SOLUTIONS

Factors Affecting Solubility

  • Pressure (Primarily Relevant to Gases)

    • Increasing external pressure on a gas–liquid system forces more gas particles into the liquid phase.

    • Mechanistic view: higher pressure compresses the gas, increases collision frequency with the liquid surface, and drives dissolution.

    • Relationship is illustrated by an approximately linear curve (Henry‐type) in a typical “Solubility of a Gas vs. Pressure” graph.

    • Practical example

    • Carbonated beverages: \text{CO}_2 is bottled under high pressure so that large amounts remain dissolved; once opened (pressure released) excess gas escapes as fizz.

    • Real–world significance & implications

    • Beverage industry quality control; scuba diving (nitrogen narcosis risk when pressure changes); environmental engineering (dissolved oxygen levels in water bodies).

  • Temperature

    • Solids in Liquids

    • Raising temperature generally increases solubility.

      • Particle‐level rationale: higher thermal energy overcomes lattice forces in the solid and enhances molecular motion in the solvent.

    • Example: More sugar dissolves in hot tea than in iced tea.

    • Gases in Liquids

    • Raising temperature usually decreases solubility.

      • Warmer solvent molecules have greater kinetic energy, making it easier for dissolved gas molecules to escape to the gas phase.

    • Example: Soda loses its fizz faster when warm.

    • Broader connections

    • Aquatic life: warm water holds less dissolved oxygen, stressing fish.

    • Industrial design: cooling towers rely on this principle to strip dissolved gases.

Quantitative Expressions of Concentration (Percentage Based)

  • General Context

    • Percent formats communicate “how much solute” per “how much solution,” scaled to 100\%, enabling rapid comparison of mixture strengths in laboratory, medical, and industrial settings.

Percent by Mass (\% mass)

  • Formula (use when both solute and solution are weighed in grams):

    • \%\,\text{mass}=\frac{\text{mass of solute (g)}}{\text{mass of solution (g)}}\times100\%

  • Worked Example

    • 5\,\text{g} salt + 95\,\text{g} water \Rightarrow100\,\text{g} total solution.

    • \%\,\text{mass}=\frac{5\,\text{g}}{100\,\text{g}}\times100\%=5\% (Interpretation: 5\% of the solution’s mass is salt.)

  • Key takeaways / good practice

    • Always verify units match (g).

    • Common in solid–solid alloys, ointments, powdered food mixes.

Percent by Volume (\% volume)

  • Formula (use when solute and solution volumes are measured in milliliters):

    • \%\,\text{volume}=\frac{\text{volume of solute (mL)}}{\text{volume of solution (mL)}}\times100\%

  • Worked Example

    • 20\,\text{mL} alcohol + 80\,\text{mL} water \Rightarrow100\,\text{mL} total solution.

    • \%\,\text{volume}=\frac{20\,\text{mL}}{100\,\text{mL}}\times100\%=20\% (Interpretation: 20\% of the solution’s volume is alcohol.)

  • Usage notes

    • Predominant in liquid–liquid mixtures: antiseptics, perfumes, fuel blends (e.g., ethanol–gasoline mixtures).

Conceptual & Practical Cross-Links

  • Thermodynamic Principles

    • Solubility changes with temperature/pressure are underpinned by Le Chatelier’s Principle and the balance of enthalpy/entropy in dissolution processes.

  • Industrial & Environmental Ethics

    • Designing processes to minimize unwanted gas release (greenhouse gases) while maximizing product stability.

    • Understanding these variables helps mitigate ecological impact (e.g., thermal pollution lowering riverine oxygen).

  • Study Tips

    • Memorize the direction of solubility change: solids ↑ with T, gases ↑ with P but ↓ with T.

    • Re-derive the percentage formulas quickly in exams to avoid rote errors: “part over whole times 100\%.”

    • Draw quick sketches of solubility curves as visual aids.