, equation 1 can be written as
Amount of solvent taken to prepare one molal
solution of any substance is quite different from one molar solution of using
same solvent. The difference is due to the way we weigh the solvent while
making molal solution and measure the solvent for molar solutions.
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