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

Fundamentals of Biochemistry

Energy is essential for all biological processes. All atoms contain energy, and they are joined together by chemical bonds, which are crucial for life. We obtain our energy from food, converting it into chemical energy that can be stored and utilized, as opposed to other forms of energy like light and heat that cannot be retained.

Thermodynamics Principles

• First Law: Energy is neither created nor destroyed; it is only transformed from one form to another.
• Second Law: In every energy transmission, some energy is lost, typically as heat, leading to an increase in entropy.

Atomic Structure

The basic units of matter are atoms, composed of three fundamental subatomic particles: neutrons (neutral charge), protons (positive... Continue reading "Biochemical Foundations: Energy, Atoms, and Chemical Bonds" »

The Green Revolution

The Green Revolution refers to the significant increase in agricultural productivity achieved through the use of DDT and other pesticides, fertilizers, irrigation, and mechanization.

Overfishing

Overfishing occurs when tons of fish are caught, and fish populations are unable to reproduce quickly enough to compensate.

Sustainable Forestry in Finland

Finland has developed a science and practice of forest conservation and exploitation.

Excessive CO2 Consumption

Excessive consumption of CO2 has led to imbalances, and the effects of these imbalances are well-known. The extremely rapid increase in atmospheric CO2 concentration is often called the "hockey stick" due to its shape. This increase is primarily caused by the use of fossil... Continue reading "Environmental Impacts and Sustainable Energy Sources" »

Principal Components of Iron-Carbon Alloys

The main components of iron-carbon alloys include:

• Perlite: Thin films formed with ferrite (light gray) and cementite (dark gray). Carbon content is 0.89%. Ferrite is softer, while cementite is harder.
• Ferrite: Almost pure iron, very soft, ductile, and magnetic. Its structure is cubic.
• Cementite: Located on the right side of the eutectoid point due to its carbon composition (Fe3C). It is the hardest and most fragile constituent of steel.
• Austenite
• Martensite
• Ledeburite: Consisting of cementite and austenite.

Thermal Treatments for Steel

Thermal treatments modify the properties of steel:

• Tempering: Increases hardness, toughness, and yield strength, but also increases fragility. Methods include immersion in water,

Organic Reactions

Halogenation Substitution of Alkanes

CH₄ + Cl₂ → CH₃Cl + HCl

Obtaining Alcohol from Halogenated Alkanes

CH₃-CH₂-CH₂-CH₂Cl + KOH → CH₃-CH₂-CH₂OH + KCl

Addition Reactions to Double and Triple Bonds

Hydrogenation

Hydrogen is added to alkenes and alkynes to give alkanes in the presence of a metal catalyst.

CH₃-CH=CH-CH₃ + H₂ → CH₃-CH₂-CH₂-CH₃

Halogenation

Alkenes and alkynes react with halogens to give halogenated compounds.

CH₃-CH=CH₂ + Br₂ → CH₃-CHBr-CH₂Br

Adding Hydracids

Acid hydrogen is added to the carbon with more hydrogens (Markovnikov's rule).

CH₂=CH₂ + HI → CH₃CH₂I

Water Addition

Water is added to alkenes in the presence of acid and also follows Markovnikov's rule.

Voltaic Battery

A voltaic battery is a device that allows an... Continue reading "Understanding Organic Reactions, Voltaic Cells, and Salt Hydrolysis" »

Water Hardness

Hard water is water that contains appreciable amounts of dissolved calcium and magnesium compounds. These compounds form insoluble precipitates with soap. Ion exchangers are used to remove the hardness.

Temporary Hardness

Temporary hardness is caused by the presence of calcium and magnesium bicarbonates. It can be eliminated by heating the water to precipitate the calcium carbonate:

Ca(HCO₃)₂ → CaCO₃↓ + CO₂ + H₂O

Permanent Hardness

Permanent hardness refers to the remaining calcium and magnesium salts (not bicarbonates). It requires the addition of chemicals for removal, for example:

Na₂CO₃ + CaCl₂ → CaCO₃↓ + 2NaCl

Water Pollution

Thermal Pollution

Heat, in general, is not considered a contaminant, but its effects on water can... Continue reading "Water Hardness, Pollution, Cleaners, and Sampling" »

Selectivity in Chemical Analysis

A reaction used in chemical analysis is selective when the reaction is characteristic of few substances, showing a preference for some of these. When the reaction is carried out only on a particular substance, it is specific.

Limit of Detection (LOD)

Refers to the minimum amount of a substance that can be detected in a trial.

Sensitivity of Analytical Methods

The ability of a method to discriminate a change in concentration caused by a variation in the measurement of the analytical signal.

Qualitative vs. Quantitative Analysis

The science that studies the principles and techniques of chemical analysis. It is divided into:

• Qualitative analysis: Its purpose is the identification of the constituents of a sample (organic

Key Discoveries in Atomic Theory

Thomson's Discovery of Electrons

J.J. Thomson demonstrated that atoms contain tiny, negatively charged particles called electrons. He showed that atoms could lose electrons, suggesting a static atomic model.

Rutherford's Atomic Model

Ernest Rutherford established that atoms are mostly empty space. He proposed that a small, dense region, which he named the nucleus, resides at the atom's center. This nucleus contains protons and, as Rutherford suspected, neutrons. In his model, the number of protons equals the number of electrons, with the latter orbiting the nucleus in circular paths.

The Atom as a Planetary System

The Rutherford model is analogous to a planetary system because the nucleus represents the sun, and the... Continue reading "Atomic Structure and the Periodic Table" »

The Krebs Cycle

The Krebs cycle, also known as the Citric Acid Cycle, is an amphibolic pathway because:

• It facilitates the degradation of Acetyl-CoA.
• Its intermediate compounds serve as precursors for other synthetic processes.

Stages of the Krebs Cycle

The cycle is divided into the following stages:

1. Formation of Citric Acid

   Citric acid is formed from oxaloacetic acid and Acetyl-CoA.

   • Modifications: Oxaloacetic acid + Acetyl-CoA → Citric acid
   • Inputs/Outputs: Enters H₂O and Acetyl-CoA

2. Isomerization of Citric Acid to Isocitric Acid

   • Modifications: Citric acid → Isocitric acid
   • Inputs/Outputs: None

3. Oxidation of Isocitric Acid

   Isocitric acid is oxidized, reducing NAD⁺ to NADH, forming alpha-ketoglutarate, and releasing CO₂.

   • Modifications: Isocitric acid →

Defrosting is essential in refrigeration systems to remove ice accumulation on evaporators, which reduces efficiency and cooling capacity.

Natural Defrosting

This method is typically used in refrigerated spaces operating above +2°C. It involves stopping the refrigeration system (compressor and fans) for a period, allowing the warmer ambient air within the refrigerated space to melt the ice accumulated on the evaporator.

In low-temperature facilities for freezing and storage of frozen products, based on forced-air evaporators, it becomes necessary to create additional heat for defrosting to melt the ice.

Water Spray Defrosting

This method involves spraying water under pressure onto the ice accumulated on the evaporator. The water melts the ice and... Continue reading "Refrigeration Defrost Methods" »

Hemoglobin Iron Environment and Geometry

The iron ion (Fe) in Hemoglobin (Hb) is in a square planar environment, bonded to four nitrogen (N) atoms of the porphyrin ring. The fifth coordination position is bound to a nitrogen atom from a histidine residue (perpendicular to the plane), and the sixth position binds O₂ in oxyhemoglobin. When oxygenated, the coordination geometry around the iron is essentially octahedral. In contrast, deoxygenated Hb has a five-coordinate, square pyramidal geometry, as the sixth position is vacant.

Role of Magnesium and Calcium Competition

Magnesium (Mg) is extremely important. It plays a role related to the Na⁺/K⁺ pump; the interior of the cell requires large amounts of K⁺ and low amounts of Na⁺. Mg facilitates the... Continue reading "Iron and Copper Roles in Biological Oxygen Transport" »