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

Chemicals

Evaporation

Evaporation is a physical process involving a state change from liquid to gas, in which substances can be separated based on their boiling points.

For the transition of a liquid to a gaseous state from liquid surfaces or from the ground, see: Evaporation (hydrology).

Redox

Oxidation-reduction reactions (also known as redox reactions) are electron transfer reactions. This transfer occurs between a set of chemical elements: an oxidant and a reductant (a reduced form and an oxidized form, respectively).

For a redox reaction to occur, the system must contain an element that yields electrons and another that accepts them:

• The oxidizing agent is a chemical element that tends to capture these electrons, resulting in a lower oxidation

Fundamentals of Solid-Liquid Extraction

Key Applications in Various Industries

• Extraction of sugar from sugar beets
• Coffee decaffeination
• Extraction of essential oils from herbs and botanicals
• Recovery of oils from seeds and other materials
• Obtaining pectin (for jelly) from fruit fractions

Commonly Used Solvents

• Water
• Hexane
• Heptane
• Ether
• Chloroform
• Benzene
• Ethanol

Industrial Extractor Equipment Designs

Static Bed Extractors

These extractors operate with a stationary solid bed through which the solvent passes.

Simple Contact Extractors

These operate discontinuously and are simple in design. They consist of a double-bottom tank where the solid material is placed. A liquid solvent is sprayed over the solid and percolates through it by gravity. The solvent, now... Continue reading "Industrial Extractor Technologies: Methods & Applications" »

Previous Concepts

Stress: The applied force per unit area.

Elongation: Deformation of a material under the action of a force.

Reduction in Area: The decrease in cross-sectional area.

General Properties

• Impenetrability: The volume occupied by a body cannot be occupied by another simultaneously.
• Severability: Divisible parts can be increasingly smaller.
• Porosity: Having pores.
• Compressibility: The ability of bodies to decrease their volume by applying pressure.
• Affinity: The force that unites similar materials.
• Adhesion: Attraction established between bodies whose surfaces are in contact.
• Solubility: The ability to dissolve and disperse within a liquid.
• Specific Gravity: The ratio of a body's weight to the weight of an equal volume of a reference substance.

Atoms, Bonding, and Molecular Crystals

Ancient history knew elements such as gold, silver, etc. Over time, more elements were discovered; currently, over a hundred are known. A basic classification of elements, based on their appearance and physical properties, allows us to divide them into two main groups: metals and non-metals.

Metals and Non-Metals

To distinguish these groups, we examine their differing characteristic features.

1. Metallic Elements

• They have a characteristic luster.
• They are opaque and good conductors of heat and electricity.
• They are solid at ambient temperature and usually tend to have high melting points.

2. Non-Metallic Elements

• They do not have metallic luster.
• They are poor conductors of heat and electricity.
• At ambient temperature,

Fundamental Atomic Concepts

Atomic Number and Mass Number

Two fundamental properties of an atom are its atomic number and mass number.

• The Atomic Number (Z): This is the number of protons in the nucleus of an atom. For example, a neutral Sodium atom (Na) with atomic number 11 has 11 protons and 11 electrons.
• The Mass Number (A): This is the total number of protons and neutrons in the nucleus of an atom. For example, Sodium-23 (²³Na) has a mass number of 23.

The number of neutrons can be calculated by subtracting the atomic number from the mass number (A - Z).

The Atom, Molecule, and Orbitals

The Atom

In physics and chemistry, an atom is the smallest unit of a chemical element that retains its identity and properties. It cannot be divided further by... Continue reading "Atomic Structure and Electron Configuration Principles" »

Atomic Model Evolution

Democritus's Atomic Theory

Democritus proposed that matter could not be divided into smaller pieces forever. He believed that there were tiny, eternal, invisible, and indivisible particles called atoms (meaning indivisible in Greek) that constituted all matter.

Dalton's Atomic Theory (1808)

• Matter is made of indivisible and indestructible particles called atoms.
• All atoms of an element are identical.
• Atoms of different elements combine in fixed proportions to form compounds.

Thomson's Atomic Model (1897)

J.J. Thomson experimentally verified the existence of the electron. He discovered that the electron's mass was much lower than that of atoms, suggesting that atoms possessed a negative charge and were divisible. His model described... Continue reading "Atomic Model Evolution and Chemical Bonding" »

Understanding Human Growth Curves and Body Types

4.1. The Emerging Growth Curve

Each variable of interest (weight, height, etc.) can be related to different ages, defining what is called the emerging growth curve. This curve is intended to gain insight into the process of the acquisition of some variables over the years.

4.2. The Velocity Curve: Measuring Physical Growth Rate

The velocity curve (or physical growth curve) shows the amount gained (rate) each year (e.g., in cm, g, or kg). In a typical curve of growth rate, specific moments are expressed:

• Slowdown
• Stability
• Acceleration
• Culmination point of growth (peak velocity)
• Final growth stage

4.3. Body Proportions and Differential Growth Rates

In the study of human growth, the body and its parts do... Continue reading "Human Growth and Development: Curves, Rates, and Somatotype Classification" »

Fundamental Chemical Principles: Acid-Base Theories

Arrhenius Theory: Ionic Dissociation

The Arrhenius theory postulates the existence of positive and negative ions in aqueous solutions of acids, bases, and salts (electrolytes) to explain their electrical conductivity.

Key Definitions in Arrhenius Theory

• Acid: A substance, electrically neutral, that in aqueous solution dissociates into $ ext{H}^+$ ions (protons) and negative ions.
• Base: A substance, electrically neutral, that in aqueous solution dissociates into $ ext{OH}^-$ ions (hydroxide or hydroxyl ions) and positive ions.

Neutralization Reaction (Arrhenius)

According to this theory, the neutralization reaction occurs between an acid and a base, yielding a salt and water.

Brønsted-Lowry Theory:

The Calvin Cycle

The Calvin cycle's objective is to fix carbon dioxide (CO2) using ribulose-1,5-bisphosphate. For every triose (3-carbon sugar), two are needed to form a glucose, requiring 3 ribulose and 3 CO2. A hexose (6-carbon sugar) requires 6 ribulose and 6 CO2.

Phases of the Calvin Cycle

1. Carbon Fixation: Ribulose-1,5-bisphosphate (5C) combines with CO2 to form a 6C compound. Enzyme: Ribulose bisphosphate carboxylase. This creates a highly unstable compound. Input: 1 CO2 per ribulose.
2. Reduction: The unstable 6C compound splits into two triose molecules (3C), specifically glyceraldehyde-3-phosphate. Input/Output: None.
3. Phosphorylation: Glyceraldehyde-3-phosphate is phosphorylated using ATP, transforming into 1,3-bisphosphoglycerate. Input: 1

Q: Explain in detail the interaction of hydrophobic or hydrophobic effect. Is it a chemical bond? Explain your answer. Discuss the importance of this phenomenon in the formation and stability of biological membranes.
Hydrophobic Effect: The tendency of nonpolar molecules to cluster in polar solvents like H₂O for energetic reasons. Nonpolar substances tend to associate with one another in aqueous solutions because this results in fewer water molecules being involved in the cage that surrounds them. This situation is thermodynamically favored as it leads to lower order due to fewer water molecules (i.e., the entropy is higher) compared to when each polar molecule is surrounded by individual water molecules.
It is a chemical bond since it is... Continue reading "Understanding Hydrophobic Effects and Stereoisomerism in Chemistry" »