Notes, abstracts, papers, exams and problems of Chemistry

Structure of DNA and RNA

Understandings:

The nucleic acids DNA and RNA are polymers of nucleotides.

• Nucleotides are the monomers of the polymer DNA.
• DNA nucleotides are made up of 3 components: a phosphate group (PO₄^-3), a pentose sugar, and a nitrogenous base.
• The phosphate, sugar, and base are linked by covalent bonds.
• In DNA and RNA, each nucleotide is linked to the next nucleotide between the phosphate of one and the pentose sugar of the other nucleotide.

DNA differs from RNA in the number of strands present, the base composition, and the type of pentose.

Wastewater Treatment

Sludge Density Index (SDI)

The weight in grams of one mL of sludge after settling for 30 minutes. SDI = 100/SVI.

Process Design Examples

• Complete Mix Activated Sludge (CMAS): Air is blown into the tank to keep the waste mixed with the organisms and to add oxygen to the water. This process removes soluble suspended solids (SS) and ammonia by exposing the waste to organisms.
• Sequencing Batch Reactor (SBR): This reactor operates under non-steady state conditions in a batch mode with aeration and sludge settlement occurring in the same tank. The SBR tank carries out the functions of equalization, aeration, and sedimentation in a time sequence.
• Staged Nitrification Process: Offers greater treatment efficiency and capacity than a single

Metals, Bonding, and Extraction: Key Concepts

Attractive forces in a metallic structure arise because positive ions and electrons attract each other.

High Melting Points

Why does X have a high melting point? Due to its giant covalent structure, a lot of energy is needed to break the strong covalent bonds.

Lattice Structure of Metals

Why do metals have a lattice structure? The atoms in a pure metal are arranged in closely packed layers, which makes them strong.

Alloys

Alloy: A mixture of a metal with at least one other element.

Isotopes

Isotope: An atom with a different number of neutrons.

• The more reactive the metal, the more likely it is to corrode from oxygen and water.

Ores

Ore: A rock that contains enough metal to make mining and extraction economical.... Continue reading "Metals, Bonding, and Extraction: Key Concepts Explained" »

Carbon's Versatility

Carbon is a versatile atom due to its ability to form four covalent bonds with other atoms, including other carbon atoms. This allows carbon to create a wide variety of organic molecules with diverse structures and functions.

Definitions:

• Organic Compound: A compound containing carbon that is typically found in living organisms.
• Hydrocarbon: An organic compound consisting of only carbon and hydrogen atoms.
• Macromolecule: A large molecule formed by the joining of smaller repeating units (monomers). Examples include proteins, carbohydrates, and nucleic acids.

Dehydration and Hydrolysis Reactions

Dehydration Reaction:

A dehydration reaction is a chemical reaction where water is removed from the reactants to form a larger molecule.... Continue reading "Organic Molecules: Structure and Function" »

Electronegativity

Measure of the tendency of an atom to attract bonding pair of electrons.

Cation

Ion that has a positive charge.

Ionic Bond

Chemical bond formed between two ions with opposite charge.

Anion

Ion that has a negative charge.

Chemical Bond

Electrical attraction between nuclei and valence electrons that binds atoms together.

Covalent Bond

Bond formed when atoms share one or more pairs of electrons.

Non Polar Bond

Type of chemical bond where two atoms share a pair of electrons with each other.

Polar

Uneven distribution of charge.

Polar Bond

Type of chemical bond where a pair of electrons is unequally shared between two atoms.

Molecule

Neutral group of atoms that are held together by covalent bonds.

Molecular Compound

Chemical compound whose simplest... Continue reading "Chemical Bonding and Organic Chemistry" »

Properties of Metals:

Shiny, lustrous, can be polished, strong, and solid.

Nonmetals:

Dull, not lustrous, cannot be polished, weak, half are gases.

18 Families or Groups, 18 Periods:

Elements in the same group have common characteristics. Horizontal is period, vertical is family or group.

Periodic Law:

The PT is organized by atomic number Z. Elements with similar properties are in the same family.

Properties of Metalloids:

Have characteristics of metals and nonmetals. Located between metals and nonmetals.

Johann Dobereiner (1829):

Classified elements into groups of three, called triads.

John Newlands (1838-1898):

Law of Octaves (1863) suggested arranging elements in octaves.

Dmitri Mendeleev (1834-1907):

Published a table of elements organized by increasing... Continue reading "Evolution of the Periodic Table: From Triads to Actinides" »

Mixtures and Compounds

A mixture is a material system made up of two or more different substances which are mixed but not combined chemically.

Types of Mixtures

• Heterogeneous: The components are visibly diverse.
• Homogeneous: The components are uniformly distributed, appearing as a single substance.

Basic Chemical Concepts

• Phase: A physically distinct form of matter, such as a solid, liquid, or gas.
• Element: A substance that is made up of only one type of atom.

Changes of State

• Melting Point: The temperature at which a solid melts. The particles gain energy, vibrate faster, and eventually move around, becoming a liquid.
• Boiling Point: The temperature at which a liquid boils. The particles gain energy, move faster, break free, and become a gas.

Tests for

Biotic and Abiotic Factors in an Ecosystem

• Chemistry: The study of matter.
• Matter: Any substance that has mass and takes up space.
• Energy: The capacity of a physical system to do work.
• Ecosystem: All of the living things in a given area.
• Biotic: Living organisms (e.g., flowers, plants, bacteria).
• Abiotic: Non-living organisms (e.g., water, soil, air, light, wind).

States of Matter

• Solids: More dense, particles are very close, molecules only vibrate, cannot flow, defined shape, defined volume, not compressible.
• Liquids: Dense, particles are close, molecules have random flow, can flow, adaptable shape, defined volume, very little compressible.
• Gas: Less dense, particles are separated, molecules have a random, fast, and free movement, can flow, no shape,

HOW DO ATOMS BEHAVE DURING A CHEMICAL REACTION?

Chemical reactions occur when bonds between atoms break and new bonds form, creating a new arrangement of atoms and at least one new substance. Observable changes, such as temperature fluctuations, color changes, gas formation, new solids, and odors, accompany these reactions.

Conservation in Chemical Reactions

Besides energy, mass is also conserved during chemical reactions. Lavoisier's experiment disproving the "phlogiston theory" led to the development of the "law of conservation of mass," which states that matter cannot be created or destroyed in a chemical reaction. Balanced chemical equations represent this law.

Energy and Reactions

Energy is required to initiate reactions. Simply mixing chemicals... Continue reading "Understanding Chemical Reactions: From Atoms to Acid Rain" »