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

Pure Substances and Mixtures

Substances are formed by the same particles (either atoms or molecules). They cannot be decomposed into other substances by simple procedures. These include elements and compounds.

Mixtures are formed by two or more substances. Mixtures, whether homogeneous or heterogeneous, can always be separated by physical means such as filtration, decantation, distillation, or chromatography.

Separation Methods

Separation methods are generally categorized based on the type of mixture:

• Mechanical Methods: Most useful for heterogeneous mixtures.
• Thermal Methods: Appropriate for homogeneous mixtures.

Mechanical Separation Methods

Sedimentation

Widely used in mining to separate ore from gangue by gravity.

Settling (Decantation)

Used when

... Continue reading "Chemical Substances, Mixtures, and Physical Separation Techniques" »

Biophysics II

Colloids

Colloids are suspensions of very small particles (micelles), even much larger than the dispersed molecules within a liquid. They are also called pseudo-solutions or colloidal solutions.

State of Sol and Gel

Protoplasmic colloids undergo sol-gel processing, also called reversal or phase change. Colloids present an intermediate state between solid, liquid, and gas. States in the protoplasm of sol and gel usually alternate due to changes in concentration. The most important sols in biology are protein dispersions in water.

Types of Colloids According to the Physical State of the Phases

The dispersant phase can be a solid, liquid, or gas, just as the dispersed phase may be liquid, solid, or gaseous. The passage from a sol to a... Continue reading "Biophysics II: Colloids, Properties, and States" »

Properties of Acids

• Solutions often have a sour taste.
• They attack marble (CaCO₃) and other calcareous rocks.
• Metals react with acids, evolving hydrogen gas.
• Concentrated solutions destroy organic matter.
• They conduct electric current.
• Neutralize bases.
• Produce salts with bases.
• Change the color of acid-base indicators to red.

Properties of Bases

• Solutions often have a bitter taste.
• React with fats to form soaps, producing a soapy feel on skin.
• Generate insoluble solids with certain metals.
• Concentrated solutions destroy organic matter.
• They conduct electric current.
• Neutralize acids.
• Produce salts with acids.
• Change the color of acid-base indicators to blue.

Acid-Base Theories

Arrhenius Theory of Ionic Dissociation

In 1884, Svante Arrhenius (1859-1927) postulated,... Continue reading "Acids and Bases: Fundamental Properties, Theories, and pH Measurement" »

1. Decomposition Reactions

The scheme of a decomposition reaction is: A → B + C + ...

Decomposition reactions are those in which a substance is transformed into simpler ones due to an energy intake that can be performed in two ways:

• Thermal decomposition: Heat energy is supplied.

2Ag₂O → 4Ag + O₂

Electrolytic Decomposition: The energy provided is electric current.

CaCl₂ → Ca + Cl₂

2. Synthesis Reactions

The scheme of a synthesis reaction is: A + B + ... → C

These are reactions where two or more simple substances, elements, or compounds react to give a single compound.

3. Substitution Reactions

The scheme of a substitution reaction is: A + BC → AC + B

These are reactions in which an element of a reagent is replaced or exchanged for an element... Continue reading "Chemical Reactions: Types and Characteristics" »

Density of States

Density of states: Each value of K determines an orbital state of e-, double degeneracy due to spin. It is agreed that:

1. The electronic states always include spin degeneracy.
2. When an electron current is assumed, the electron charge of each spin is always included.
3. Electron density N is defined as the total number of electrons per unit volume.

Now the following is discussed:

1. E is a quantized continuous distribution of values, as the quantized E is increased by small integer steps of K, leading to small ΔE of the order of h².
2. Given the continuous distribution of E, the probability of a particular value of E must be zero.
3. We define the density of states n(E), which is the density of energy electrons in the range around energy E per unit

... Continue reading "Understanding Density of States, Bloch Function, and Fermi Energy" »

Chemical Bonding and Intermolecular Forces

Polarity

When two atoms with different electronegativities bond, the electrons in the bond are drawn closer to the more electronegative atom. This creates a negative charge density around that atom, which in turn causes the other atom to exhibit a positive charge density. This forms a dipole, and the bond is called polar or heteropolar.

Metallic Bonding

Various theories explain metallic bonding. The most consistent and widely accepted theory suggests that metallic bonding results from the strong attraction between a delocalized "sea" of electrons and the positively charged nuclei of the metal atoms. This explains the characteristic properties of metals, such as hardness, toughness, and malleability.

Hydrogen

... Continue reading "Understanding Chemical Bonds, Reactions, and Forces" »

Atomic Structure and Properties

Atomic Models

The concept of matter, initially considered indivisible according to Dalton, is presented with a discontinuous structure based on cathode rays (Thomson) and canal rays (Goldstein).

Rutherford considered the atom to consist of a small, hard core containing protons and neutrons, with electrons rotating around this core.

Bohr proposed that electrons in the atom are located in specific energy levels and sublevels, representing the distribution of electrons around the nucleus.

Key Atomic Definitions

Atomic Number (Z)

Atomic number (Z): Z = Number of Protons = Number of Electrons (in a neutral atom).

Mass Number (A)

Mass number (A): A = Number of Protons + Number of Neutrons.

Isotopes

Isotopes: Atoms of the same... Continue reading "Fundamental Chemistry Principles" »

Glass Manufacturing

Key Concepts in Glass Production

Glasses containing cuprous oxide have a red color.

The process used in the manufacture of glass is called continuous casting.

The most common fining agents used in glass manufacturing include nitrate and sodium antimony.

Opalescent substances commonly used in glass manufacturing include sodium silicate, cryolite, and calcium fluoride.

In glassmaking, soda ash and sodium sulfate act as fluxes.

Modern glass consists of a mixture of calcium oxide, sodium carbonate, and silica.

Bleaching agents used in glass manufacturing include manganese dioxide and selenium.

Types of Substances Used in Glassmaking

Vitrifiers: These substances transition from a crystalline structure to an amorphous structure under the... Continue reading "Glass and Paper Manufacturing Processes & Chemical Industry Overview" »

Radioactivity

Radioactive substances are characterized by emitting radiation capable of penetrating bodies that are opaque, ionizing the air, impressing photographic plates, and exciting the fluorescence of certain substances.

Alpha, Beta, and Gamma Radiation

Radioactive nuclei emit α radiation (helium nuclei), β (fast electrons), or γ (electromagnetic waves more energetic than X-rays). These radiations are ordered by their penetrating power in this way: α, β, and γ (from least to most penetrating).

Radioactive Decay

Radioactive decay is a random process. The number of nuclei, N, which have not yet disintegrated at an instant of time t is given by:

N = N₀e^-λt

The half-life, T, is the time required to disintegrate half of the initial nuclei.... Continue reading "Radioactivity, Atomic Nucleus, and Nuclear Reactions" »

Copper Production: Minerals and Processes

The minerals used in copper fabrication are primarily contained in the form of copper sulfides. Extraction is achieved via two main procedures: dry (pyrometallurgy) and wet (hydrometallurgy).

Phases of Copper Extraction

The text cites several phases involved in obtaining copper: Grinding, precipitation, dissolution, and refinement.

The choice between the wet or dry method is determined by the mineral wealth (ore grade). The dry route is used for minerals rich in copper, while the wet route is used for minerals poor in copper.

10 Key Applications of Copper

Copper is utilized in numerous industrial and mechanical applications, including:

1. Water meters
2. Turbines
3. Propellers
4. Gas meters
5. Shafts for pumps
6. Contactors
7. Relays
8. Springs
9. Gears
10. Bearings

Understanding

... Continue reading "Non-Ferrous Metals: Composition, Properties, and Uses" »