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Some Basic Concepts Of Chemistry

Question
CBSEENCH11005096

Define molality and mole fraction.

Solution
Molality.  It is defined as the number of moles of the solute dissolved in 1kg (or 1000g) of the solvent.
Molality space equals fraction numerator Moles space of space solute over denominator Mass space of space solvent space in space kg end fraction
Mole fraction. Mole fraction may be defined as the ratio of the number of moles of one component to the total number of moles of all the components present in the solution.
For a binary solution made up of components A and B,
Mole space fraction space of space straight A left parenthesis straight x subscript straight A right parenthesis equals space space fraction numerator straight n subscript straight A over denominator straight n subscript straight A plus straight n subscript straight B end fraction
Mole space fraction space of space straight B left parenthesis straight x subscript straight B right parenthesis space equals fraction numerator straight n subscript straight B over denominator straight n subscript straight A plus straight n subscript straight B end fraction
Sum of the mole fractions open parentheses straight x subscript straight A plus straight x subscript straight B close parentheses
                           equals space fraction numerator straight n subscript straight A over denominator straight n subscript straight A plus straight n subscript straight B end fraction plus fraction numerator straight n subscript straight B over denominator straight n subscript straight A plus straight n subscript straight B end fraction space equals 1