💏Intro to Chemistry Unit 11 – Solutions and Colloids

What's the Big Deal?

• Solutions and colloids are everywhere in our daily lives (soda, air, blood, milk)
• Understanding solutions and colloids is crucial for many fields (chemistry, biology, medicine, engineering)
  • Helps develop new technologies (drug delivery systems, water purification, advanced materials)
• Solubility plays a key role in chemical reactions and processes (extraction, purification, synthesis)
• Concentration of solutions determines their properties and applications (pH, osmotic pressure, reactivity)
• Colloidal systems have unique characteristics that differ from true solutions (Tyndall effect, stability, surface properties)
• Mastering solution calculations is essential for preparing accurate and precise solutions in labs and industries

Key Concepts

• Solute: the substance that dissolves in a solvent to form a solution
• Solvent: the substance in which a solute dissolves to form a solution (usually present in larger amount)
• Solubility: the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature
• Concentration: the amount of solute present in a given amount of solution (expressed in various units)
• Colligative properties: properties of solutions that depend on the concentration of solute particles (freezing point depression, boiling point elevation, osmotic pressure)
• Tyndall effect: the scattering of light by colloidal particles, making the beam of light visible (distinguishes colloids from true solutions)
• Brownian motion: the random motion of colloidal particles caused by collisions with solvent molecules

Types of Solutions

• Solid solutions: solute and solvent are both solids (alloys, gemstones)
• Liquid solutions: solute is dissolved in a liquid solvent (salt water, sugar water, alcoholic beverages)
  • Aqueous solutions: solutions where water is the solvent
  • Non-aqueous solutions: solutions where the solvent is not water (ethanol, acetone)
• Gaseous solutions: solute and solvent are both gases (air, natural gas)
• Unsaturated solutions: contain less solute than the maximum amount that can dissolve at a given temperature
• Saturated solutions: contain the maximum amount of solute that can dissolve at a given temperature
• Supersaturated solutions: contain more solute than the maximum amount that can dissolve at a given temperature (metastable, prone to crystallization)

Solubility and Factors Affecting It

• Temperature: generally, solubility of solids in liquids increases with increasing temperature (exceptions exist)
  • Solubility of gases in liquids decreases with increasing temperature
• Pressure: solubility of gases in liquids increases with increasing pressure (Henry's law)
  • Pressure has little effect on the solubility of solids and liquids
• Nature of solute and solvent: "like dissolves like" principle (polar solutes dissolve in polar solvents, non-polar solutes dissolve in non-polar solvents)
• Molecular size: smaller molecules tend to have higher solubility than larger molecules
• pH: solubility of some compounds depends on the pH of the solution (solubility of bases increases in acidic solutions, solubility of acids increases in basic solutions)
• Presence of other substances: common ion effect (presence of a common ion reduces solubility), salting out (addition of a salt decreases solubility of another compound)

Colloidal Systems

• Colloids: heterogeneous mixtures with particle sizes between 1 nm and 1000 nm (larger than molecules but smaller than particles visible to the naked eye)
  • Dispersed phase: the substance present as small particles in a colloid
  • Dispersion medium: the continuous phase in which the dispersed phase is suspended
• Types of colloids: aerosols (liquid droplets or solid particles in gas), foams (gas bubbles in liquid or solid), emulsions (liquid droplets in another liquid), sols (solid particles in liquid), gels (solid network with liquid dispersed throughout)
• Stability of colloids: maintained by electrostatic repulsion (particles with the same charge repel each other) and steric stabilization (adsorbed molecules on particle surfaces prevent aggregation)
• Coagulation and flocculation: processes by which colloidal particles aggregate and settle out of the dispersion medium (induced by adding electrolytes or changing pH)
• Applications of colloids: food products (milk, mayonnaise, whipped cream), cosmetics (lotions, creams), medicines (ointments, intravenous fluids), paints, inks, and coatings

Concentration and Calculations

• Mass percentage (% w/w): mass of solute divided by mass of solution, multiplied by 100
• Volume percentage (% v/v): volume of solute divided by volume of solution, multiplied by 100
• Mass-volume percentage (% w/v): mass of solute (in grams) divided by volume of solution (in milliliters), multiplied by 100
• Parts per million (ppm) and parts per billion (ppb): mass of solute per million or billion parts of solution
• Molarity (M): moles of solute per liter of solution
  • Calculating molarity: $molarity = \frac{moles \space of \space solute}{volume \space of \space solution \space (L)}$
• Molality (m): moles of solute per kilogram of solvent
  • Calculating molality: $molality = \frac{moles \space of \space solute}{mass \space of \space solvent \space (kg)}$
• Dilution: process of adding more solvent to a solution to decrease its concentration
  • Dilution formula: $M_1V_1 = M_2V_2$ (initial molarity × initial volume = final molarity × final volume)

Real-World Applications

• Water treatment: removing impurities and contaminants from water using solubility principles (precipitation, adsorption, ion exchange)
• Pharmaceuticals: preparing drugs in various forms (solutions, suspensions, emulsions) for optimal delivery and bioavailability
• Environmental chemistry: understanding the fate and transport of pollutants in water, soil, and air based on their solubility and colloidal properties
• Food science: creating stable and appealing food products by controlling the solubility and colloidal properties of ingredients (emulsifiers, stabilizers, thickeners)
• Materials science: designing advanced materials with desired properties by manipulating the solubility and colloidal structure (nanocomposites, self-assembled structures)
• Analytical chemistry: using solubility and colloidal properties for separation and purification techniques (extraction, chromatography, electrophoresis)

Lab Experiments and Demos

• Preparing solutions of different concentrations and observing their properties (color, density, viscosity)
• Demonstrating the Tyndall effect using a laser pointer and various solutions and colloids (milk, starch solution, smoke)
• Investigating factors affecting solubility by measuring the solubility of a solute at different temperatures or in different solvents
• Observing the effect of electrolytes on the stability of colloids (adding salt to a colloidal dispersion and observing flocculation)
• Extracting a solute from a solution using solubility differences (extracting iodine from an aqueous solution using mineral oil)
• Preparing a supersaturated solution and inducing crystallization by adding a seed crystal or disturbing the solution
• Demonstrating osmosis using a semi-permeable membrane and solutions of different concentrations (sucrose solution and water separated by a dialysis membrane)
• Conducting a titration experiment to determine the concentration of an unknown solution using a standard solution of known concentration