Heterogeneous Mixtures

1.2b Classification of matter by its Chemical Composition

Mixtures (NOT Pure Substances)

Classify matter as a homogeneous mixture or heterogeneous mixture with regard to their physical state and composition

The science of macaroni salad: What's in a mixture?

What's in macaroni salad? Break down the pasta, mayonnaise, vinegar, mustard, vegetables, etc., and you're left with a bunch of molecules. Josh Kurz uses a delicious recipe to exemplify three types of mixtures (solution, colloid and suspension), while reminding us that we're all made of the same stuff.

Main Idea: Chapter 3-3 & 14-1

3-3: Most everyday matter occurs as mixtures — combinations of two or more substances.
14-1: Mixtures can be either heterogeneous or homogeneous.

Heterogeneous (mechanical) mixtures

A heterogeneous mixture is a mixture in which the composition is not uniform throughout the mixture.

Trail mix is a heterogeneous mixture. Any given handful of mix will contain varying amounts of the different components of the mixture.

A phase is any part of a sample that has a uniform composition and properties. By definition, a pure substance or a homogeneous mixture consists of a single phase. A heterogeneous mixture consists of two or more phases. When oil and water are combined, they do not mix evenly, but instead form two separate layers. Each of the layers is called a phase.

Suspensions

A suspension is a heterogeneous mixture of a fluid that contains solid particles sufficiently large for sedimentation.

The particles may be visible to the naked eye, usually must be larger than one micrometer, and will eventually settle, although the mixture is only classified as a suspension when and while the particles have not settled out.

A suspension is a heterogeneous mixture in which some of the particles settle out of the mixture upon standing.

The particles in a suspension are larger, so gravity is able to pull them down out of the dispersion medium (typically water).

Colloids

A colloid is a heterogeneous mixture in which the dispersed particles are much smaller that those of a suspension. The particles are spread evenly throughout the dispersion medium.

Because the dispersed particles of a colloid are not as large as those of a suspension, they do not settle out upon standing.

Types of Colloids

Tyndall effect

The Tyndall effect is the scattering of light as a light beam passes through a colloid where the individual suspended particles scatter and reflect light, making the beam visible.

Brownian motion

Brownian motion is the erratic random movement of microscopic particles in a fluid, as a result of continuous bombardment from molecules of the surrounding medium.

Blood separation

Types of Colloids

Key Concepts

A mixture is a physical blend of two or more pure substances in any proportion.
- The individual substances in a heterogeneous mixture remain distinct.
- Two types of heterogeneous mixtures are suspensions and colloids.
  - Brownian motion is the erratic movement of colloid particles.
  - Colloids exhibit the Tyndall effect.

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