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

Volumetric Analysis

Requirements for Volumetric Reactions

For a reaction to be used in volumetric analysis, it must meet the following criteria:

• The reaction between the titrant and the titrated substance must be quantitative, without adding excess reagent. The reaction must be complete at the equivalence point.
• The reaction must be fast. If it is slow, it is possible to accelerate it with temperature or catalysts.
• The reaction must be stoichiometric and definite.
• To determine the endpoint, a sensitive method must be available.

Characteristics of a Standard Solution

To prepare a standard solution, there are two methods:

1. Directly dissolve a standard substance and dilute to an exact volume (using a volumetric flask).
2. Prepare a solution of approximate concentration

Introduction to Materials Science

Materials Science is an extensive discipline that relates the structure, properties, and application of engineering materials.

What are Engineering Materials?

Engineering materials are defined as those materials that, due to their desirable properties, can be used in machinery parts, structural elements, or for other engineering purposes. These materials can be structurally crystalline or amorphous and include:

• Metals
• Polymers
• Ceramics
• Composites (composed of two or more different materials from the families above)

Types of Engineering Materials

Metallic Materials

Metallic materials are substances whose atoms are joined by metallic bonds. These unique chemical bonds permit some atomic mobility and complete mobility for... Continue reading "Fundamentals of Materials Science and Engineering" »

Quantum Numbers

By solving the equations of quantum mechanics for an atom, quantum numbers appear as a mathematical consequence. These describe the behavior of electrons in the atom.

• The principal quantum number, n: Represents an energy level. It can assume any positive integer (1, 2, ...). The first level is the lowest energy, and subsequent levels, increasingly distant from the nucleus, have greater energies.
• The orbital angular momentum quantum number, l: Determines the orbital shape and energy within each level. It takes values between 0 and n-1 inclusive.
• The magnetic quantum number, m_l: Describes the orientation of the orbital in space. Among other things, it explains the splitting of spectral lines when an external magnetic field is applied.

What is a Mixture?

A mixture is a substance formed by combining two or more substances without a chemical reaction occurring that changes its components.

• A homogeneous mixture is one in which no substance loses its original properties and can be separated by physical means. It has a uniform composition throughout.
• A heterogeneous mixture is one that has a non-uniform composition in which components can be distinguished by the naked eye and consists of two or more physically distinct substances, unevenly distributed.

Physical Separation Techniques

Distillation

Distillation is used to separate two liquids with different boiling points by heating and subsequent condensation of the substances. The distillation process consists of two phases: first, the... Continue reading "Understanding Mixtures and Separation Techniques" »

The Green Revolution

The Green Revolution refers to the significant increase in agricultural productivity achieved through the use of DDT and other pesticides, fertilizers, irrigation, and mechanization.

Overfishing

Overfishing occurs when tons of fish are caught, and fish populations are unable to reproduce quickly enough to compensate.

Sustainable Forestry in Finland

Finland has developed a science and practice of forest conservation and exploitation.

Excessive CO2 Consumption

Excessive consumption of CO2 has led to imbalances, and the effects of these imbalances are well-known. The extremely rapid increase in atmospheric CO2 concentration is often called the "hockey stick" due to its shape. This increase is primarily caused by the use of fossil... Continue reading "Environmental Impacts and Sustainable Energy Sources" »

Principal Components of Iron-Carbon Alloys

The main components of iron-carbon alloys include:

• Perlite: Thin films formed with ferrite (light gray) and cementite (dark gray). Carbon content is 0.89%. Ferrite is softer, while cementite is harder.
• Ferrite: Almost pure iron, very soft, ductile, and magnetic. Its structure is cubic.
• Cementite: Located on the right side of the eutectoid point due to its carbon composition (Fe3C). It is the hardest and most fragile constituent of steel.
• Austenite
• Martensite
• Ledeburite: Consisting of cementite and austenite.

Thermal Treatments for Steel

Thermal treatments modify the properties of steel:

• Tempering: Increases hardness, toughness, and yield strength, but also increases fragility. Methods include immersion in water,

Organic Reactions

Halogenation Substitution of Alkanes

CH₄ + Cl₂ → CH₃Cl + HCl

Obtaining Alcohol from Halogenated Alkanes

CH₃-CH₂-CH₂-CH₂Cl + KOH → CH₃-CH₂-CH₂OH + KCl

Addition Reactions to Double and Triple Bonds

Hydrogenation

Hydrogen is added to alkenes and alkynes to give alkanes in the presence of a metal catalyst.

CH₃-CH=CH-CH₃ + H₂ → CH₃-CH₂-CH₂-CH₃

Halogenation

Alkenes and alkynes react with halogens to give halogenated compounds.

CH₃-CH=CH₂ + Br₂ → CH₃-CHBr-CH₂Br

Adding Hydracids

Acid hydrogen is added to the carbon with more hydrogens (Markovnikov's rule).

CH₂=CH₂ + HI → CH₃CH₂I

Water Addition

Water is added to alkenes in the presence of acid and also follows Markovnikov's rule.

Voltaic Battery

A voltaic battery is a device that allows an... Continue reading "Understanding Organic Reactions, Voltaic Cells, and Salt Hydrolysis" »

Water Hardness

Hard water is water that contains appreciable amounts of dissolved calcium and magnesium compounds. These compounds form insoluble precipitates with soap. Ion exchangers are used to remove the hardness.

Temporary Hardness

Temporary hardness is caused by the presence of calcium and magnesium bicarbonates. It can be eliminated by heating the water to precipitate the calcium carbonate:

Ca(HCO₃)₂ → CaCO₃↓ + CO₂ + H₂O

Permanent Hardness

Permanent hardness refers to the remaining calcium and magnesium salts (not bicarbonates). It requires the addition of chemicals for removal, for example:

Na₂CO₃ + CaCl₂ → CaCO₃↓ + 2NaCl

Water Pollution

Thermal Pollution

Heat, in general, is not considered a contaminant, but its effects on water can... Continue reading "Water Hardness, Pollution, Cleaners, and Sampling" »

Selectivity in Chemical Analysis

A reaction used in chemical analysis is selective when the reaction is characteristic of few substances, showing a preference for some of these. When the reaction is carried out only on a particular substance, it is specific.

Limit of Detection (LOD)

Refers to the minimum amount of a substance that can be detected in a trial.

Sensitivity of Analytical Methods

The ability of a method to discriminate a change in concentration caused by a variation in the measurement of the analytical signal.

Qualitative vs. Quantitative Analysis

The science that studies the principles and techniques of chemical analysis. It is divided into:

• Qualitative analysis: Its purpose is the identification of the constituents of a sample (organic

Key Discoveries in Atomic Theory

Thomson's Discovery of Electrons

J.J. Thomson demonstrated that atoms contain tiny, negatively charged particles called electrons. He showed that atoms could lose electrons, suggesting a static atomic model.

Rutherford's Atomic Model

Ernest Rutherford established that atoms are mostly empty space. He proposed that a small, dense region, which he named the nucleus, resides at the atom's center. This nucleus contains protons and, as Rutherford suspected, neutrons. In his model, the number of protons equals the number of electrons, with the latter orbiting the nucleus in circular paths.

The Atom as a Planetary System

The Rutherford model is analogous to a planetary system because the nucleus represents the sun, and the... Continue reading "Atomic Structure and the Periodic Table" »