Pure Substances and Mixtures Flashcards

Pure Substances and Mixtures

• Pure Substance: Matter featuring a fixed composition and uniform properties throughout, consisting of only one particle type, and unable to be physically separated into other substances.
  • Element: Pure substance made of only one kind of atom. Examples: gold ($Au$), oxygen ($O_2$), iron ($Fe$).
  • Compound: Pure substance made of two or more elements chemically combined in a fixed ratio. Examples: water ($H_2O$), carbon dioxide ($CO_2$), table salt ($NaCl$).
• Mixture: Combination of two or more substances physically combined without chemical bonding.
  • Homogeneous Mixture: Displays a uniform composition throughout (e.g., saltwater, air).
  • Heterogeneous Mixture: Features non-uniform composition with visually distinct components (e.g., sand and water, oil and water, salad).

Scientific Method

• Definition: A systematic and organized process relying on observation, evidence, experimentation, and logical reasoning to investigate questions, solve problems, test ideas, and discover how things work.
• Sequential Steps:
  1. Ask Question / Identify the Problem: Formulate a clear inquiry ("Why") and construct a hypothesis.
  2. Prepare Needed Materials: Gather all necessary tools and equipment prior to conducting the experiment.
  3. Conduct Experimentation: Perform the experiment fairly by adhering carefully to procedure steps.
  4. Analyze Data: Collect, organize, and examine results using measurements, tables, or graphs to identify patterns.
  5. Draw Conclusion: Use results to answer the original question and state whether findings support the expected outcome.
  6. Communicate the Results: Share findings through reports, presentations, graphs, or posters to permit verification and replication.
• Hypothesis: An educated guess or testable proposed solution to a problem.

Laboratory Safety and Apparatus

• Safety & Emergency Protocols:
  • Laboratory rules ensure safety, prevent accidents, protect equipment, ensure proper experimentation, and maintain organization.
  • Emergency steps: stay calm, inform the teacher immediately, halt operations if safe, move away from hazards, avoid touching chemical spills or bare-hand handling of broken glass, and know the locations of first-aid kits and emergency exits.
• Apparatus Operational Procedure: Identify $\rightarrow$ Inspect $\rightarrow$ Use properly $\rightarrow$ Clean $\rightarrow$ Store. Report damaged equipment immediately.
• Apparatus Classifications:
  • Holding / Supporting: Test Tube Holder (Test Tube Clamp), Test Tube Rack (Test Tube Stand), Laboratory Tongs (Beaker Tongs), Rubber Thermometer Holder (Thermometer Clamp).
  • Containing: Test Tube (Reaction Tube), Beaker (Laboratory Beaker), Laboratory Vial (Sample Vial), Erlenmeyer Flask with Cork (Conical Flask), Reagent Bottle (Chemical Bottle), Round-Bottom Flask (Round Flask), Florence Flask (Boiling Flask).
  • Measuring: Graduated Cylinder (Measuring Cylinder), Laboratory Thermometer (Scientific Thermometer), Electronic Beam Balance (Electronic Balance).
  • Heating: Alcohol Lamp (Spirit Lamp), Hot Plate (Electric Hot Plate), Porcelain Crucible (Crucible Cup), Evaporating Dish (Evaporation Basin).
  • Transferring: Laboratory Dropper (Dropper Pipette), Funnel (Laboratory Funnel), Spatula (Laboratory Spatula).
  • Mixing and Grinding: Stirring Rod (Glass Stirring Rod), Mortar and Pestle (Grinding Bowl and Grinder).
  • Cleaning & Other: Test Tube Brush, Watch Glass (Watch Dish).

Historical Evolution of Atomic Models

• Democritus ($400\,\text{BC}$): First to use the term "atomos" (indivisible). Proposed that matter consists of solid, indivisible atoms lacking internal structure, separated by empty space, with variations in size, weight, and shape.
• John Dalton ($1800s$): Formulated the Billiard Ball Model (first modern atomic model). Described atoms as tiny, solid, indestructible, and unchangeable spheres of distinct atomic weights that combine chemically to form compounds.
• J.J. Thomson ($1890s$): Discovered negatively charged electrons. Created the Plum Pudding / Raisin Bread Model, picturing electrons embedded inside a sphere of positive charge.
• Ernest Rutherford ($1910s$): Conducted the Gold Foil Experiment with Johannes Wilhelm Geiger and Ernest Marsden by bombarding gold foil with positive alpha ($\alpha$) particles. Proposed the Nuclear Model, establishing a small, dense, positively charged nucleus holding most atomic mass, surrounded by orbiting electrons in mostly empty space.
• Niels Bohr ($1910s$): Developed the Planetary Model. Proposed that electrons move in fixed orbits (energy levels or shells); energy is lower closer to the nucleus, and electrons jump levels by gaining or losing energy.
• Erwin Schrödinger ($1920s$): Formulated the Quantum Mechanical Model (Electron Cloud Model). Discovered that electrons move within an electron cloud, where orbitals define regions of high probability for finding an electron rather than fixed paths.

Particle Model of Matter

• Core Principle: All matter is composed of microscopic particles (atoms, molecules, ions) in constant motion. Pure substances contain one type of particle, whereas mixtures contain distinct particle types.
• Particle Properties across States of Matter:
  • Kinetic Motion: Driven by Kinetic Energy. Solids vibrate in place; liquids move around each other; gases move freely and quickly.
  • Intermolecular Space: Spaces between particles are minimal in solids, moderate in liquids, and large in gases.
  • Intermolecular Forces of Attraction: Particle attraction is strong in solids, moderate in liquids, and weak in gases.
  • Thermal Response: Heat increases kinetic energy, causing particles to move faster. Heat/temperature and kinetic energy share a directly proportional relationship.