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

Nuclear Physics Fundamentals

The atomic nucleus is formed by nucleons (protons and neutrons). The atomic number (Z) defines the mass.

Nuclide Classifications

• Isotopes: Nuclides with the same number of protons but a distinct number of neutrons.
• Isobars: Nuclides with the same mass number (A) but a distinct number of protons and neutrons.
• Isotones: Nuclides with the same number of neutrons but a different number of protons.

Fundamental Forces of Nature

• Gravitational Force: Exerted between two particles with mass. It is always attractive and responsible for the existence of planets and stars. It is a weak, long-range interaction.
• Electromagnetic Force: Exerted between two electrically charged particles. It can be attractive or repulsive and is responsible

Matter: Core Properties, States, and Mixtures

Matter is anything that has mass and occupies volume. It is characterized by two types of properties:

Key Properties of Matter

• General properties: These are mass and volume.
• Specific properties: These are different in each material, so they serve to differentiate materials from each other and assign them different uses.

The Three States of Matter

Matter can occur in three states:

• Gas: A gas has no definite shape and spreads to fill its container. It can be compressed and expands greatly with temperature.
• Liquid: A liquid does not hold its own shape (it takes the shape of its container) but has a definite volume. It is not easily compressed and expands slightly with increasing temperature, although much

Acid–Base Theories

Arrhenius (1883)

Acid: A substance that yields H⁺ in aqueous solution. Base: A substance that in aqueous solution gives OH^-.

Limitations: substances with basic properties that do not contain hydroxyl ions (e.g., NH₃); limited to aqueous solutions. Free, isolated protons do not exist in water.

Brønsted–Lowry (1923)

Acid: A species that tends to donate an H⁺. Base: A species that tends to accept an H⁺.

Lewis (1923)

Acid: A species that can accept an electron pair. Base: A species that can donate an electron pair.

Buffer Solutions

1. Buffer (dissolution buffer)

Definition: Buffer solutions are solutions that maintain a nearly constant pH when small amounts of acid or base are added, or when diluted.

Composition: Significant amounts... Continue reading "Acid–Base Theories, Buffers, Indicators, Titrations & pKa List" »

Binary Compounds

Binary Oxygen Compounds (Oxides)

Systematic Nomenclature

• Prefixes (mono-, di-, tri-, tetra-...) + oxide (element symbol).
• e.g., N₂O₅: Dinitrogen pentoxide.

Stock Nomenclature

• Oxide of (element) + (valence of element in Roman numerals).
• e.g., N₂O₅: Nitrogen(V) oxide.

Binary Hydrogen Compounds (Hydrides)

Metal Hydrides (Hydrogen + Metal)

Systematic Nomenclature

• Prefixes (mono-, di-, tri-, tetra-...) + hydride of (metal).
• e.g., CrH₃: Chromium trihydride.

Stock Nomenclature

• Hydride of (metal) + (valence of metal in Roman numerals).
• e.g., CrH₃: Chromium(III) hydride.

Volatile Hydrides (Hydrogen + Semimetal)

Systematic Nomenclature

• Prefixes (mono-, di-, tri-, tetra-...) + hydride of (semimetal).
• e.g., PH₃: Phosphorus trihydride.

Common Names

• Ammonia

Condensation Polymers

Esterification Reaction: alcohol (OH) + carboxylic acid (COOH) = Ester (COO) + water (H₂O)
Amidation Reaction: amide (NH₂) + carboxylic acid (COOH) = amine + water

Any union of acid and amine produces water.

Natural Polymers:
Protein:
Composed of amino acids (aa). A-AAs are the only proteins involved in the process.
The amino acids are classified in four ways: acidic, basic, polar, and nonpolar.

Acid-Base Character of the Amino Acids:
Amino acids in pure form are solids that crystallize as hydrochlorides (the amino group is protonated). When dissolved in water, they behave as weak acids and bases, reaching a chemical equilibrium characterized by the acidity constant (pKa).

Cationic Form (aa¹⁺): The compound has a positive... Continue reading "Understanding Condensation Polymers and Protein Structures" »

Alkaline Metals (ns1)

Alkaline metals have an oxidation number of +1. Features: They are soft metallic elements and react easily, with a low ionization potential that facilitates chemical reactivity. Properties: They are strongly reducing because they are easily oxidized in contact with air. They react with water to form hydroxides.

Alkaline Earth Metals (ns2)

Alkaline earth metals have an oxidation number of +2. Characteristics: They are metallic elements with a greater potential than the previous group. They are not found free in nature but form compounds of an ionic type, except for the beryllium ion which is covalent. Chemically, they oxidize in the air because they are good reducing agents and react with water, giving off hydrogen and forming... Continue reading "Main Group Elements: Properties and Oxidation States" »

Acids and bases are utilized in volumetric analysis to determine the concentration of unknown substances. This document details two common acid-base titrations: determining ammonia concentration and calculating vinegar acidity.

Part 1: Ammonia Concentration Determination

The goal is to determine the amount of pure ammonia (NH₃) in a solution using an acid titration (valorization).

Titration Data and Dilution

• Initial Sample: 20 mL of concentrated ammonia solution.
• Dilution: The 20 mL sample was diluted to a final volume of 500 mL.
• Aliquot Titrated: 25 mL of the diluted solution was used.
• Titrant: 22.7 mL of 0.5 M HCl was required to reach the endpoint.

Calculation of Moles

The reaction is NH₃ + HCl → NH₄Cl (1:1 stoichiometry).

1. Calculate moles of... Continue reading "Chemical Titration Analysis: Ammonia and Vinegar Acidity" »

Formulation of Oxides

To formulate oxides, write the element symbol followed by the oxygen symbol, then exchange their valencies and simplify if possible.

• Traditional Naming: Uses specific suffixes based on valency: -ic for one valency; -ous (lower) and -ic (higher) for two; hypo-...-ous, -ous, and -ic for three; and per-...-ic for four.
• Systematic Nomenclature: Uses prefixes such as mono-, di-, tri-, tetra-, penta-, and hexa-.
• Stock Nomenclature: Uses the term "oxide" followed by the metal name and its valency in Roman numerals.

Examples:

• K₂O: Dipotassium monoxide / Potassium oxide
• N₂O₅: Dinitrogen pentoxide / Nitrogen oxide (V)

Hydrides

In hydrides, hydrogen acts with a valency of -1, and valencies are exchanged.

Examples:

• PbH₄: Lead(IV) tetrahydride

Stereoisomerism and Carbohydrate Structure

Asymmetric carbons occur when a radical is attached to four different groups, leading to stereoisomerism. Isomers are compounds with the same molecular formula but different chemical properties.

Monosaccharides and Cyclic Structures

Haworth projections represent monosaccharides where each carbon radical is positioned at the top or bottom of the plane. The ring is formed by a covalent bond joining an alcohol group with an aldehyde or ketone.

• Anomeric Carbon: A new asymmetric carbon that appears in monosaccharides when forming cyclic structures from aldehyde or ketone groups.
• Mutarotation: The change in the rotation values of plane-polarized light during the transition from one anomer to another.
• Fehling's

Osmosis, Buffers, Colloids, and Carbohydrates

Osmosis: Osmosis occurs when two solutions with different ionic concentrations are separated by a semipermeable membrane that allows water to pass through but restricts the passage of ions. There are three types of solutions: isotonic, hypertonic, and hypotonic.

Buffer Systems

In organisms, buffer systems are crucial for maintaining a stable pH in fluids. These systems prevent abrupt pH changes. Buffers are based on the properties of weak acids, which do not dissociate completely. Within a specific pH range, they act as proton donors and acceptors, maintaining a constant pH within certain limits. Certain salts and corresponding acids balance the pH. For example, the HCO-3/H2CO3 (bicarbonate buffer)... Continue reading "Osmosis, Buffers, Colloids, and Carbohydrates: A Concise Review" »