Ch.1 - Introduction: Matter & Measurement

Classification of Matter

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

• Pure Substances: Matter with a fixed composition and distinct properties. Examples include elements and compounds.

• Mixtures: Physical combinations of two or more substances where each retains its own identity and properties. Mixtures can be homogeneous (uniform composition, e.g., salt water) or heterogeneous (non-uniform composition, e.g., salad).

Example: Classify the following substances:

• Gatorade – Homogeneous mixture

• Crystalline sugar – Pure substance (compound)

• Lead wire – Pure substance (element)

• Salsa – Heterogeneous mixture

Physical and Chemical Changes

Changes in matter can be classified as physical or chemical based on whether the composition of the substance changes.

Physical Changes

• Changes that do not alter the chemical composition of a substance.

• Examples: Melting ice, dissolving sugar in water, tearing paper.

Chemical Changes

• Changes that result in the formation of new substances with different properties.

• Examples: Burning wood, rusting iron, cooking an egg.

Reversible and Irreversible Changes

• Reversible Changes: Can be undone, such as phase changes (melting, freezing, boiling).

• Irreversible Changes: Cannot be undone by simple physical means, such as burning paper or cooking an egg.

Chemical Properties

Chemical properties describe a substance's ability to undergo chemical changes and form new substances.

• Examples: Reactivity with acids, flammability, oxidation states.

• Observed only during a chemical reaction.

Physical Properties

Physical properties can be observed or measured without changing the substance's identity.

• Examples: Color, melting point, density, boiling point, state of matter at room temperature.

Intensive vs. Extensive Properties

• Intensive Properties: Do not depend on the amount of substance present (e.g., density, melting point, color).

• Extensive Properties: Depend on the amount of substance present (e.g., mass, volume, energy).

SI Units and Measurements

The International System of Units (SI) is the standard for scientific measurements. It is based on seven base units.

Common derived units include area (m2), volume (m3), and density (kg/m3).

Metric Prefixes

Metric prefixes are used to express multiples or fractions of base units.

Example: Convert 654 kg to g:

Temperature and Thermal Energy

• Thermal Energy: The sum of kinetic and potential energies of all atoms in an object.

• Temperature: The average kinetic energy of the particles in a substance.

Temperature is measured in kelvin (K), Celsius (°C), or Fahrenheit (°F).

Scientific Notation

Scientific notation expresses very large or small numbers in the form , where and is an integer.

• Move the decimal point to create a coefficient between 1 and 10.

• Count the number of places moved to determine the exponent.

Example:

Significant Figures

Significant figures (sig figs) are the digits in a measurement that are known with certainty plus one estimated digit.

• All nonzero digits are significant.

• Zeros between nonzero digits are significant.

• Leading zeros are not significant.

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

Example: 0.00364 has 3 significant figures.

Significant Figures in Calculations

• Multiplication/Division: The result should have as many sig figs as the value with the fewest sig figs.

• Addition/Subtraction: The result should have as many decimal places as the value with the fewest decimal places.

Conversion Factors and Dimensional Analysis

Conversion factors are ratios used to express a quantity in different units. Dimensional analysis is a systematic approach to problem-solving that uses conversion factors to move from one unit to another.

• Set up the problem so that units cancel appropriately.

• Multiply by conversion factors until the desired unit is obtained.

Example: To convert 115 minutes to hours:

Density

Density is the amount of mass per unit volume of a substance.

Formula:

• For solids and liquids, units are typically g/cm3 or g/mL.

• For gases, units are typically g/L.

Example: If a metal has a density of 2.14 g/cm3, its density in kg/m3 is:

Density of Geometric and Non-Geometric Objects

• For regular shapes, use geometric formulas for volume (e.g., for a rectangular prism).

• For irregular shapes, use water displacement to determine volume.

Example: If a cube of silver (density = 10.5 g/cm3) measures 0.36 cm on each side, its mass is:

Summary Table: Key Concepts

Additional info: These notes are based on "Brown - Chemistry: The Central Science" and cover foundational concepts for General Chemistry, including classification of matter, physical and chemical properties and changes, SI units, measurements, scientific notation, significant figures, conversion factors, dimensional analysis, and density calculations.