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Composition of Mixtures

Ethan Taylor

Ethan Taylor

7 min read

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Study Guide Overview

This study guide covers the classification of matter by composition, focusing on mixtures. It explains pure substances vs. mixtures, homogeneous vs. heterogeneous mixtures, and separation techniques like distillation, filtration, and thin-layer chromatography (TLC). The guide also includes practice questions and key concepts for the AP Chemistry exam, emphasizing polarity and its role in separation.

AP Chemistry: Mixtures and Separation Techniques 🧪

Welcome to your ultimate guide for mastering mixtures and separation techniques! This guide is designed to help you feel confident and fully prepared for your AP Chemistry exam. Let's dive in!

Classification of Matter by Composition

Remember, matter can be categorized by its state (solid, liquid, gas) or its composition. We're focusing on composition here. The first key division is between pure substances and mixtures.

  • Pure Substance: Composed of a single type of atom or molecule. Think of elements like gold (Au) or compounds like water (Hâ‚‚O).
  • Mixture: Composed of two or more elements or compounds physically combined. The key word here is physically.

What are Mixtures?

Mixtures are materials made up of two or more substances that are physically combined. They don't form chemical bonds with each other.

Formula Units: Pure Substances vs. Mixtures

  • Pure Substances: Contain atoms or formula units of a single type. For example, pure water (Hâ‚‚O) contains only Hâ‚‚O molecules.
  • Mixtures: Contain atoms or formula units of two or more types. The proportions of these components can vary. For example, salt water contains both Hâ‚‚O and NaCl.

Types of Mixtures

Mixtures are divided into two categories: homogeneous and heterogeneous.

  • Homogeneous Mixtures: Uniform in composition. You can't see the individual components.
Key Concept
  • Examples: Salt water (Hâ‚‚O + NaCl), air (Nâ‚‚, Oâ‚‚, etc.)
    • Difficult to separate, as components are evenly dispersed.
  • Heterogeneous Mixtures: Non-uniform composition. You can see the different components.
    • Examples: Rocky road ice cream (ice cream, nuts, marshmallows), salad (lettuce, tomatoes, etc.)
    • Often easily separable, as components are physically distinct.

Question 1 of 11

Which of the following is considered a pure substance? ✨

Salt water

Air

Gold (Au)

Rocky road ice cream