Overview
This lecture introduces the concept of matter, how chemists classify different types of matter, and methods for separating mixtures, with practical examples and definitions.
What is Matter?
- Matter is anything that has mass and volume.
- Mass is measured in units like grams; volume in cubic meters or milliliters.
- Chemistry mainly deals with very small pieces of matter, such as atoms and molecules.
Classification of Matter
- Matter is classified as either pure substances or mixtures.
- Pure substances have a definite, unchanging composition.
- Mixtures have variable composition and are more common in real life.
Pure Substances
- Pure substances are either elements or compounds.
- Elements consist of only one kind of atom and cannot be split into simpler substances.
- Compounds are composed of two or more elements in a fixed chemical formula (e.g., H2O for water).
- The Law of Constant Composition states that a chemical compound always contains its components in the same ratio.
Mixtures
- Mixtures are physical blends of two or more substances with variable composition.
- Each part of a mixture retains its original properties.
- Examples include air (a mixture of gases) and lemonade (sugar, water, lemon juice in varying amounts).
Types of Mixtures
- Homogeneous mixtures have the same composition throughout (e.g., well-mixed paint, grocery store milk).
- Heterogeneous mixtures have visibly different components or phases (e.g., cereal in milk, fresh orange juice, trail mix, beach sand).
Separating Mixtures
- Mixtures can be separated based on physical properties.
- For example, salt can be separated from sand using water (dissolving, filtering, and evaporating).
Practice Classification Examples
- Helium: pure substance, element.
- Grocery store milk: mixture, homogeneous (homogenized).
- Glucose: pure substance, compound (C6H12O6).
- Gravity, sunbeam: not matter.
- Carbon dioxide: pure substance, compound (CO2).
- Trail mix: mixture, heterogeneous.
- Table salt: pure substance, compound (NaCl).
- Beach sand: mixture, heterogeneous.
Key Terms & Definitions
- Matter — anything with mass and volume.
- Element — pure substance of one type of atom, cannot be separated.
- Compound — pure substance of two or more elements in a fixed ratio.
- Mixture — blend of substances with variable composition.
- Homogeneous mixture — mixture with uniform composition.
- Heterogeneous mixture — mixture with visibly different parts.
- Law of Constant Composition — a compound always has the same ratio of elements.
Action Items / Next Steps
- Take a practice test on classifying matter to identify weak areas for study.
- Review physical and chemical properties of substances.
- Try separating a mixture (e.g., salt and sand) as a hands-on activity.