Matter, Measurement & Problem Solving

Classification of Matter

Chemistry is the study of matter and the changes it undergoes. Matter is anything that occupies space and has mass. It can be classified into three main types:

• Element: The simplest type of matter, composed of one kind of atom.

• Compound: Matter composed of two or more different elements that are chemically bonded together.

• Mixture: Matter composed of elements and/or compounds that are physically mixed together, not chemically bonded.

Mixtures can be further classified as homogeneous (uniform composition throughout) or heterogeneous (variable composition).

Example: Gatorade is a homogeneous mixture, crystalline sugar is a pure substance (compound), lead wire is a pure substance (element), and salsa is a heterogeneous mixture.

Physical and Chemical Changes

Changes in matter are categorized as physical or chemical:

• Physical Change: Alters the state or appearance without changing composition (e.g., melting, boiling, dissolving).

• Chemical Change: Alters the composition, resulting in new substances (e.g., burning, rusting, reacting with acids).

Physical changes are often reversible (e.g., melting and freezing), while chemical changes are usually irreversible (e.g., burning wood).

SI Units and Measurement

The International System of Units (SI) is the standard for scientific measurements. The seven base units are:

Perimeter, Area, and Volume

• Perimeter: Distance around an object. Formula:

• Area: Surface covered by an object. Formula:

• Volume: Space occupied by a 3D object. Formula:

Metric Prefixes

Metric prefixes are used to express multiples or fractions of base units. They are based on powers of ten:

To convert between units, use the appropriate power of ten as a conversion factor.

Significant Figures

Significant figures reflect the precision of a measurement. The rules for counting significant figures are:

• All nonzero digits are significant.

• Zeros between nonzero digits are significant.

• Leading zeros are not significant.

• Trailing zeros in a decimal number are significant.

• Exact numbers have an infinite number of significant figures.

When performing calculations:

• Multiplication/Division: The result has as many significant figures as the value with the fewest significant figures.

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

Temperature and Heat

Temperature is a measure of the average kinetic energy of particles. Heat is the transfer of thermal energy from a hotter object to a cooler one.

• Common temperature scales: Celsius (ºC), Fahrenheit (ºF), Kelvin (K).

• Conversions:

Scientific Notation

Scientific notation expresses very large or small numbers in the form , where is the coefficient (1 ≤ N < 10) and is an integer exponent.

• Positive exponent: Move decimal to the right.

• Negative exponent: Move decimal to the left.

Example:

Chemical and Physical Properties

• Chemical Property: Observed during a chemical reaction; describes the ability of a substance to change into a new substance (e.g., flammability, reactivity).

• Physical Property: Can be observed without changing the substance's chemical identity (e.g., color, density, melting point).

Intensive vs. Extensive Properties

• Intensive Properties: Independent of the amount of substance (e.g., density, temperature, color).

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

Conversion Factors and Dimensional Analysis

Conversion factors are ratios that relate two different units. Dimensional analysis is a systematic approach to problem solving that uses conversion factors to move from one unit to another.

Example: To convert 3 hours to minutes, use the conversion factor .

General steps:

1. Identify the given amount and units.

2. List the conversion factors needed.

3. Set up the calculation so units cancel appropriately.

Density

Density is the amount of mass per unit volume. It is a physical property and can be used to identify substances.

• Common units: g/cm3 for solids and liquids, g/L for gases.

Density of Geometric and Non-Geometric Objects

• For geometric objects, use formulas for volume (e.g., cube: , sphere: ).

• For irregular objects, use water displacement to find volume.

Example: If a solid displaces 60 mL of water and has a mass of 120 g, its density is .

Additional info: This guide covers foundational concepts from Chapter 1 of a general chemistry textbook, including matter classification, measurement, significant figures, SI units, properties of matter, and basic problem-solving strategies.