Study Guides/Chemistry/Mole Fraction of Solute
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Mole Fraction of Solute

Mole fraction is a way to express the concentration of a solution. It is a dimensionless quantity used in Class 12 Chemistry (Solutions chapter).

Question (Click to Flip)

What is the mole fraction of solute in a very dilute solution?

Answer

In a very dilute solution, n(solute) << n(solvent), so mole fraction of solute approaches 0 and mole fraction of solvent approaches 1.

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Key Facts

Mole fraction is temperature-independent, unlike molarity which changes with temperature.

Definition and Formula

Mole fraction of solute is the ratio of the number of moles of solute to the total number of moles of all components in the solution.

ฯ‡(solute) = n(solute) / [n(solute) + n(solvent)]

Where:

  • ฯ‡ = mole fraction (chi)
  • n = number of moles

Key Properties

  • Mole fraction is always between 0 and 1.
  • Sum of mole fractions of all components = 1
    • ฯ‡(solute) + ฯ‡(solvent) = 1
  • It has no units (dimensionless).

Solved Example

If 2 moles of NaCl are dissolved in 8 moles of water:

  • ฯ‡(NaCl) = 2 / (2+8) = 2/10 = 0.2
  • ฯ‡(water) = 8 / (2+8) = 8/10 = 0.8
  • Check: 0.2 + 0.8 = 1 โœ“

Questions and Answers

What is the mole fraction of solute in a very dilute solution?+

In a very dilute solution, n(solute) << n(solvent), so mole fraction of solute approaches 0 and mole fraction of solvent approaches 1.

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