2.4 Chemistry of Commercial Products: Mixtures - Study Notes

Introduction

• Mixtures are encountered daily (e.g., powdered juice drinks, coffee).

• Commercial products exploit differences in physical and chemical properties of mixture components.

• Focus of the lesson: identify common homogeneous and heterogeneous mixtures in commercial products and compare them by use, safety, quality, and cost.

Key Concepts

• Mixture vs. pure substance vs. compound

  • A compound is a pure substance with atoms chemically bonded in fixed ratios; components cannot be separated by physical means.

  • A mixture is two or more pure substances physically combined, each retaining its own identity and properties.

• Homogeneous vs. heterogeneous mixtures

  • Homogeneous mixtures (solutions): uniform composition and properties; appear as one phase; components cannot be distinguished by the naked eye.

  • Heterogeneous mixtures: non-uniform composition; two or more phases; components can be visually distinguished.

• Subtypes of heterogeneous mixtures

  • Suspensions: solute particles do not dissolve; may settle into layers (layered upon standing).

  • Colloids: solute-like particles dispersed in a medium; do not readily separate into layers; particles are larger than in solutions but too small to settle quickly.

• Definitions and distinctions

  • Solvent: the component in greater amount that dissolves the solute (dispersing medium in a solution).

  • Solute: the component present in lesser amount that is dissolved.

  • In mixtures, components retain their own identities and properties; in compounds, elements are chemically combined in fixed ratios.

• Separation principles

  • Because each substance has characteristic properties, physical methods can separate components of mixtures (e.g., filtration, distillation, sedimentation, centrifugation).

• Particle scale and tests

  • Solutions: smallest particles; indistinguishable; single phase.

  • Colloids: dispersed phase particles are larger than in solutions; exhibit Brownian motion and the Tyndall effect.

  • Suspensions: larger particles; may settle over time, forming layers.

Common Homogeneous Mixtures in Commercial Products

• Homogeneous mixtures (solutions) have two components: solvent and solute; uniform distribution; one phase.

• Examples prepared routinely as solutions:

  • Vinegar: liquid solution of acetic acid in water.

  • Acetic acid concentration: $4\\%$ (by typical market formulation).

  • Legal minimum: vinegar must contain at least $4 \\text{g}$ of acetic acid per $100 \\text{mL}$ of water.

  • Fish sauce (patis): liquid solution in salt; a salted fish/krill fermentation product.

  • Sodium content mentioned: $7.851 \\text{g}$ of sodium per $100 \\text{g}$ of fish sauce.

  • Soft drinks, fruit juices, and alcoholic beverages:

  • Sugars dissolved in water; flavorings and coloring added.

  • Soft drinks often show CO₂ gas coming out when poured, indicating a transition from a primarily homogeneous solution to a heterogeneous state upon gas release.

  • Alcoholic beverages (ethanol in water):

  • Beer: $4.5\\%$ ethanol (approx. 4.5 mL ethanol per 100 mL).

  • Wine: $11.6\%$ ethanol (approx. 11.6 mL ethanol per 100 mL).

  • Liquor: $37\%$ ethanol (approx. 37 mL ethanol per 100 mL).

  • Rubbing alcohol: typically a $70\%$ solution of ethanol or isopropyl alcohol in water.

  • Rationale: high flammability and effectiveness as antiseptic.

  • Intravenous (IV) glucose solutions (dextrose in water):

  • Common concentrations: $5\%$ to $10\%$ dextrose in water.

  • Used to replenish fluids and provide carbohydrates.

  • Recall: homogeneous mixtures or solutions have components that are indistinguishable and appear in a single phase.

Common Heterogeneous Mixtures in Commercial Products

• Heterogeneous mixtures have non-uniform composition and appearance; they may consist of two or more phases.

• Subtypes: suspensions and colloids.

  • Suspensions: solute particles do not dissolve; particles may form clumps or layers and settle upon standing.

  • Colloids: dispersed phase particles are suspended in a medium; do not readily separate; Brownian motion and the Tyndall effect are common.

• Everyday examples:

  • Suspensions: iced tea with visible ice; coffee with undissolved milk solids initially; certain condiments like ketchup and mustard (often categorized as suspensions when components separate over time).

  • Colloids: milk (emulsion of fat droplets in water); mayonnaise (emulsion of oil in water with emulsifiers); milk and some dressings can behave as colloids.

  • Soups and mixtures of various ingredients are typically heterogeneous and can be either suspensions or colloids depending on composition and phase distribution.

• Condiments and emulsions

  • Mayonnaise: a colloidal emulsion (oil droplets dispersed in an aqueous acetic acid solution) with emulsifying agents (e.g., egg yolk).

  • Ketchup and mustard: suspensions in water-based matrices; if allowed to stand, solids may separate from the liquid phase.

  • Mayonnaise vs. other emulsions: emulsions are colloids where the dispersed phase (oil) is dispersed in the continuous phase (aqueous acidic solution).

• Colloid types and characteristics

  • Colloids are classified by the phase of the dispersing medium:

  • Gaseous colloids: the dispersing medium is gas (e.g., aerosol).

  • Liquid colloids: the dispersing medium is liquid (e.g., emulsions, sols, foams).

  • Solid colloids: the dispersing medium is solid (e.g., gels, solid sols).

  • Dispersed phase can be solid, liquid, or gas; examples include:

  • Aerosols: solid or liquid dispersed in a gas (e.g., cigarette smoke – solid in air; perfume sprays – liquid in air).

  • Emulsions: liquid dispersed in another liquid (oil droplets in water; e.g., milk).

  • Sols: solid dispersed in a liquid (ink – solid pigments in liquid).

  • Foams: gas dispersed in a liquid (shaving foam).

  • Gels: solid dispersed in a liquid (gel-like networks such as gelatin).

  • Solid sols: solids dispersed in a solid medium (e.g., colored glass).

• Tyndall effect and Brownian motion

  • Colloidal particles scatter light (Tyndall effect); Brownian motion is the random movement of colloidal particles in a fluid.

  • A simple demonstration: shining a beam of light through a colloidal mixture makes the path visible due to scattering.

• Summary table concepts (types of colloids)

  • Gas dispersing medium with solid dispersed phase: solid aerosol (e.g., cigarette smoke) in air.

  • Gas dispersing medium with liquid dispersed phase: liquid aerosol (e.g., perfume sprays) in air.

  • Liquid dispersing medium with dispersed phase (oil in water): emulsion (e.g., mayonnaise).

  • Liquid dispersing medium with dispersed phase: sol (ink or similar pigments in liquid).

  • Liquid dispersing medium with dispersed phase: foam (gas in liquid; shaving foam).

  • Solid dispersing medium with dispersed solid: solid sol (colored glass).

  • Solid dispersing medium with dispersed solid: gel (gel network in a liquid).

Applications of Separation Methods in Commercial Products

• Principle: each component has characteristic properties that can be exploited to separate components.

• Separation techniques used in industry and daily life include:

  • Distillation: separates components of mixtures based on differences in boiling points; widely used in refining petroleum to produce gasoline, kerosene, and other products.

  • Filtration: removes particulates from liquids or gases.

  • Sedimentation: letting heavier particles settle out of a mixture.

  • Centrifugation: uses rapid rotation to separate components by density; e.g., blood components.

  • Activated carbon adsorption: removes impurities and odors from water and other liquids.

  • Microfiltration: removes small particles from water or solutions.

• Industry-specific examples:

  • Petroleum industry: crude oil is a complex mixture; distillation produces gasoline, kerosene, and other products.

  • Water treatment: tap water is a heterogeneous mixture with particulates; treatment removes particulates, odor, color, and some bacteria; common separation methods include filtration, sedimentation, and activated carbon adsorption.

  • Health/medical: centrifugation used to separate blood components or urine for analysis; many biological fluids are colloidal in nature.

• Practical note: separation techniques are essential for achieving purity, safety, and quality in consumer products and industrial processes.

Real-World Examples and Visual Metaphors

• Everyday solutions (homogeneous) include coffee, vinegar, fruit juices, soft drinks, and IV dextrose solutions.

• Everyday heterogeneous products include suspensions (ice in drinks) and emulsions (milk, mayonnaise).

• Emulsions require emulsifying agents (e.g., egg yolk in mayonnaise) to keep droplets dispersed and prevent separation.

• When a product separates over time (e.g., ketchup sediment forming), this is a sign of a suspension or non-stable colloid.