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

States of Matter and Their Properties

Solids: Maintain a constant volume and shape. They possess a high density, are rigid, and are difficult to compress. Liquids: Are not rigid and are difficult to compress, maintaining a constant volume but with a variable shape. They usually have a high density. Gases: Easily expand and compress, having a variable shape and very low density.

Kinetic Molecular Theory

The discontinuous kinetic molecular model (composed of many particles) explains the behavior of matter. Molecules are in continuous motion, with attractive forces between particles. Solids: The attraction between particles is very intense, keeping them very close together and occupying a fixed position. Their movement is limited to vibration. Liquids:

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.

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" »

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" »

Properties of Ionic, Covalent, and Metallic Substances

Ionic Substances

Thermal Stability: Ionic compounds are typically solid at room temperature and pressure due to strong electrostatic attractions between ions, resulting in high melting and boiling points. The greater the charge of the ions and the smaller the distance between them, the higher the melting and boiling points.

Solubility: Polar solvents can reduce the attractive forces between ions by interposing solvent molecules. Each ion becomes surrounded by solvent molecules (solvation). Solubility decreases with increasing charge of the ions. Therefore, substances containing Group IIA metals (alkaline earth metals) are generally less soluble than those formed by Group IA metals (alkali... Continue reading "Ionic, Covalent, and Metallic Substances: Properties Compared" »

Emission and Absorption Spectra

The elements emit energy in the form of electromagnetic radiation, but only at a few specific frequencies. Elements also absorb specific frequencies when illuminated with electromagnetic radiation.

The de Broglie Hypothesis

The de Broglie hypothesis expanded the dual behavior of radiation, suggesting that matter, especially electrons, also exhibits both particle and wave aspects. According to this hypothesis, the energy of both matter and radiation is related to the frequency (f) of the wave associated with their movement through the expression E = hf. Thus, the wavelength associated with a material particle or photon momentum is λ = h / p.

The Uncertainty Principle

The principle of indeterminacy, or uncertainty... Continue reading "Atomic Spectra, Radioactivity, and Nuclear Reactions" »

Concentration Changes During Assessment

During an assessment, there must be an abrupt change in some property of the reaction mixture at the equivalence point. The property that changes depends on the volumetric reaction:

• Acid-base: An acid is titrated with a base, or vice versa. The abrupt change is due to a slight excess of one reactant, producing a sudden change in pH.
• Redox: An oxidant is titrated with a reducing agent, or vice versa. The abrupt change is due to a slight excess of one reactant, leading to a sudden change in the cell potential formed by two electrodes.
• Precipitation: An ionic substance is titrated with a precipitating reagent. The abrupt change is due to an excess of the precipitating reagent, which causes a sharp decrease in