Introduction to Chemistry

What is Chemistry?

Chemistry is the scientific study of the composition, structure, properties, and reactions of matter. It is a central science that connects physical sciences with life sciences and applied sciences such as medicine and engineering.

• Chemical: Any material used in or produced by a chemical process.

• Examples in Everyday Life: Toothpaste (contains chemicals like sodium monofluorophosphate), cleaning agents, medicines, and food additives.

Additional info: Chemistry-produced items are encountered daily, from the air we breathe to the products we use.

Key Terms and Definitions

• Matter: Anything that has mass and occupies space.

• Atoms: The smallest units of matter that retain the properties of an element.

• Molecules: Groups of atoms chemically bonded together.

Additional info: All matter is composed of atoms, which combine to form molecules.

Scientific Method in Chemistry

Steps of the Scientific Method

The scientific method is a systematic approach used to investigate phenomena, acquire new knowledge, or correct and integrate previous knowledge.

• Observations: Gathering data through the senses or instruments.

• Formulate Hypothesis: Proposing a tentative explanation based on observations.

• Experiment (Test): Conducting controlled tests to support or refute the hypothesis.

• Law (Theory): Developing principles that explain and predict phenomena.

Example: Scurvy was prevented by eating fresh fruits, leading to the discovery of Vitamin C.

Law of Conservation of Mass

In a chemical reaction, matter is neither created nor destroyed.

• Equation:

Units and Measurement

Types of Measurement Systems

Measurements in chemistry use standardized units to ensure consistency and accuracy.

• English System: Used primarily in the United States (e.g., inches, pounds).

• Metric System: Used worldwide (e.g., meters, grams).

• SI (Système International): Based on the metric system, used in scientific contexts.

Metric Prefixes

Metric prefixes indicate multiples or fractions of units.

Scientific Notation

Scientific notation expresses very large or small numbers in the form .

• Example: Diameter of the Earth = m

• Small numbers:

Additional info: The exponent indicates the number of times the decimal was moved.

Units of Measurement

Volume

Volume is the amount of space a substance occupies.

• Formula for volume of a cube:

• Conversion:

Mass vs. Weight

• Mass: The amount of matter in an object (measured in kilograms or grams).

• Weight: The force exerted by gravity on an object (measured in newtons or pounds).

Additional info: Mass is constant; weight varies with gravity.

Density

Definition and Formula

Density is a physical property that can be used to identify substances.

• Formula:

• Units: g/mL or g/cm3

Examples:

• Density of isopropyl alcohol: 0.79 g/mL

• Density of liquid water: 1.0 g/mL

• Density of ice: 0.99 g/mL

Measuring and Recording Quantities

Equipment and Estimation

Measurements should be recorded to the correct number of decimal places, estimating one digit beyond the smallest scale division.

• Example: If a graduated cylinder shows 21.2 mL, estimate to 21.21 mL.

Significant Figures

Significant figures (sig figs) indicate the precision of a measurement.

• Nonzero digits are always significant.

• Leading zeros are not significant.

• Trailing zeros after a decimal point are significant.

• Trailing zeros before a decimal point may be ambiguous.

Sig Figs in Calculations

• Addition/Subtraction: Use the fewest decimal places.

• Multiplication/Division: Use the fewest sig figs.

• Rounding: Round only the final answer.

Unit Conversion and Dimensional Analysis

Conversion Factors

Conversion factors are ratios used to express quantities in different units.

• Example: 1 dozen = 12 eggs

• To convert units, multiply across the top and divide across the bottom, canceling units as needed.

Dimensional Analysis

Dimensional analysis is a method for converting between units using conversion factors.

• Example: To convert 3 dozen eggs to individual eggs:

Applications and Practice Problems

Common Conversions and Calculations

• Converting mass from pounds to kilograms:

• Calculating volume, mass, and dosage in medical and laboratory settings.

• Using density to find mass or volume:

Example: A patient weighs 111 lb. How many kg is this? kg

Example: A doctor prescribes 4 mg/kg of Bacitracin to a 153 lb patient. Convert lb to kg, then multiply by dosage.

Two-Step Conversion Problems

• Convert between units and apply dosage calculations.

• Example: Calculate the amount of medication for a patient based on body weight and prescribed dosage.

Summary Table: Common Units and Conversions

Additional info: These conversions are essential for laboratory and clinical calculations in GOB Chemistry.