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

Conjugate Acid-Base Pairs

The CN⁻ ion is a base because it is capable of accepting a proton to form HCN, its conjugate acid:

CN⁻ + H₂O ⇌ HCN + OH⁻

The NH₄⁺ ion is an acid because it is capable of yielding a proton to form NH₃, its conjugate base:

NH₄⁺ + H₂O ⇌ NH₃ + H₃O⁺

The SO₄²⁻ ion is a base because it is capable of accepting a proton to form the HSO₄⁻ ion, its conjugate acid:

SO₄²⁻ + H₂O ⇌ HSO₄⁻ + OH⁻

Salt Hydrolysis and Solution pH

Potassium Chloride (KCl)

, is a salt that dissociates in aqueous solution leading to potassium ions (K +) and ions
chloride (Cl?). The chloride ion (Cl?) comes from a strong acid such as hydrochloric acid (HCl) and therefore it is
a weak conjugate base that is not

Classification of Chemical Reactions

Criteria for Classification

• Energy: Endothermic (absorbs heat, ΔH > 0) and Exothermic (releases heat, ΔH < 0).
• Kinetic: Reaction speed (Slow vs. Fast reactions).
• Direction: Reversible vs. Irreversible reactions.
• Nature of Reagents: Acid-base and Oxidation-reduction (Redox).

Factors Affecting Reaction Rates

• Concentration: Increasing concentration increases reaction rate.
• Temperature: Increasing temperature increases reaction rate.
• Surface Area: Increasing the contact surface between reactants increases reaction rate.

Reaction Directionality

A reaction proceeds until the limiting reagent is consumed in a closed system. Reversible reactions are characterized by occurring in both directions.

Properties of Acids

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,

Objective of the Flotation Process

The objective of the flotation line is a physicochemical process that allows the separation of sulfide minerals, such as copper sulfide and molybdenum minerals, from other species that share most of the original mineral. Flotation is performed using the pulp from the grinding stage, which has already incorporated the necessary reagents. The pulp is placed in containers called flotation cells, in which air bubbles are introduced while keeping the mixture under constant agitation so that particle contact is intense.

Concentration Cycles and Final Product

To obtain the product of the phase that requires flotation, the pulp passes through several cycles where bubbles generate a concentrate. For example, copper concentrate... Continue reading "Froth Flotation Process for Mineral Separation" »

The Nature of Matter

Matter is composed of atoms and empty space.

Molecules and crystals are associations of atoms, whether identical or different, always present in a fixed number or proportion.

Chemical elements are substances made of identical atoms.

Compounds are substances formed by atoms, molecules, or crystals of different types.

How Elements Appear in Nature

• Atomic: Atoms exist as isolated and widely separated particles.
• Molecular: Independent particles formed by identical atoms, usually two or three.
• Crystalline: Elements consisting of an endless number of identical atoms, closely packed and perfectly ordered.

How Compounds Appear in Nature

• Molecular: Comprised of independent particles formed by a fixed number of different atoms.
• Crystalline:

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" »

Chemical Bonding and Atomic Configurations

How the elements reach a noble gas configuration gives rise to three types of chemical bonds between atoms: ionic, covalent, and metallic.

• Chemical bonds: All the forces that hold together atoms when they form molecules or crystals, as well as the forces that hold together the molecules when present in a liquid or solid.
• Octet rule (Gilbert N. Lewis): Atoms are bonded with each other to achieve eight electrons in their valence level.

The Nature of Ionic Bonding

Ionic bonds form when atoms combine to reach the noble gas configuration. Atoms lose electrons to reach the noble gas configuration or gain electrons to reach it. One electronegative atom will tend to gain electrons and form a negative ion (anion)... Continue reading "Chemical Bonding Principles and Atomic Structures" »

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" »

Other Contributions to the New Worldview

Tycho Brahe: His astronomical observations were accurate enough in the long run to support heliocentric theses. His findings were inconsistent with the belief in Aristotelian spheres and the immutability of the cosmos. Brahe discovered a new star in the constellation Cassiopeia, destroying the notion that the supralunar world is free from generation and corruption; he also mapped the orbits of comets.

Johannes Kepler and Elliptical Orbits

Johannes Kepler, a disciple of Brahe, was an enthusiastic supporter of heliocentrism. He formulated a series of laws that moved away from the Aristotelian inheritance maintained by Copernicanism, specifically the circularity of orbits and the uniformity of their velocity.... Continue reading "Scientific Revolutions: Heliocentrism and Quantum Physics" »