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

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" »

Early Atomic Theories and Discoveries

Early Theories

• Greek philosophers believed everything was made by combining a few simple, undecomposable substances: the four elements: water, air, fire, and earth.

Dalton's Atomic Theory

• Matter is made up of extremely small, indivisible, and indestructible atoms.
• All atoms of a specific chemical element are identical but differ from atoms of other elements.
• Chemical compounds are formed by the union of atoms of different elements in the same, fixed proportions.

Fundamental Definitions

• Chemical Element: A substance that cannot be decomposed into simpler substances.
• Compound: A substance that can be decomposed into simpler substances.
• Electrolysis: A process used to decompose a pure substance using an electrical current.

Historical Discoveries and Early Particle Evidence

Faraday; Stoney (coined the name electron in connection with electricity); cathode-ray tube observations (CRT); Thomson (charge-to-mass ratio of the electron); Millikan (electron charge); Goldstein (canal rays); Aston (mass spectrometer).

Atomic Models and Development

Atomic models—development and key ideas:

• Thomson: plum-pudding model; early ideas from scattering and particulate experiments.
• Rutherford: nuclear atom obtained from alpha-particle scattering; nucleus-centered model. (Reference: neutron discovery by Chadwick.)
• Bohr: combines Rutherford's nuclear atom and Planck's quantum concepts — energy is absorbed or emitted in quanta; discrete postulated orbits; quantized angular momentum

ionophore: a pesomolecular compounds ranging from 500-2000, which have a hydrophobic outer surface which is soluble in lipids, and a hydrophilic interior to which the ion binds. There is little evidence that ionophores are physiological constituents of energy-transducing membranes. Through two mechanisms can function as mobile carriers and as trainers of channels or conduits. The mobile carriers can diffuse through the membrane lipid matrix and catalyze the transport of a few thousand ions per second across the membrane. They can show a high selectivity towards the different ions, heavy work through synthetic membranes, but are affected by the state of membrane fluidity. Example, valinomycin is highly selective for potassium cation. By contrast,... Continue reading "Ionophores, Chemiosmosis, and Chemical Equilibrium" »

Photosynthesis: Anabolic Process Converting Inorganic to Organic

Photosynthesis converts inorganic matter into organic using solar light. Sunlight's energy is converted into chemical energy within organic compounds. During photosynthesis, oxygen (O2) is released into the atmosphere. The overall process can be summarized as: CO2 + H2O + Light -> Organic Matter + O2.

However, this simplified equation doesn't reflect the actual process. The oxygen released comes from water, not carbon dioxide. Glucose formation and oxygen release are independent processes.

Light Phase (Hill Reaction)

The light phase occurs in the thylakoids, where photosystems are located. It requires light and produces:

• Reducing power: NADPH + H+
• Energy: ATP (produced using sunlight)

Group 15 Elements (Nitrogen Family)

The nitrogen family (Group 15) includes Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb), and Bismuth (Bi).

Physical Properties

• Allotropy: Phosphorus, Arsenic, and Antimony exhibit allotropy.
• Phosphorus: White phosphorus is highly active, while other forms are relatively inactive.

Oxides of Nitrogen

• N₂O: Nitrous oxide (laughing gas).
• NO: Nitric oxide (paramagnetic).
• NO₂: Nitrogen dioxide.
• N₂O₄: Dinitrogen tetroxide (diamagnetic).

Ammonia and Nitric Acid

Ammonia (NH₃) reacts with water to form ammonium hydroxide (NH₄OH). Nitric acid (HNO₃) is produced via the Ostwald process using a platinum catalyst.

Nitric Acid Properties

• Commercial HNO₃ (~15M) often appears yellow due to dissolved nitrogen oxides.
• It acts as

Science Concepts: Physical and Chemical Sciences

SCIENCE is a wealth of knowledge about the world obtained through observation, experimentation, and reasoning. Laws are deduced from verifiable theories that are elaborated from these processes.

Physical and Chemical Sciences

PHYSICAL-q is the science that studies any change that does not alter the material nature of matter. QUIMICA-is is the science that studies the composition, combinations, and transformations of substances that affect their nature.

General Properties

General Properties are values that serve to identify a substance; for example, volume and temperature are properties used to describe matter.

Property Features

THE PROPERTY FEATURES are the characteristic values for each substance.... Continue reading "Science Concepts: Physical & Chemical Properties, Measurement" »

Understanding Material Systems and Separation Techniques

Heterogeneous system material should appear uniform. Akella system material is presented uniformly. All points of the material system are separated for experimental study.

Decompose a compound using chemical procedures into simple substances. A simple substance is a pure substance that cannot be decomposed into other simpler substances by ordinary chemical procedures. A simple substance is formed by a single type of element. A compound is a pure substance formed by two elements combined in fixed, homogeneous proportions.

Dissolving creates a blend made uniform by two pure substances in variable proportions.

Simple Distillation

Used to separate a dissolving liquid formed by two points with... Continue reading "Understanding Heterogeneous and Homogeneous Systems" »

Propiedades y Ensayos de los Metales

Elementos metálicos puros

No se pueden emplear para la fabricación de piezas. Las aleaciones (dos o más elementos) mejoran sus propiedades.

Propiedades de los metales

• Dureza: Oposición al rayado o penetración. Da idea de la resistencia de un material a la deformación permanente.
• Elasticidad: Capacidad de recuperación al cesar la fuerza que los deforma. El límite elástico es la fuerza máxima de deformación.
• Tenacidad: Propiedad que tienen los metales de no romperse. Se opone a la rotura y absorbe la fuerza; da idea de la capacidad que tiene un metal de absorber energía antes de romperse.
• Fragilidad: Facilidad de rotura bajo la acción del choque.
• Fatiga: Resistencia que tiene un material de no romperse

Metals: Properties, Processing, and Applications

Copper

Classification: Density > 5. Danger 5-2, Ultralight < 2.

Advantages: Electrical and thermal conductivity, oxidation and corrosion resistance, low melting point.

Disadvantages: Lower mechanical resistance, more difficult and expensive to obtain.

Sources:

• Native copper: (Poor mineral, not usually found)
• Sulfides: Chalcopyrite and chalcocite
• Oxides: Malachite and cuprite

Characteristics: Reddish, relatively soft, high electrical conductivity, very ductile and malleable, moderate resistance to acids.

Obtaining Process:

• Wet process: Copper < 10%. Diluted sulfuric acid is added to an electrolytic bath.
• Dry process: Copper > 10%. Crushing, grinding, mineral separation, and gangue by flotation