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

Carbon and the Carbon Cycle

Carbon is a nonmetallic element, relatively scarce in the Earth's crust and atmosphere. It is a fundamental component of living matter, both plant and animal. The carbon cycle provides the atmosphere with carbon dioxide. Carbon dioxide allows plants, through photosynthesis, to synthesize their living matter. This plant material is assimilated by animals to form their own living matter. The carbon returns to the atmosphere as carbon dioxide through the respiration of living organisms, the decomposition of organic matter, and the combustion of fossil fuels formed from these materials.

Properties of Carbon Compounds

Carbon compounds tend to react relatively slowly compared with many ionic substances. Their melting and... Continue reading "Carbon and Hydrocarbons: Properties, Uses & Reactions" »

Fundamentals of Metal Heat Treatment

1. Why are metals heat treated?

Metals are heat treated to obtain specific properties, such as increased strength, improved hardness, or enhanced toughness.

2. Defining Allotropic and Non-Allotropic Materials

This distinction applies to both ferrous and nonferrous materials.

• Allotropic Materials: These materials undergo a reversible change in their atomic structure (lattice network) when subjected to temperature variations. This change in crystal structure is known as an allotropic transformation.
• Non-Allotropic Materials: These materials do not change their lattice structure regardless of temperature changes within the relevant processing range.

3. Most Important Heat Treatment for Hardening Steels

The most important... Continue reading "Fundamentals of Metal Heat Treatment and Material Properties" »

Metallic Material Classification

Metallic materials are classified in several ways:

• By chemical composition (e.g., steel or bronze).
• By use (e.g., light-alloy steel, light alloys).
• By manufacturing process (e.g., sintered materials).
• By main applications (e.g., for ships, plates).

Forms of Iron Materials

Iron can exist in various forms, including:

• Forged iron
• Cast iron
• Steel
• Conglomerate iron

Non-Ferrous Material Classification

Non-ferrous materials are classified into:

• Heavy Alloys: Copper, lead, zinc.
• Light Alloys: Aluminum, titanium.
• Ultra-Light Alloys: Magnesium, beryllium.

The Catalan Forging Process

The Catalan forging process utilized a small furnace or fireplace where wood or charcoal combustion was alternated with iron ore. Combustion, enhanced by air... Continue reading "Metallic Materials: Classification, Iron, Steel, and Casting" »

Normality (N)

Normality expresses the equivalent number of grams of solute present in one liter of solution.

Calculating the Equivalent Gram (Eq)

The equivalent gram is crucial for calculating normality. Its determination depends on the nature of the substance:

Equivalent Gram for Acids

To determine the equivalent gram of an acid, divide the gram molecular mass by the number of replaceable hydrogen atoms (H+).

Equivalent Gram for Bases or Hydroxides

To determine the gram equivalent of a base or hydroxide, divide the gram molecular mass by the number of hydroxyl groups (OH-) present.

Equivalent Gram for Salts

To determine the equivalent gram of a salt, divide the gram molecular mass by the total positive valence of the metal cation.

Molality (m)

Molality... Continue reading "Essential Definitions in Solution Chemistry and Titration" »

Zinc Concentrate Roasting Process: 850 T/day Capacity

Blende-Roasting Furnace and Heat Recovery Steam Generator

This includes the furnace that carries out the oxidation of ZnS, the heat recovery steam generator for cooling the gas, and the partial removal of solids carried by the gases.

Treatment Water for Steam-Water Circuit

This is the demineralized process water. This water will be used in the heat recovery boiler and furnace beams, which form part of the same circuit.

Purification of Gases from Roasting

The functions of the gas produced are to eliminate impurities and reduce the gas temperature for treatment.

Contact and Absorption

This is the transformation of SO₂ into sulfuric acid for reuse in marketing or the leaching stage.

Feedstock and Products

This... Continue reading "Zinc Concentrate Roasting Process in a Fluidized Bed Furnace" »

Physical and Chemical Changes in Matter

A physical change is a transformation that does not vary the nature of matter. Before and after the change, the matter is represented by the same chemical formula. A chemical change is a transformation in which the nature of matter varies. Before the change, the substance is represented by one chemical formula, and afterwards, by a different formula.

The Collision Theory of Reactions

Collision theory: Chemical reactions occur when molecules of reactants collide and break. Atoms that have been released are rearranged to form new molecules.

Measurement of Mass: The Mole

The mole: A mole of atoms is the amount of a chemical element that is equivalent to its atomic mass in grams. In the SI system, the mole is... Continue reading "Chemical Reactions and the Mole Concept" »

Ferrous Metals Classification

Based on Carbon Content

• Irons (0.01% to 0.03% C): White, difficult to obtain, with few industrial applications.
• Steels (0.03% to 1.76% C): Iron-carbon alloys that may contain other elements.
• Cast Irons (1.76% to 6.67% C): Iron-carbon alloys that may have other elements.
• Graphites (more than 6.67% C): Very fragile with no industrial applications.

Types of Cast Iron

Regular Cast Iron

• White Cast Iron: Very hard and brittle, used to make malleable iron.
• Gray Cast Iron: Used in malleable castings.
• Mottled Cast Iron: An intermediate between white and gray cast iron.

Alloyed Cast Iron

Contains iron, carbon, and other elements to improve its chemical properties.

Special Cast Iron

• Whiteheart Malleable Iron: A piece is molded in white

Chlorides

Chlorine, as an element, has a huge tendency to form the chloride ion (Cl^-, a chlorine atom with a negative charge). This ion, in turn, will tend to form salts with other positively charged elements or cations (Na⁺ sodium, K⁺ potassium, Mg²⁺ magnesium, etc.). The chloride ion is one of the main inorganic anions in natural water and wastewater. The chloride content of water is variable and is mainly due to the nature of the terrain traversed. Typically, the chloride ion content of natural waters is less than 50 mg/L. In drinking water, the salt produced by the Cl^- is variable and depends on the water chemistry.

Chlorite and Chlorate

These are salts derived from chloric acid and chlorous acid. These compounds tend to form chlorine gas,... Continue reading "Chloride: Properties, Uses, and Health Effects" »

Ranking Elements

The first classification of chemical elements was based on their chemical and physical properties, dividing them into two large groups: metals and non-metals.

• The first classification was done by J.W. Döbereiner. He observed a link between the atomic mass and properties of elements such as barium, calcium, and strontium. He arranged 40 elements in a line, one after another, by their mass.
• John Newlands arranged the elements by atomic mass, from the lowest to the highest, in columns. This is now called the Law of Octaves.
• D.I. Mendeleev arranged the elements by atomic mass. As a result of this work, the periodic law of elements was discovered in 1869.

Forces Between Molecules

These are listed from weakest to strongest:

1. Dispersion

Atomic Structure: Models and Definitions

The Plum Pudding Model

The Plum Pudding Model considers the atom as a ball of positive charge with electrons (negative charge) embedded.

The Rutherford Model

Rutherford's Bombardment Experiment

Rutherford tested the Rutherford Model by bombarding metal foil atoms with alpha particles (projectiles harder than atoms).

Experimental Results

• Result 1: The majority of alpha particles passed through the foil undeflected.
• Result 2: Some of these particles suffered deviation.
• Result 3: Very few rebounded and turned back.

Interpretation and Consequences

The interpretation was that particles that crossed the foil showed that atoms are not solid, but contain much empty space.

The Consequences of the Rutherford Atomic Model... Continue reading "Atomic Structure Fundamentals: Models, Particles, and Radioactivity" »