Ch. 1 Study Notes: Matter and Measurements

Ch. 1: Matter and Measurements

Classification of Matter

Matter is anything that has mass and occupies space. It can be classified based on its physical state and composition.

• States of Matter: Solid, liquid, and gas.

• Pure Substances: Elements and compounds with fixed composition.

• Mixtures: Physical combinations of two or more substances; can be homogeneous (solutions) or heterogeneous.

• Example: Air is a homogeneous mixture; sand and iron filings form a heterogeneous mixture.

Physical and Chemical Properties/Changes

Properties and changes in matter are classified as physical or chemical.

• Physical Properties: Characteristics observed without changing the substance's identity (e.g., color, melting point, density).

• Chemical Properties: Describe a substance's ability to undergo chemical changes (e.g., flammability, reactivity).

• Physical Change: Change in state or appearance without altering composition (e.g., melting ice).

• Chemical Change: Transformation resulting in new substances (e.g., rusting iron).

• Example: Dissolving sugar in water is a physical change; burning wood is a chemical change.

Converting Numbers with Different Prefixes/Units

Scientific measurements use SI units and prefixes to indicate magnitude.

• Common SI Prefixes: kilo- (k, $10^3$), centi- (c, $10^{-2}$), milli- (m, $10^{-3}$), micro- ($ext{μ}$, $10^{-6}$).

• Unit Conversion: Use conversion factors to change between units.

• Example: $1~ ext{km} = 1000~ ext{m}$; $1~ ext{cm} = 0.01~ ext{m}$.

Significant Figures (SF) in Measurement

Significant figures reflect the precision of a measured value.

• Definition: All the digits in a measurement that are known, plus one estimated digit.

• Rules:

  • Nonzero digits are always significant.

  • Zeros between nonzero digits are significant.

  • Leading zeros are not significant.

  • Trailing zeros are significant only if there is a decimal point.

• Example: 0.00450 has three significant figures.

Using Significant Figures in Calculations

Calculations must reflect the correct number of significant figures.

• Addition/Subtraction: Result has the same number of decimal places as the measurement with the fewest decimal places.

• Multiplication/Division: Result has the same number of significant figures as the measurement with the fewest significant figures.

• Example: $2.5 imes 3.42 = 8.6$ (two significant figures).

Density, Temperature, and Heat Calculations

These measurements are fundamental in chemistry for characterizing substances and energy changes.

• Density ($d$): Mass per unit volume. Equation: $d = \frac{m}{V}$ Example: If $m = 10~\text{g}$ and $V = 2~\text{cm}^3$, $d = 5~\text{g/cm}^3$.

• Temperature: Measured in Celsius ($^\circ$C), Kelvin (K), or Fahrenheit ($^\circ$F). Conversion: $K = ^\circ C + 273.15$

• Heat Calculations: Use specific heat capacity ($c$) to calculate heat ($q$) absorbed or released. Equation: $q = m \times c \times \Delta T$ Example: $q = 50~\text{g} \times 4.18~\text{J/g}^\circ\text{C} \times 10^\circ\text{C} = 2090~\text{J}$

Property	Physical	Chemical
Definition	Observed without changing identity	Describes chemical reactivity
Examples	Color, melting point, density	Flammability, oxidation

Additional info: These topics form the foundation for understanding measurements and properties in chemistry, essential for all subsequent chapters.