General Chemistry I: Unit 1 Study Guide

Unit 1: Foundations of General Chemistry

Density Calculations

Density is a fundamental property of matter, defined as the mass of a substance per unit volume. It is commonly used to identify substances and assess purity.

• Definition: Density ($d$) is calculated as mass ($m$) divided by volume ($V$).

• Formula:

$d = \frac{m}{V}$

• Units: Commonly expressed in g/cm3 or kg/L.

• Example: If a sample has a mass of 10.0 g and a volume of 2.0 cm3, its density is $\frac{10.0\ \text{g}}{2.0\ \text{cm}^3} = 5.0\ \text{g/cm}^3$.

Dimensional Analysis

Dimensional analysis is a method used to convert one unit of measurement to another using conversion factors.

• Key Steps:

  1. Identify the given quantity and units.

  2. Multiply by conversion factors so that units cancel appropriately.

  3. Continue until the desired units are obtained.

• Example: Convert 25.0 inches to centimeters. (1 inch = 2.54 cm)

$25.0\ \text{inches} \times \frac{2.54\ \text{cm}}{1\ \text{inch}} = 63.5\ \text{cm}$

Analysis of Glassware

Laboratory glassware is used for measuring, mixing, and storing chemicals. Understanding the correct use and limitations of each type is essential for accurate measurements.

• Types: Beakers, graduated cylinders, volumetric flasks, pipettes, burettes.

• Accuracy: Volumetric flasks and pipettes are more accurate than beakers and graduated cylinders.

• Example: Use a volumetric flask for preparing standard solutions; use a graduated cylinder for approximate volume measurements.

Classification of Substances

Substances can be classified based on their composition and properties.

• Pure Substances: Elements and compounds with a fixed composition.

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

• Example: Water (H2O) is a compound; air is a homogeneous mixture.

Recording Measurements

Proper recording of measurements includes all certain digits and one estimated digit (significant figures).

• Significant Figures: Reflect the precision of a measurement.

• Example: If a graduated cylinder reads between 21 and 22 mL, and the meniscus is estimated at 21.6 mL, record as 21.6 mL (3 significant figures).

Intensive and Extensive Properties

Physical properties of matter are classified as intensive or extensive.

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

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

• Example: The density of gold is always 19.3 g/cm3, regardless of sample size.

Precision of Data

Precision refers to the consistency of repeated measurements, while accuracy refers to how close a measurement is to the true value.

• Precision: High precision means measurements are close to each other.

• Accuracy: High accuracy means measurements are close to the accepted value.

• Example: If three mass measurements are 2.01 g, 2.00 g, and 2.02 g, they are precise.

Physical vs. Chemical Change

Changes in matter are classified as physical or chemical.

• Physical Change: Alters the form or appearance but not the composition (e.g., melting, dissolving).

• Chemical Change: Produces new substances with different properties (e.g., rusting, combustion).

• Example: Ice melting is a physical change; iron rusting is a chemical change.

Compound Naming

Naming compounds follows specific rules depending on the type (ionic, covalent, acids).

• Ionic Compounds: Name the cation first, then the anion (e.g., NaCl: sodium chloride).

• Covalent Compounds: Use prefixes to indicate the number of atoms (e.g., CO2: carbon dioxide).

• Acids: If the anion ends in -ide, the acid name begins with hydro- and ends with -ic (e.g., HCl: hydrochloric acid).

Matching: Physical vs. Chemical, Intensive vs. Extensive

Understanding the differences between these classifications is essential for analyzing matter.

• Physical vs. Chemical Properties: Physical properties can be observed without changing the substance; chemical properties describe reactivity.

• Intensive vs. Extensive: See above for definitions.

Matching: Separation Techniques

Mixtures can be separated by physical means based on differences in properties.

• Filtration: Separates solids from liquids.

• Distillation: Separates substances based on boiling points.

• Chromatography: Separates based on movement through a medium.

• Example: Saltwater can be separated by distillation.

Matching: Phases of Matter

Matter exists in different physical states, each with distinct properties.

• Solid: Definite shape and volume.

• Liquid: Definite volume, takes shape of container.

• Gas: No definite shape or volume.

• Example: Ice (solid), water (liquid), steam (gas).

Matching: Metals vs. Nonmetals

Elements are broadly classified as metals or nonmetals based on their properties.

Property	Metals	Nonmetals
Conductivity	Good conductors	Poor conductors
Malleability	Malleable, ductile	Brittle (if solid)
Appearance	Lustrous (shiny)	Dull
Location on Periodic Table	Left and center	Right side

• Example: Iron is a metal; oxygen is a nonmetal.