Notes, summaries, assignments, exams, and problems for Chemistry

Scientific Method

Ask a question.

Research.

Make a hypothesis.

Experiment and test your hypothesis.

Analyze your test results.

Present a conclusion.

Chemistry

Chemistry is the branch of science that studies the properties of matter and how matter interacts with energy.

Organic Chemistry

The branch of chemistry concerned with the study of compounds that contain the element carbon.

Inorganic Chemistry

The branch of chemistry concerned with the study of materials that contain any combination of chemical elements.

Element

A substance that cannot be broken into two or more simpler substances by any physical or chemical method and made of the same kind of atoms.

Compound

A molecule of a pure substance that contains two or more elements combined.

Heterogeneous Mixture

A... Continue reading "Scientific Method and Chemistry: An Introduction to Matter and Atoms" »

Halogenation

Halogenation: The reaction of an alkane with a halogen (X2 = F, Cl, Br, I) occurs when a mixture of the two is irradiated with ultraviolet light.

Combustion

Combustion: The reaction of an alkane with O2 occurs during combustion when the alkane is used as a fuel. Carbon dioxide and water are formed as products, and a large amount of heat is released.

An example of a combustion reaction:

CH4 + 2 O2 → CO2 + 2 H2O + Energy

Complete

Complete: C2H6 (g) + O2 (g) → CO2 (g) + H2O (g) + Energy

Incomplete

Incomplete: C3H8 (g) + O2 (g) → H2O (g) + CO2 (g) + CO (g) + C (s) + Energy

Petroleum

Petroleum: Complex mixture of alkanes that can be separated into fractions by distillation. Separating molecules based on differences in boiling points is called... Continue reading "Halogenation, Combustion, Complete and Incomplete Reactions, Petroleum, Refining, Alkenes" »

Water Properties and Ocean Chemistry

Water's High Heat Capacity

21. Coastal Climate Moderation

Which property of water causes coastal communities to have only moderate differences in daily highs and lows when compared to inland communities?

Answer: A) High heat capacity.

22. Water's Heat Capacity Compared to Other Liquids

In comparison to most other liquids, the heat capacity of water is:

Answer: A) Higher than other liquids.

Seawater Composition and Buffering

23. Principle of Constant Proportions

The Principle of Constant Proportions states that:

Answer: D) The relative concentration of seawater ions does not change.

25. Seawater Buffer Ion

The ion in seawater that serves as a buffer is:

Answer: D) HCO3-.

Water Phase Changes

24. Temperature Change During

Metal Corrosion

Corrosion is the rusting of metal or alloy due to moisture and air. When it contacts air and water, a reaction forms a layer on the surface. For example, when an iron rod contacts air and moisture, it reacts and forms ferric oxide (Fe₂O₃) on its surface. It can be prevented by using alloys like stainless steel, brass, or bronze, painting the metal, applying oil, or coating with galvanized zinc.

Chemical Reactions

Some reactions happen very fast, like the precipitation of silver chloride, which occurs immediately after mixing aqueous solutions of silver nitrate and sodium chloride. Other reactions, like the rusting of iron in the presence of air and moisture, are very slow. Some reactions have a moderate rate.

The rate of a chemical... Continue reading "Metal Corrosion, Chemical Reactions, and Electrochemistry" »

Scalars and Vectors

What is a scalar? A scalar is a quantity that is fully described by a magnitude only. It is described by just a single number. Some examples of scalar quantities include speed, volume, mass, temperature, power, energy, and time.

What is a vector? A vector is a quantity that has both a magnitude and a direction. Vector quantities are important in the study of motion. Some examples of vector quantities include force, velocity, acceleration, displacement, and momentum.

Endothermic and Exothermic Reactions

An endothermic reaction takes place when energy is absorbed from the surroundings in the form of heat. An exothermic reaction is when energy is released from the system into the surroundings.

Endothermic reactions must be supplied... Continue reading "Scalars, Vectors, Endothermic & Exothermic Reactions Explained" »

Atomic Structure

Elements are a type of atom. Atoms are made up of protons, neutrons, and electrons. The nucleus is the center of an atom.

• Proton: +1 charge
• Electron: -1 charge
• Neutron: 0 charge (neutral)

Rutherford (1911) conducted the gold foil experiment.

Different elements have different numbers of protons in the nucleus.

• Atomic number (Z): Number of protons
• Mass number (A): Number of protons + Number of neutrons

Z

Chemical Symbol

A

Neutron number = Mass number - Atomic number

The number of neutrons can change (protons stay the same) in a given atom, making them isotopes.

Atomic mass is the total mass of elements and all its isotopes. U represents atomic mass units.

A radioactive isotope consists of nuclides whose nuclei undergo spontaneous decay.

Three

Foundational Concepts of Atomic Structure

Discovery of Subatomic Particles

• Electron: Discovered by J. J. Thomson (1897). Relative mass: 1/1837. Mass: 9.1 x 10⁻³¹ kg. Charge: -1.
• Proton: Discovered by Ernest Rutherford (1920). Relative mass: 1 atomic mass unit (u). Mass: 1.7 x 10⁻²⁷ kg. Charge: +1.
• Neutron: Discovered by James Chadwick (1932). Relative mass: 1 atomic mass unit (u). Mass: 1.7 x 10⁻²⁷ kg. Charge: 0.

Rutherford's Planetary Model (1911)

Ernest Rutherford proposed the Planetary Model, which is accepted today as the basic structure of the atom.

The atom consists of a very small central region, the nucleus, containing protons and neutrons, surrounded by orbiting electrons. The number of electrons equals the number of protons... Continue reading "Fundamentals of Atomic Structure and Periodic Trends" »

What is Surface Engineering?

Definition: It is the sub-discipline of material science which deals with the surface of solid matter.

Objectives: Involves altering the properties of the surface phase to reduce degradation over time, making it robust to the environment.

Applications: Automotive, aerospace, missile, power, electronic, biomedical, textile, petroleum, chemical, steel, power. Used in almost all types of materials.

Describe SEM and TEM

SEM: Scanning Electron Microscopy images the sample surface by scanning it with a high-energy beam of electrons. Advantages include 3D imaging and greater depth of focus. Disadvantages include low resolution and expensive equipment. Applications include gunshot residue analysis and firearms identification.... Continue reading "Surface Engineering and Microscopy Techniques in Material Science" »

Stoichiometry and Fixed Ratios

Fixed Ratios in Building and Manufacturing

Describe an experience you’ve had making or building something where the amount of each ingredient or building block came in fixed ratios.

Building a model airplane is an example. For each model, there must be two wings and three wheels. In order for the model to look correct or work properly, there must be a certain, unvarying number of wings and wheels.

Direct Arithmetic Units in Chemical Problems

A chemical problem may be presented to you in units of moles, mass, or volume. Which one of these can be directly used in your arithmetic no matter what the conditions are?

Moles can be directly used. The number of molecules or moles is the basic unit used in solving chemical... Continue reading "Chemical Calculations and Gas Law Principles: Stoichiometry and Kinetic Theory" »