Notes, abstracts, papers, exams and problems of Chemistry

Its function is to complete the measurement circuit, providing a passage from the conductivity-sensing electrode, through the solution, to the reading device. The four parts form an electrical circuit.

Types of Electrodes

1. Hydrogen Electrode
2. Calomel Electrode: Consists of a mixture of mercury and mercurous chloride in contact with a potassium chloride solution.
3. Silver Chloride Electrode
4. Glass Electrode:
   • Parts: Lead-plated, resin-filled rod, internal electrode, sensitive glass.
5. Glass Electrode and Calomel: External calomel reference, two different cells connected in series.

Analysis Methodology

To analyze a substance using potentiometric techniques (anions, cations, organic and inorganic), the substance, or some of its possible complexes, must be electroactive... Continue reading "Potentiometric Analysis: Electrodes, Methods, and Factors" »

Understanding Chemical Bonds

Ionic Bond: This bond occurs when metallic elements interact with non-metal atoms. In this case, the metal atoms donate electrons to the non-metal atoms, becoming positively and negatively charged ions, respectively. These oppositely charged ions are attracted by strong electrical forces, being tightly bound and giving rise to an ionic compound. These electrical forces are called ionic bonds.

Covalent Bond: Covalent bonds are the forces that hold non-metallic atoms together. These atoms have many electrons in their outermost level (valence electrons) and tend to gain electrons rather than transfer them to acquire the stability of the electronic structure of a noble gas. Therefore, electrons from non-metallic atoms... Continue reading "Understanding Chemical Bonds: Ionic, Covalent, and Metallic" »

Vacuum electronics utilize various types of transducers for pressure measurement. These include bellows mechanical transducers, diaphragm transducers, thermal transducers, and ionization transducers.

Bellows and Diaphragm Transducers

Bellows and diaphragm transducers operate based on the pressure differential between atmospheric pressure and the process being measured. They can be offset relative to atmospheric pressure and calibrated in absolute units. These transducers are suitable for measuring high vacuum. They may be attached to strain gauges or capacitive elements for electrical output.

Thermal Transducers

Thermal transducers are based on the principle of proportionality between the energy dissipated from the hot surface of a filament heated... Continue reading "Vacuum Electronics: Bellows, Thermal, and Ionization Transducers" »

1. Origin of Fire

1.1. The Fire Tetrahedron

For a fire to occur, a chemical reaction between a fuel and an oxidizer is necessary, along with an activation energy. These three factors make up the fire triangle. The fire tetrahedron is formed by adding the chain reaction, which is a reaction that does not need external energy to be maintained.

• Fuel: A substance that reacts easily with an oxidizer to produce heat.
• Oxidizer: A substance that activates the fuel (e.g., oxygen).
• Activation Energy: The minimum energy required to initiate the combustion process.
• Chain Reaction: A self-sustaining reaction that does not require external energy.

Types of Fire

• Class A: Solid fuels like wood.
• Class B: Liquid or gas fuels like oil or acetylene.
• Class C: Electrical

What is Matter?

Matter is anything that occupies space and has mass. This includes land, water, air, and more. Essentially, if something exists physically, it is considered matter.

Theories of Matter

Historically, there were two main theories regarding the divisibility of matter:

• Matter is discontinuous: This theory proposed that there is a fundamental, indivisible unit of matter. This smallest unit was called an "atom."
• Matter is continuous: This theory suggested that matter could be infinitely divided into smaller and smaller parts.

It was eventually proven that matter is discontinuous, meaning atoms exist.

Thompson's Atomic Model

J.J. Thompson's model, often called the "plum pudding" model, depicted the atom as a sphere of positive charge with negatively... Continue reading "Understanding Matter: Atoms, Structure, and Properties" »

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" »