Concentration Terms and Solubility

topicmedium92 MCQ

Molarity, molality, mole fraction, ppm and Henry's law. (Chemistry › Solutions, NEET UG syllabus.)

What is Concentration Terms and Solubility?

The number of moles of solute dissolved per litre of solution.

Key formula / rule: Molarity (M)

Define and differentiate between various concentration terms: Molarity, Molality, Mole Fraction, Mass %, Volume %, and ppm.
Perform calculations involving these concentration terms.
Understand the effect of temperature and pressure on the solubility of solids and gases.
State and apply Henry's Law to calculate the solubility of gases in liquids.

Confusing solvent mass/volume with solution mass/volume.

Term: Mole Fraction
Meaning: The ratio of the number of moles of one component to the total number of moles of all components in the solution.

Term: Solubility
Meaning: The maximum amount of a solute that can dissolve in a given amount of solvent at a specific temperature and pressure to form a saturated solution.

Term: Henry's Law Constant (K_H)
Meaning: A proportionality constant in Henry's Law that relates the partial pressure of a gas above a solution to its mole fraction in the solution. Its value depends on the nature of the gas, solvent, and temperature.

Define and differentiate between various concentration terms: Molarity, Molality, Mole Fraction, Mass %, Volume %, and ppm.
Perform calculations involving these concentration terms.
Understand the effect of temperature and pressure on the solubility of solids and gases.
State and apply Henry's Law to calculate the solubility of gases in liquids.
Convert between different concentration units.

Name: Mole Fraction (χ)
Note: Unitless. Sum of mole fractions of all components is 1.
Expression: χ_solute = (moles of solute) / (total moles of solution) ; χ_solvent = (moles of solvent) / (total moles of solution)

Name: Parts per Million (ppm)
Note: Used for very dilute solutions.
Expression: ppm = (mass of solute / mass of solution) × 10⁶ (for mass-based) or (volume of solute / volume of solution) × 10⁶ (for volume-based)

Name: Henry's Law
Note: P is the partial pressure of the gas above the solution, K_H is Henry's Law constant, χ is the mole fraction of the gas in the solution.
Expression: P = K_H * χ

Confusing solvent mass/volume with solution mass/volume.
Incorrectly using units (e.g., grams instead of kg for molality, mL instead of L for molarity).
Not converting units properly (e.g., g to kg, mL to L).
Forgetting that Molarity is temperature-dependent while Molality is not.
Applying Henry's Law to gases that react with the solvent (e.g., NH3 in water).
Mixing up the definitions of mole fraction of solute vs. solvent.

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