Pure Substances and Mixtures Quiz

Study Notes

Pure Substances and Mixtures

A pure substance has a constant composition and a fixed set of properties. Elements and compounds are pure substances.
Mixtures are combinations of two or more pure substances in which each substance retains its own properties. These components are not chemically bonded. Mixtures can be heterogeneous (uneven distribution) or homogeneous (uniform distribution).

Types of Mixtures

Heterogeneous mixtures: Components are visibly different and easily distinguishable. Examples include sand in water, oil and vinegar, and a salad.
Homogenous mixtures: Components are uniformly distributed and not easily distinguishable. Solutions are a type of homogeneous mixture.

Separation Techniques

Decantation: Separating a liquid from a solid by carefully pouring off the liquid. Useful for mixtures where the solid settles.
Filtration: Separating a solid from a liquid using a filter. Useful for mixtures where a solid is suspended in a liquid.
Evaporation: Separating a dissolved solid from a liquid by heating the mixture until the liquid evaporates, leaving the solid behind.
Distillation: Separating liquids with different boiling points. The liquid with the lower boiling point evaporates first and is collected, useful for mixtures of liquids.
Chromatography: Separating components of a mixture based on their different affinities for a stationary and mobile phase. Different molecules move at different speeds through the stationary phase.
Centrifugation: Separating components of a mixture with different densities by spinning the mixture at high speed. The heavier components settle at the bottom.
Magnetism: Separating magnetic substances from non-magnetic substances using a magnet.

Solutions

A solution is a homogeneous mixture of two or more substances.
The solute is the substance that is dissolved. The solvent is the substance that does the dissolving. "Like dissolves like" is a general principle for predicting solubility of one substance in another.
Concentration is a measure of the amount of solute dissolved in a given amount of solvent.
- Molarity (M): moles of solute per liter of solution.
- Mass percent: grams of solute per 100 grams of solution.
- Molality (m): moles of solute per kilogram of solvent.
Factors affecting solubility include temperature and pressure.
Unsaturated solutions can dissolve more solute.
Saturated solutions have dissolved the maximum amount of solute at a given temperature.
Supersaturated solutions contain more solute than a saturated solution, meaning that the solute is unstable and will precipitate out if conditions change.

Properties of Solutions

Colligative properties are properties of solutions that depend on the concentration of solute particles but not on the identity of the solute.
- Vapor pressure lowering: Dissolving a nonvolatile solute lowers the vapor pressure of the solvent.
- Boiling point elevation: The boiling point of a solution is higher than the boiling point of the pure solvent.
- Freezing point depression: The freezing point of a solution is lower than the freezing point of the pure solvent.
- Osmotic pressure: The pressure required to prevent the net flow of solvent across a semipermeable membrane. A semipermeable membrane allows certain molecules to pass through but not others.

Types of Solutions

Solid solutions: Also called alloys. Examples include brass (copper and zinc) and steel (iron and carbon).
Liquid solutions: A liquid solute dissolved in a liquid solvent or a liquid solute dissolved in a solid solvent.
Gaseous solutions: A gas dissolved in another gas. Air is a common example.

Description

Test your understanding of pure substances and mixtures with this quiz. Explore the characteristics of elements, compounds, and various types of mixtures, along with separation techniques like decantation and filtration. Perfect for students studying chemistry.