Theory Exercises

Properties of Matter

Properties of matter are characteristics that can be observed or measured without changing the composition of the substance. Understanding these properties helps us classify and identify different materials.

Types of Properties

1. Physical Properties

Physical properties can be observed without changing the chemical composition of the substance.

Examples of Physical Properties:

  • Color: The visual appearance of a substance
  • Odor: The smell of a substance
  • Taste: How a substance tastes (only safe substances!)
  • Texture: How a substance feels to touch
  • Hardness: Resistance to scratching or deformation
  • Melting point: Temperature at which a solid becomes liquid
  • Boiling point: Temperature at which a liquid becomes gas
  • Density: Mass per unit volume
  • Solubility: Ability to dissolve in other substances
  • Conductivity: Ability to conduct heat or electricity

2. Chemical Properties

Chemical properties describe how a substance reacts with other substances or changes under certain conditions.

Examples of Chemical Properties:

  • Reactivity: How readily a substance undergoes chemical reactions
  • Flammability: Ability to burn in the presence of oxygen
  • Corrosion resistance: Ability to resist chemical breakdown
  • Acidity/Basicity: pH level of a substance
  • Oxidation: Tendency to lose electrons in reactions

Classification by Dependence on Amount

Extensive Properties

These properties depend on the amount of substance present.

  • Mass: Total amount of matter in an object
  • Volume: Amount of space occupied by matter
  • Length: Distance measurement
  • Energy: Total energy content

Intensive Properties

These properties do not depend on the amount of substance present.

  • Density: Mass per unit volume (ρ = m/V)
  • Temperature: Measure of average kinetic energy
  • Pressure: Force per unit area
  • Concentration: Amount of solute per unit of solution
  • Color: Visual appearance
  • Melting/Boiling points: Characteristic temperatures

Important Concepts

Density Formula

Density is one of the most important intensive properties. It's calculated using:

\[\rho = \frac{m}{V}\]

Where:

  • ρ (rho) = density
  • m = mass
  • V = volume

Example 1: Calculating density
Problem: A metal cube has a mass of 80 g and a volume of 10 cm³. What is its density? Solution:
\[\rho = \frac{m}{V} = \frac{80 \text{ g}}{10 \text{ cm}^3} = 8 \text{ g/cm}^3\]
Result: The density of the metal is 8 g/cm³.
Example 2: Finding mass from density
Problem: What is the mass of 25 cm³ of gold if gold has a density of 19.3 g/cm³? Solution: Rearrange the density formula to solve for mass:
\[m = \rho \times V = 19.3 \text{ g/cm}^3 \times 25 \text{ cm}^3 = 482.5 \text{ g}\]
Result: 25 cm³ of gold has a mass of 482.5 g.