Notes, abstracts, papers, exams and problems of Chemistry

The Calvin Cycle

The Calvin cycle's objective is to fix carbon dioxide (CO2) using ribulose-1,5-bisphosphate. For every triose (3-carbon sugar), two are needed to form a glucose, requiring 3 ribulose and 3 CO2. A hexose (6-carbon sugar) requires 6 ribulose and 6 CO2.

Phases of the Calvin Cycle

1. Carbon Fixation: Ribulose-1,5-bisphosphate (5C) combines with CO2 to form a 6C compound. Enzyme: Ribulose bisphosphate carboxylase. This creates a highly unstable compound. Input: 1 CO2 per ribulose.
2. Reduction: The unstable 6C compound splits into two triose molecules (3C), specifically glyceraldehyde-3-phosphate. Input/Output: None.
3. Phosphorylation: Glyceraldehyde-3-phosphate is phosphorylated using ATP, transforming into 1,3-bisphosphoglycerate. Input: 1

Q: Explain in detail the interaction of hydrophobic or hydrophobic effect. Is it a chemical bond? Explain your answer. Discuss the importance of this phenomenon in the formation and stability of biological membranes.
Hydrophobic Effect: The tendency of nonpolar molecules to cluster in polar solvents like H₂O for energetic reasons. Nonpolar substances tend to associate with one another in aqueous solutions because this results in fewer water molecules being involved in the cage that surrounds them. This situation is thermodynamically favored as it leads to lower order due to fewer water molecules (i.e., the entropy is higher) compared to when each polar molecule is surrounded by individual water molecules.
It is a chemical bond since it is... Continue reading "Understanding Hydrophobic Effects and Stereoisomerism in Chemistry" »

Properties of Ionic, Covalent, and Metallic Substances

Ionic Substances

Thermal Stability: Ionic compounds are typically solid at room temperature and pressure due to strong electrostatic attractions between ions, resulting in high melting and boiling points. The greater the charge of the ions and the smaller the distance between them, the higher the melting and boiling points.

Solubility: Polar solvents can reduce the attractive forces between ions by interposing solvent molecules. Each ion becomes surrounded by solvent molecules (solvation). Solubility decreases with increasing charge of the ions. Therefore, substances containing Group IIA metals (alkaline earth metals) are generally less soluble than those formed by Group IA metals (alkali... Continue reading "Ionic, Covalent, and Metallic Substances: Properties Compared" »

Emission and Absorption Spectra

The elements emit energy in the form of electromagnetic radiation, but only at a few specific frequencies. Elements also absorb specific frequencies when illuminated with electromagnetic radiation.

The de Broglie Hypothesis

The de Broglie hypothesis expanded the dual behavior of radiation, suggesting that matter, especially electrons, also exhibits both particle and wave aspects. According to this hypothesis, the energy of both matter and radiation is related to the frequency (f) of the wave associated with their movement through the expression E = hf. Thus, the wavelength associated with a material particle or photon momentum is λ = h / p.

The Uncertainty Principle

The principle of indeterminacy, or uncertainty... Continue reading "Atomic Spectra, Radioactivity, and Nuclear Reactions" »

Concentration Changes During Assessment

During an assessment, there must be an abrupt change in some property of the reaction mixture at the equivalence point. The property that changes depends on the volumetric reaction:

• Acid-base: An acid is titrated with a base, or vice versa. The abrupt change is due to a slight excess of one reactant, producing a sudden change in pH.
• Redox: An oxidant is titrated with a reducing agent, or vice versa. The abrupt change is due to a slight excess of one reactant, leading to a sudden change in the cell potential formed by two electrodes.
• Precipitation: An ionic substance is titrated with a precipitating reagent. The abrupt change is due to an excess of the precipitating reagent, which causes a sharp decrease in

Understanding Chemical Reactions

Law of Conservation of Mass

In a chemical reaction, mass is conserved. This means that the total mass of the products obtained is equal to the total mass of the reactants that have reacted.

Law of Conservation of Mass

Law of Constant Proportions

The reagents involved in a chemical reaction always react in fixed proportions.

Example: If hydrogen and oxygen react to form water, 1 g of hydrogen always reacts per 8 g of oxygen, and that is always going to be the proportions necessary to form water. The proportions are:

And so on. If there is more of one of them, it will stay without reacting. If we put 4 g of hydrogen and 24 g of oxygen, only 3 g of hydrogen... Continue reading "Understanding Chemical Reactions: Mass Conservation & Constant Proportions" »

Science

Science is a vast enterprise involving human effort to acquire solid, ascertainable truth. It is seen as a series of actions designed to obtain verifiable facts and is synonymous with social activity.

Objectivity

Objectivity originates from the word "object," referring to what is being discussed or investigated. It means attempting to obtain knowledge that accords with the reality of the object, describing or explaining it as it is, not as we want it to be.

Rationale

Rationale refers to the use of reason in science to obtain essential results. Scientists work with concepts of reasoning rather than feelings, pictures, or impressions.

Systematic Approach

A systematic approach means being organized in searches and results. It concerns building... Continue reading "Understanding Scientific Principles: Objectivity, Systems, and Atoms" »

Firefighting Foams Characteristics

• Fluency and Sealing: Ensures quick and effective surface coverage, preventing fuel vapor escape.
• Heat Resistance: Maintains cooling properties under mechanical stress and heat.
• Durability: Resists heat, flames, and wind; regenerates if surface cracks occur.
• Contamination Resistance: Maintains a uniform bubble structure when exposed to liquid fuels.
• Thickness: Holds enough water to withstand contact with hot surfaces of non-liquid or solid fuel.
• Oxygen Separation: Physically separates oxygen from the air above the ignited fuel surface.
• Heat Absorption: Absorbs heat from the fuel and adjacent solid surfaces.
• Radiation Prevention: Prevents heat transmission from flames via radiation.

Dry Columns: Function and Operation

A... Continue reading "Firefighting Foams, Dry Columns, and Fire Types" »

Error Variables in Micrometers

Error variables are errors that vary according to the dimension being measured. Such errors mainly come from variations in the passage of the screw micrometer. It is not possible to correct a variable error in the micrometer, but the error can be known if the tool has it.

Other Types of Micrometers

By suppressing, eliminating, or modifying the body of a standard micrometer, variants can be obtained. Different models are set up to fit a wide variety of measurements, including:

• Interior micrometer
• Micrometers with three inner supports
• Interior micrometers for small diameters
• Depth micrometers
• Special micrometers

The Melting Point

The melting point is a physical constant used in organic machines, but it can be defined as the... Continue reading "Understanding Micrometers, Melting Points, and Fluid Properties" »

Periodic Table of Elements

7s 7p
6s 6p 6d
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s

Elements are sorted by atomic number and grouped by chemical and physical properties, with 18 groups and 7 periods.

Group

A group consists of elements that have a similar electron configuration at the highest energy level. They have the same number of electrons in the same type of sub-levels, although at different energy levels. The chemical characteristics are similar and depend on the outermost electrons of the atoms. There are 18 groups.

Period

A period comprises all elements whose maximum energy level is the same. There are 7 periods: the 1st has 2 elements, the 2nd and 3rd have 8 elements, the 4th and 5th have 18 elements, and the 6th has 32 elements.

Periodic