Summary of "Molarity, Molality, Volume & Mass Percent, Mole Fraction & Density - Solution Concentration Problems"

Summary of Video:

"Molarity, Molality, Volume & Mass Percent, Mole Fraction & Density - Solution Concentration Problems"

Solution Components:
- Solute: Substance being dissolved (e.g., Sodium Chloride).
- Solvent: Substance doing the dissolving (e.g., water).
- Solution: Solute + Solvent combined.
Concentration Units and Formulas:
- Mass Percent (%) Mass % = (mass of solute / mass of solution) × 100
- Volume Percent (v/v %) Volume % = (volume of solute / volume of solution) × 100
- Mole Fraction (X): For substance A in a mixture: XA = moles of A / total moles in solution
- Molarity (M): M = moles of solute / liters of solution Volume must be in liters.
- Molality (m): m = moles of solute / kilograms of solvent Note: Molality uses mass of solvent, not solution.
- Density (ρ): ρ = mass / volume Common units: g/mL or g/cm³ (1 mL = 1 cm³). Useful conversions:
  - 1 L = 1000 mL
  - 1 kg = 1000 g

Molarity vs Molality: Molarity depends on volume of entire solution (solute + solvent). Molality depends on mass of solvent only.
Solute vs Solvent in Mixed Solvent Systems: If both substances can act as solvents (e.g., Methanol and water), the solute is usually the component in lesser quantity or as specified by the problem.

Identify solute and solvent.
Use the correct formula based on the concentration unit asked.
Convert units as necessary:
- Grams to moles (using molar mass).
- Milliliters to liters (for Molarity).
- Grams to kilograms (for Molality).
Calculate total mass or volume of solution if not given (solute + solvent).
Use Density to convert between mass and volume if needed.
Plug values into formulas and solve.

Mass Percent of NaCl: Given 15 g NaCl + 225 g water → total solution = 240 g. Mass % NaCl = (15/240) × 100 = 6.25%.
Volume Percent of Methanol and Mass Percent of Water: Methanol volume = 25 mL, Water volume = 150 mL → solution volume = 175 mL. Volume % Methanol = (25/175) × 100 = 14%. Use Density to find mass: - Methanol mass = 25 mL × 0.792 g/mL = 19.8 g - Water mass = 150 mL × 1 g/mL = 150 g Total mass = 169.8 g Mass % water = (150/169.8) × 100 = 88.3%.
Mole Fraction of KCl: 2 moles KCl + 8 moles water → total moles = 10. Mole Fraction KCl = 2/10 = 0.2.
Mole Fraction of NaF: Convert 25 g NaF to moles: - Molar mass NaF ≈ 42 g/mol → 25/42 = 0.595 moles. Convert 200 g water to moles: - Molar mass H₂O ≈ 18 g/mol → 200/18 = 11.1 moles. Mole Fraction NaF = 0.595 / (0.595 + 11.1) ≈ 0.