Difference between Strength and Mole fraction

Difference between Strength and Mole fraction

Expressing the Concentration of a Solution:

          The amount of solute present in a given quantity of solution or dissolved in a given amount of solvent is called the concentration of a solution. Depending on the units of the solute and solvents taken, the concentrations of a solution can be expressed in many ways.

Strength (s): It is defined as the amount of solute in gram dissolved per litre of solution.

S = (weight of solute in gram/ volume of solution in ml) X 1000.

For example if 4gm urea is dissolved in 500 ml then strength of the solution,

s = (4/500) x 1000 = 8 g/ltr

Mole fraction (X): Mole fraction of a component in a solution is defined as the ratio of moles of that component to the total number of moles of all the components present in the solution. In a binary solution, if n₁ is the numbers of moles of solvent and n₂ is the numbers of moles of solute then,

      X _solvent = n₁ / (n₁ + n₂)                 and                      X _solute = n₂ / (n₁ + n₂)

Note 1: Sum total of mole fractions of all the components of a solution is equal to one. Ex:  X₁ + X₂ = 1 (for a binary solution).

Note 2: The number moles of a component (n) α mole fraction of that component (x). Hence, n₁ / n₂ = x₁ / x₂ , 1 and 2 represent component 1 and 2.

Relationship between mole fraction and molarity:

M = (1000 . density . W . X₂) / (w + W) . M₁ . X₁,

M = (1000 . density . X₂) / ( M₁ . X₁ + M₂ . X₂)

X₂  = MM₁ / {M(M₁- M₂) + density} where, W and w = weight of solvent and solute respectively, M₁ and M₂ are the molecular mass of solvent and solute respectively, X₁ and X₂  are the mole fractions of solvent and solute respectively.

Relationship between mole fraction and molality:

m = 1000 . X₂ / X₁ . M, where M is the molecular mass of solvent, X₁ and X₂ are the mole fractions of solvent and solute respectively.

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