Overview
This lecture covers the classification of matter into pure substances and mixtures, properties of elements, compounds, and mixtures, types of mixtures, solutions, and the Tyndall effect, including practical examples and key differences relevant for exams.
Classification of Matter
- Matter is anything that has mass and occupies space.
- Matter is classified as pure substances and mixtures.
- Pure substances are further divided into elements and compounds.
- Mixtures can be homogeneous (evenly mixed) or heterogeneous (unevenly mixed).
Pure Substances: Elements and Compounds
- Pure substances contain only one type of particle (atom or molecule).
- Elements are basic forms of matter that cannot be broken down by chemical reactions.
- Elements are classified as metals, nonmetals, and metalloids.
- Compounds are substances formed by chemically combining two or more elements in a fixed proportion.
- The properties of a compound differ from its constituent elements.
- Compounds can only be separated into elements by chemical means.
Mixtures
- Mixtures consist of two or more substances combined in any proportion, without chemical bonding.
- Mixtures can be separated by physical means (e.g., filtration).
- Homogeneous mixtures (solutions) have uniform composition; heterogeneous mixtures do not.
Types of Mixtures: Solution, Suspension, and Colloid
- True solutions have very small particles (< 1 nm) that do not scatter light.
- Suspensions have large particles (> 100 nm) that settle out and can be seen easily.
- Colloids have medium-sized particles (1–100 nm) and exhibit the Tyndall effect (scatter light).
- Components of colloids: Dispersed phase (like solute) and dispersing medium (like solvent).
Properties and Examples
- Solutions: E.g., sugar in water (homogeneous).
- Suspensions: E.g., soil in water (heterogeneous, particles settle).
- Colloids: E.g., milk in water (particles do not settle, scatter light).
Concentration and Solubility
- Concentration is the amount of solute present in a given amount of solution.
- Formulas:
- Mass % = (mass of solute / mass of solution) × 100
- Volume % = (volume of solute / volume of solution) × 100
- Solubility is the maximum amount of solute that can dissolve in a solvent at a specific temperature.
- Solubility increases with temperature for most solids.
Tyndall Effect and Light Scattering
- The Tyndall effect is the scattering of light by particles in colloids and some suspensions.
- True solutions do not show the Tyndall effect; colloids and suspensions do.
Physical and Chemical Changes
- Physical changes alter state, size, or shape without changing chemical identity (e.g., melting ice).
- Chemical changes result in formation of new substances (e.g., burning, rusting).
- Physical changes are often reversible; chemical changes usually are not.
Key Terms & Definitions
- Element — basic substance not broken by chemical means.
- Compound — substance chemically combined in fixed proportion.
- Mixture — combination of substances not chemically bonded.
- Homogeneous Mixture — mixture with uniform composition.
- Heterogeneous Mixture — mixture with visibly different parts.
- Solution — homogeneous mixture with tiny particles.
- Suspension — heterogeneous mixture with large, settleable particles.
- Colloid — mixture with dispersed particles, shows Tyndall effect.
- Solute — substance dissolved in a solution.
- Solvent — substance in which solute dissolves.
- Tyndall Effect — scattering of light by colloidal particles.
- Physical Change — change affecting form but not chemical identity.
- Chemical Change — change where new substances form.
Action Items / Next Steps
- Review and memorize differences between elements, compounds, and mixtures.
- Practice classifying examples as element, compound, or mixture.
- Solve numerical problems on concentration and solubility using given formulas.
- Try simple experiments to observe solutions, suspensions, colloids, and the Tyndall effect.
- Read the next chapter as assigned or indicated by your syllabus.