Untitled

1. Key Definitions

  • Matter: Anything that has mass and takes up space (has volume).

  • Chemistry: The study of matter, its properties, composition, structure, and the changes it undergoes.

  • Pure Substance: Matter that is composed of only one type of particle with a uniform and definite composition.

  • Mixture: Matter composed of two or more different pure substances physically combined.

  • Solution (Homogeneous Mixture): A mixture with a uniform appearance throughout, consisting of only one visible phase.

  • Mechanical Mixture (Heterogeneous Mixture): A mixture with two or more visible phases or parts.

  • Alloy: A solid solution composed of two or more metals, or a metal and a non-metal (e.g., brass, bronze, stainless steel).

  • Physical Property: A characteristic of a substance that can be observed or measured without changing its chemical identity.

  • Qualitative Property: A physical property described using words and senses (e.g., colour, texture, state, odour).

  • Quantitative Property: A physical property that can be measured and expressed using numerical values and units (e.g., mass, density, boiling point).

  • Physical Change: A change in which the substance alters its form, size, shape, or state, but retains its original chemical identity.

  • Chemical Property: A characteristic describing a substance's ability to react with other substances and form new substances (e.g., flammability, reactivity with acid).

  • Chemical Change: A change in which one or more new substances with different physical and chemical properties are formed.

  • Density: The ratio of a substance's mass to its volume, expressed as Density=MassVolume\text{Density} = \frac{\text{Mass}}{\text{Volume}}.

  • Boiling Point: The specific temperature at which a liquid changes state into a gas.

2. Classifying Matter: Solutions vs. Mechanical Mixtures

  • Solution:

    • Appears completely uniform throughout (single phase).

    • Individual components are evenly distributed and cannot be distinguished visually.

    • Examples: Salt dissolved in water, air, alloys like brass.

  • Mechanical Mixture:

    • Non-uniform appearance with distinct, visible parts or phases.

    • Components remain separate and visible to the naked eye or under magnification.

    • Examples: Oil and water, cereal in milk, granite.

3. Physical vs. Chemical Changes

  • Physical Changes:

    • The chemical composition remains unchanged; no new substance is produced.

    • Categorized into three main types:

    1. Change of Size: Cutting, tearing, crushing.

    2. Change of Shape: Bending, molding, stretching.

    3. Change of State: Melting, freezing, evaporation, condensation, sublimation, deposition.

  • Chemical Changes:

    • Involves a chemical reaction resulting in the formation of one or more new substances.

    • Five key clues indicating a chemical change:

    1. Change of Colour: An unexpected new colour appears.

    2. Change of Odour: A new or distinct smell is produced.

    3. Bubbles of Gas Produced: Gas is evolved without external boiling.

    4. A Precipitate is Produced: A solid forms when two liquids are mixed.

    5. Heat and/or Light is Released or Absorbed: An energy change occurs (exothermic or endothermic).

4. Classifying Properties

  • Qualitative Physical Property: Observed using the senses without numerical measurement.

    • Examples: Red colour, pungent odour, smooth texture, liquid state.

  • Quantitative Physical Property: Measured with instruments and expressed numerically with standard units.

    • Examples: Boiling point of water (100 ∘C100\,^\circ\text{C}), mass (50 g50\,\text{g}), density (2.70 g/cm32.70\,\text{g/cm}^3).

  • Chemical Property: Describes how a substance interacts or reacts with other chemicals.

    • Examples: Flammability, toxicity, reactivity with oxygen (rusting), reactivity with acid.

5. Solving Density Problems Using the GRASS Method

  • Density Equations:

    • Density=MassVolume\text{Density} = \frac{\text{Mass}}{\text{Volume}} or d=mVd = \frac{m}{V}

    • Mass=Density×Volume\text{Mass} = \text{Density} \times \text{Volume} or m=d×Vm = d \times V

    • Volume=MassDensity\text{Volume} = \frac{\text{Mass}}{\text{Density}} or V=mdV = \frac{m}{d}

  • GRASS Method Steps:

    • G (Given): List all known values provided in the problem along with their units.

    • R (Required): Identify the unknown variable you need to calculate.

    • A (Analysis): Write down the correct equation rearranged for the required variable.

    • S (Solve): Substitute the given values into the equation and perform the calculation.

    • S (Statement): Write a clear concluding sentence stating the final answer with proper units.