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

Pure Substances and Mixtures

Substances are formed by the same particles (either atoms or molecules). They cannot be decomposed into other substances by simple procedures. These include elements and compounds.

Mixtures are formed by two or more substances. Mixtures, whether homogeneous or heterogeneous, can always be separated by physical means such as filtration, decantation, distillation, or chromatography.

Separation Methods

Separation methods are generally categorized based on the type of mixture:

• Mechanical Methods: Most useful for heterogeneous mixtures.
• Thermal Methods: Appropriate for homogeneous mixtures.

Mechanical Separation Methods

Sedimentation

Widely used in mining to separate ore from gangue by gravity.

Settling (Decantation)

Used when

... Continue reading "Chemical Substances, Mixtures, and Physical Separation Techniques" »

Biophysics Fundamentals

Biophysics is a branch of biology that studies the physical phenomena produced inside the cellular plasma.

1. Systems of Dispersions

A dispersion is a mixture of two substances in which one completely surrounds the other without settling. It consists of two phases:

• Dispersed phase: The solute.
• Dispersing phase: The solvent.

Classification of Dispersions

Dispersions are classified into three groups, including suspensions and emulsions.

Molecular Solutions

A solution or molecular dispersion is a mixture where both phases are closely linked to form a homogeneous, transparent substance.

Concentration of Solutions

Solutions are categorized by their solute concentration:

• Saturated: Contains the maximum amount of solute possible to dissolve.

... Continue reading "Biophysics Fundamentals: Solutions, Diffusion, and Osmosis" »

Fundamental Particle Properties

• Mass of Electron ($m_e$): $9.109534 \times 10^{-31}$ kg
• Charge of Electron ($q_e$): $-1.602189 \times 10^{-19}$ C
• Mass of Proton ($m_p$): $1.672649 \times 10^{-27}$ kg
• Charge of Proton ($q_p$): $1.602189 \times 10^{-19}$ C
• Mass of Neutron ($m_n$): $1.674954 \times 10^{-27}$ kg

Rays/channels are formed by positively charged particles. The relationship between charge and mass varies according to the gas used in the tube.

Quantum Numbers and Orbitals

Quantum numbers describe the state of an electron:

• Principal Quantum Number ($n$): Energy level
• Orbital Angular Momentum ($l$): Orbital shape (ranges from 0 to $n-1$)
• Magnetic Quantum Number ($m_l$): Orbital orientation
• Spin Quantum Number ($m_s$): Electron spin ($\pm 1/2$)

The... Continue reading "Atomic Structure: Particles, Orbitals, and Quantum Models" »

Reflux Constant and Steam Flow Dynamics

Reduced heating reflux constant: The steam flow rate increases with respect to the liquid, which leads to: a change in the cutoff of the load (heavier products in the head and higher flow rates), a lighter and smaller product flow background, and increased column temperatures.

If steam flow increases: Increasing the steam flow with respect to the liquid causes a heavy component transfer to the head and rising temperatures throughout the column.

Lentil Charts and XY Balance

Lentil chart: This represents the possible boiling collection ranges for different mixtures.

XY: This represents the balance between liquid and vapor at a given pressure.

ASTM Curves and Quality Metrics

ASTM Curve: Used to determine the quality... Continue reading "Distillation Column Performance and Separation Metrics" »

Gas Laws and Constant Variables

Constant Temperature: Boyle's Law

If the temperature remains constant, increasing the pressure on a gas decreases the volume it occupies. This occurs because the number of collisions per unit surface area increases.

Constant Pressure: Charles's Law

If the pressure on a gas is constant, a rise in temperature causes an increase in the volume it occupies. This is due to the particles having higher kinetic energy and therefore moving faster, causing more frequent collisions.

Constant Volume: Gay-Lussac's Law

If the volume occupied by a gas remains constant, an increase in temperature causes an increase in the pressure of the gas. This is because increasing the temperature increases the kinetic energy of the particles,... Continue reading "Gas Laws and States of Matter Fundamentals" »

Biophysics II

Colloids

Colloids are suspensions of very small particles (micelles), even much larger than the dispersed molecules within a liquid. They are also called pseudo-solutions or colloidal solutions.

State of Sol and Gel

Protoplasmic colloids undergo sol-gel processing, also called reversal or phase change. Colloids present an intermediate state between solid, liquid, and gas. States in the protoplasm of sol and gel usually alternate due to changes in concentration. The most important sols in biology are protein dispersions in water.

Types of Colloids According to the Physical State of the Phases

The dispersant phase can be a solid, liquid, or gas, just as the dispersed phase may be liquid, solid, or gaseous. The passage from a sol to a... Continue reading "Biophysics II: Colloids, Properties, and States" »

Properties of Acids

• Solutions often have a sour taste.
• They attack marble (CaCO₃) and other calcareous rocks.
• Metals react with acids, evolving hydrogen gas.
• Concentrated solutions destroy organic matter.
• They conduct electric current.
• Neutralize bases.
• Produce salts with bases.
• Change the color of acid-base indicators to red.

Properties of Bases

• Solutions often have a bitter taste.
• React with fats to form soaps, producing a soapy feel on skin.
• Generate insoluble solids with certain metals.
• Concentrated solutions destroy organic matter.
• They conduct electric current.
• Neutralize acids.
• Produce salts with acids.
• Change the color of acid-base indicators to blue.

Acid-Base Theories

Arrhenius Theory of Ionic Dissociation

In 1884, Svante Arrhenius (1859-1927) postulated,... Continue reading "Acids and Bases: Fundamental Properties, Theories, and pH Measurement" »

Methods of Water Purification

3. Ultraviolet (UV) Treatment

This method uses the appropriate wavelength to eliminate microorganisms and pathogens in water. UV light is more energetic than visible light and has a shorter wavelength. It is utilized for wastewater treatment with biological loads, irrigation water, and drinking water purification.

4. Copper-Silver Ionization

Small amounts of copper and silver are used to destroy microorganisms. It is applied in cooling towers, boilers, and similar systems. Its advantages include:

• Does not disrupt pH levels
• Easy to install
• Simple water recovery in case of loss
• Low maintenance costs

5. Water Softening

Hard water can cause lime deposition, fouling, and increases the consumption of soaps and detergents while... Continue reading "Advanced Water Purification and Demineralization Techniques" »

1. Decomposition Reactions

The scheme of a decomposition reaction is: A → B + C + ...

Decomposition reactions are those in which a substance is transformed into simpler ones due to an energy intake that can be performed in two ways:

• Thermal decomposition: Heat energy is supplied.

2Ag₂O → 4Ag + O₂

Electrolytic Decomposition: The energy provided is electric current.

CaCl₂ → Ca + Cl₂

2. Synthesis Reactions

The scheme of a synthesis reaction is: A + B + ... → C

These are reactions where two or more simple substances, elements, or compounds react to give a single compound.

3. Substitution Reactions

The scheme of a substitution reaction is: A + BC → AC + B

These are reactions in which an element of a reagent is replaced or exchanged for an element... Continue reading "Chemical Reactions: Types and Characteristics" »

Mass Transfer Operations

• Absorption: The separation of components of a gas mixture using a liquid that dissolves specific components.
• Distillation: Separating the components of a liquid mixture by vaporization and partial condensation of steam. This can be simple distillation or rectification (with reflux).
• Extraction: Separation of the components of a mixture through a solvent that is immiscible with it. This may be solid-solid or liquid-liquid extraction.
• Ion-Exchange: Chemical reactions between ions in a solution and a solid phase that is insoluble in the solution and placed in contact with it.
• Adsorption: The separation of components of a liquid or gaseous mixture through a solid surface.
• Electrodialysis: Separation using ion-exchange membranes

... Continue reading "Unit Operations in Chemical Engineering" »