Notes on Pure Substances and Mixtures

Pure Substances and Mixtures

Particle Theory

  • Everything is made of particles.
  • There are spaces between the particles.
  • Particles are attracted to each other.
  • Temperature affects the speed at which particles move:
    • Higher temperature = faster particle movement.
  • Particles are always moving because they have kinetic energy.
  • Different kinds of particles exist, but all particles of one substance are identical.

How Particles React Depending on Their State

  • Solid:

    • Particles in solids are tightly held together.
    • Strong attraction between particles.

  • Liquid:

    • Particles in liquids are fairly close but with some attraction.
    • They can move in all directions but not far.

  • Gas:

    • Particles in gases have very little attraction.
    • They move rapidly in all directions and collide with the container walls.

Atoms and Molecules

  • Atom:

    • The smallest particles that cannot be divided further.
    • Building blocks of matter.

  • Molecule:

    • A group of atoms bonded together.

  • Compound:

    • Two or more different elements bonded together (e.g., water = hydrogen + oxygen).

Pure Substances and Mixtures

  • Pure Substance:

    • Made of one element or compound (e.g., water).

  • Mixture:

    • Made of more than one element or compound (e.g., water + sugar).
    • Contains no chemical reactions between particles.
    • Proportions vary and can be separated physically.

Types of Mixtures

  • Homogeneous Mixture:

    • Looks uniform throughout (e.g., apple juice).

  • Heterogeneous Mixture:

    • Contains visibly different substances (e.g., ice in soda, soil, cereal in milk).

  • Mechanical Mixtures:

    • Components maintain original identities and are combined physically (e.g., salad, oil, and vinegar dressing).

Solutions

  • Definition:

    • A homogeneous mixture of solute and solvent.

  • Solvent:

    • Substance that dissolves another (e.g., water).

  • Solute:

    • Substance being dissolved (e.g., salt in saltwater).

  • Water:

    • Known as universal solvent due to its ability to dissolve many substances.

Solubility

  • Describes how well a solute dissolves in a solvent.

  • Factors affecting solubility:

    1. Concentration
    2. Temperature
    3. Pressure
    4. Size of solute particles

  • Concentration:

    • Amount of solute compared to solvent.
    • More solute leads to higher concentration but less solubility eventually.

  • Temperature:

    • Higher temperature increases solubility for solids but decreases for gases.

  • Size of Solute Particles:

    • Smaller particles dissolve faster (e.g., powdered sugar vs. sugar cube).

Mixture Classifications

  • Suspensions:

    • Mixture of liquid and solid particles (e.g., sand and water). Solid settles over time.

  • Colloids:

    • Small particles evenly distributed, do not settle (e.g., milk, smoke).

  • Emulsions:

    • Mixture of two immiscible liquids such as oil and water.

Environmental Impact of Pure Substances

  • Mining for pure substances (like gold) can harm the environment:
    • Disturbances cause pollutants to spread into water systems.
  • Refining:
    • Process to purify raw materials (e.g., refining gold with acids).

Questions for Review

  1. Define solution, solute, and solvent.
  2. Identify solute and solvent in a saltwater solution.
  3. For the following, identify if they are a solvent, solute, or solution:
    • Chocolate powder in hot chocolate
    • Saltwater
    • Carbon dioxide in soda
    • Sugar in tea
    • Water in coffee
    • Lemonade
    • Air
  4. Why is water considered the universal solvent?
  5. Why does salt dissolve in water?
  6. Explain strong vs. weak concentration.
  7. Define dissolve and dilute.

Conclusion

  • Understanding the differences between pure substances and mixtures: their properties, how they interact, and their environmental impacts is crucial in science.