SCIENCE SUMMATIVE PRACTICE

1. Solutions and Saturation Levels

1.1 Core Terminology

• Solute: The substance that is dissolved (e.g., salt, sugar).

• Solvent: The liquid substance that dissolves the solute (e.g., water).

• Solution: A homogeneous mixture formed when a solute completely dissolves in a solvent.

1.2 Types of Solution Saturation

• Unsaturated Solution:

  • Contains less solute than the maximum limit that the solvent can dissolve at a specific temperature.

  • Additional solute can still dissolve if added to the solution.

• Saturated Solution:

  • Contains the maximum amount of dissolved solute possible at a given temperature.

  • Any extra solute added will not dissolve and remains at the bottom.

  • Represents a dynamic equilibrium where the rate of dissolution equals the rate of crystallization.

• Supersaturated Solution:

  • Contains more dissolved solute than a saturated solution at the same temperature.

  • Created by dissolving solute at a high temperature and slowly cooling the mixture without physical disturbance.

  • Highly unstable; adding a tiny seed crystal or stirring causes rapid precipitation/crystallization of the excess solute.

2. Solubility Curves

2.1 Graph Components

• Axes Structure:

  • $x$-axis: Temperature (measured in $^\bullet\text{C}$).

  • $y$-axis: Solubility (measured in $g\text{ solute}/100\,g\text{ of }H_2O$).

• Interpreting Points on the Graph:

  • On the curve line: Represents a saturated solution at that specific temperature.

  • Below the curve line: Represents an unsaturated solution.

  • Above the curve line: Represents a supersaturated solution (if fully dissolved) or a saturated solution with excess undissolved solid.

2.2 General Trends

• Solid Solutes: Solubility generally increases as temperature increases.

• Gaseous Solutes: Solubility decreases as temperature increases.

3. Eight Key Separation Techniques

3.1 Simple Distillation

• Purpose: Separates a liquid solvent from a non-volatile dissolved solid solute.

• Principle: Operates on large differences in boiling points between the components.

• Process: The mixture is heated; the solvent boils, turns to gas, and passes into a condenser where it cools back into pure liquid (distillate).

• Example: Obtaining pure liquid water from sea water.

3.2 Fractional Distillation

• Purpose: Separates two or more miscible liquids with close boiling points (typically less than $25\,^\circ\text{C}$ apart).

• Principle: Utilizes a fractionating column filled with glass beads to create repeated evaporation and condensation cycles.

• Process: Vapors rise up the column; the liquid with the lower boiling point vaporizes completely first and is collected.

• Example: Separating ethanol ($78\,^\circ\text{C}$) from water ($100\,^\circ\text{C}$).

3.3 Evaporation

• Purpose: Recovers a dissolved solid solute from a solution by evaporating the liquid solvent.

• Principle: The liquid component has a much lower boiling point than the solid component.

• Process: The solution is heated until the liquid turns into gas, leaving dry solid crystals behind.

• Example: Obtaining solid salt from a salt-water mixture.

3.4 Magnetic Separation

• Purpose: Separates magnetic substances from non-magnetic components in a solid mixture.

• Principle: Based on differing magnetic properties of substances.

• Process: A magnet is passed over the mixture, attracting magnetic particles while leaving non-magnetic materials behind.

• Example: Removing iron filings from sulfur powder or sand.

3.5 Centrifugation

• Purpose: Separates fine insoluble solids or fluids of differing densities suspended in a liquid.

• Principle: Uses rapid rotational force (centrifugal force) to push denser particles outward and downward.

• Process: Sample tubes spin at high speeds, forcing dense solids to form a pellet at the bottom while liquid remains on top.

• Example: Separating blood cells from blood plasma.

3.6 Sublimation

• Purpose: Separates a substance that sublimates from a non-sublimable solid in a mixture.

• Principle: One component transitions directly from a solid state to a gas state without becoming liquid.

• Process: Heat is applied to the mixture; the sublimable solid turns into vapor and recrystallizes on a cooled surface above.

• Example: Separating ammonium chloride ($\text{NH}_4\text{Cl}$) or iodine from sodium chloride ($\text{NaCl}$).

3.7 Filtration

• Purpose: Separates an insoluble solid from a liquid suspension.

• Principle: Relies on particle size differences relative to the pore size of a barrier.

• Process: The mixture passes through filter paper; solid particles (residue) are trapped, and liquid (filtrate) passes through.

• Example: Separating sand from water.

3.8 Paper Chromatography

• Purpose: Separates small amounts of dissolved substances (such as pigments or dyes).

• Principle: Based on differing solubilities in a mobile phase (solvent) and relative adsorption to a stationary phase (paper).

• Process: Solvent moves up chromatography paper, carrying components at different speeds according to solubility.

• Example: Separating individual colored dyes in black ink.

Simple Distillation = Big Boiling Difference. Use this when mixing two liquids that boil at completely different temperatures (at least 25°C apart), or separating a liquid from a dissolved solid (like salt water).

• Fractional Distillation = Close Boiling Difference. Use this when the liquids boil at temperatures very close to each other (like crude oil or alcohol and water). It uses a special column to separate them cleanly.

• Sublimation = Solid to Gas (Skip the Liquid). Use this when one of the solids can turn straight into a gas without melting first (like iodine, dry ice, or naphthalene/mothballs).