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

Water Quality Definitions

Alkalinity

Alkalinity: A measure of the water’s capability to absorb hydrogen ions without significant pH change (buffering capacity).

Problem 7-4: Settling Tank Design for Stillwater Water Plant Expansion

Design the settling tank(s) for the City of Stillwater’s water treatment plant expansion using the design overflow rate found in Example 7-3. The maximum day design flow is 0.5 m³/s. Assume a water temperature of 10° C.

Design Calculation Steps (Set 1)

1. Find the Surface Area

   Calculation: (0.5 m³/s) × (86,400 s/d) = 43,200 m³/d

2. Select the Number of Tanks

   

   = 221.66 or 222 m²/tank

3. Select a Trial Width for Calculation

   The maximum width for the chain-and-flight sludge collector is 6 m increments. Assume a width of 4 m.

4. Check

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

Physical States of Matter

Physical States: Solid (Stones, salt, copper) / Liquid (Water, alcohol, gasoline) / Gaseous (Nitrogen, oxygen, hydrogen)

Do they have a fixed shape? Yes/No/No. Do they have a fixed volume? Yes/Yes/No. Are they easily compressible? No/No/Yes. Do they expand? No/No/Yes.

Kinetic Theory of Matter

Kinetic Matter is formed by very small particles (atoms) that are invisible even when using microscopes. The particles are in continuous movement. The higher the temperature, the faster they move. There are forces of attraction between the particles that make them group together. The farther the distance between the particles, the stronger these forces become.

States of Movement of the Particles:

• Speed of movement: Low, medium, high.

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" »

Stoichiometry, Yields and Reaction Types

Solution

Solution — This is obtained when one chemical becomes completely dissolved in another.

Theoretical Yield

Theoretical yield — If a chemist calculates the maximum amount of product that could be obtained in a chemical reaction, he or she is calculating the theoretical yield.

Stoichiometry

Stoichiometry — Terms used to designate the calculations of quantities of substances involved in chemical reactions.

Percent Yield

Percent yield — This is obtained by dividing the actual yield by the theoretical yield and multiplying by 100%.

Limiting Reactant

Limiting reactant — The reactant that is fully consumed during the reaction.

Practice Questions

1.1 — In the equation 6 CO₂ + 6 H₂O ... the mole ratio... Continue reading "Stoichiometry, Reaction Types, and Yield Calculations" »

Kinetic Theory of Matter

• Matter is made up of particles.
• These particles are constantly moving because they have kinetic energy.
• There are spaces between the particles.
• There are attractive forces between particles, and these become stronger as the particles move closer.
• All particles have energy. The temperature of a substance is a measure of the average kinetic energy of the particles.
• A change in phase may occur when the energy of the particles is changed.

Boyle's Law

The pressure of a fixed quantity of gas is inversely proportional to the volume it occupies, as long as the temperature remains constant. P₁ × V₁ = P₂ × V₂

Gay-Lussac's and Charles's Law

The volume of an enclosed sample of gas is directly proportional to its absolute temperature, provided... Continue reading "Matter: Kinetic Theory, Properties, and Classifications" »