General Chemistry Study Notes: Scientific Inquiry, Materials, and Chemical Reactions

Scientific Inquiry Skills

Planning Investigations

Scientific inquiry begins with careful planning to ensure that experiments are valid and reliable. Planning involves identifying the question to be answered, formulating a hypothesis, and determining the variables and controls.

• Hypothesis: A testable statement predicting the outcome of an investigation.

• Variables: Factors that can change in an experiment. Independent variable is changed by the experimenter; dependent variable is measured; controlled variables are kept constant.

• Control Group: A group in which the independent variable is not changed, used for comparison.

Example: Investigating the effect of temperature on the rate of a chemical reaction by varying temperature and measuring reaction time.

Risks, Working Safely and Ethics

Safety and ethical considerations are essential in scientific investigations. Risks must be identified and minimized, and ethical guidelines must be followed.

• Risk Assessment: Identifying potential hazards and implementing safety measures.

• Ethics: Ensuring experiments do not harm people, animals, or the environment.

Example: Wearing safety goggles and gloves when handling corrosive chemicals.

Conducting Investigations

Executing the planned experiment involves following procedures, collecting data, and making observations.

• Procedure: Step-by-step instructions for carrying out the experiment.

• Data Collection: Recording measurements and observations systematically.

Example: Measuring the mass of reactants and products in a chemical reaction.

Presenting and Evaluating Data

Data must be presented clearly and evaluated to draw valid conclusions. This includes using tables, graphs, and statistical analysis.

• Tables and Graphs: Visual representations of data to identify trends and patterns.

• Evaluation: Assessing the reliability and validity of results.

Example: Plotting reaction rate versus temperature to analyze the effect of temperature.

Materials

Atoms

Atoms are the basic building blocks of matter, consisting of protons, neutrons, and electrons.

• Atomic Structure: Protons and neutrons in the nucleus; electrons in shells around the nucleus.

• Atomic Number (Z): Number of protons in the nucleus.

• Mass Number (A): Total number of protons and neutrons.

Example: Carbon has atomic number 6 and mass number 12.

Metals, Non-metals and Metalloids

Elements are classified based on their properties as metals, non-metals, or metalloids.

• Metals: Good conductors of heat and electricity, malleable, ductile, shiny.

• Non-metals: Poor conductors, brittle, dull.

• Metalloids: Properties intermediate between metals and non-metals.

Example: Silicon is a metalloid used in electronics.

Acids and Bases

Acids and bases are important classes of compounds with distinct properties and reactions.

• Acids: Substances that release hydrogen ions ($H^+$) in solution.

• Bases: Substances that release hydroxide ions ($OH^-$) or accept $H^+$ ions.

• pH Scale: Measures acidity or basicity; $pH = - ext{log}_{10}[H^+]$.

Example: Hydrochloric acid ($HCl$) is a strong acid; sodium hydroxide ($NaOH$) is a strong base.

Chemical Reactions

Physical and Chemical Changes

Changes in matter can be classified as physical or chemical.

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

• Chemical Change: Formation of new substances with different properties (e.g., rusting iron).

Example: Burning magnesium ribbon produces magnesium oxide, a chemical change.

Types of Chemical Reactions

Chemical reactions can be classified into several types based on the changes that occur.

• Combination (Synthesis) Reaction: Two or more substances combine to form one product. $A + B \rightarrow AB$

• Decomposition Reaction: A single compound breaks down into two or more products. $AB \rightarrow A + B$

• Single Displacement Reaction: An element replaces another in a compound. $A + BC \rightarrow AC + B$

• Double Displacement Reaction: Exchange of ions between two compounds. $AB + CD \rightarrow AD + CB$

• Combustion Reaction: Substance reacts with oxygen to produce energy, often as heat and light. $CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$

Example: The reaction of hydrochloric acid with sodium hydroxide is a double displacement reaction producing sodium chloride and water.

Rates of Reaction

The rate of a chemical reaction is affected by several factors, including temperature, concentration, surface area, and catalysts.

• Rate Equation: $\text{Rate} = k[A]^m[B]^n$

• Catalyst: Substance that increases reaction rate without being consumed.

Example: Increasing temperature generally increases reaction rate due to higher kinetic energy of particles.

Acids and Bases Reactions

Acids and bases react in neutralization reactions to form salt and water.

• Neutralization Reaction: $\text{Acid} + \text{Base} \rightarrow \text{Salt} + \text{Water}$

Example: $HCl + NaOH \rightarrow NaCl + H_2O$

Table: Classification of Elements

Type	Properties	Examples
Metals	Conductive, malleable, ductile, shiny	Iron, Copper, Gold
Non-metals	Poor conductors, brittle, dull	Oxygen, Sulfur, Carbon
Metalloids	Intermediate properties	Silicon, Boron

Table: Types of Chemical Reactions

Reaction Type	General Equation	Example
Combination	$A + B \rightarrow AB$	$2H_2 + O_2 \rightarrow 2H_2O$
Decomposition	$AB \rightarrow A + B$	$2H_2O \rightarrow 2H_2 + O_2$
Single Displacement	$A + BC \rightarrow AC + B$	$Zn + 2HCl \rightarrow ZnCl_2 + H_2$
Double Displacement	$AB + CD \rightarrow AD + CB$	$AgNO_3 + NaCl \rightarrow AgCl + NaNO_3$
Combustion	$CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$	Methane burning in air

Additional info: These notes are based on the table of contents and introductory material from a science textbook, with academic context added to ensure completeness and relevance for General Chemistry students.