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

Mixing and Measuring

Agitator

An agitator is a machine used for mixing liquids, typically with an electromagnet.

Beaker

A beaker is a cylindrical container made of glass that is very commonly used in the laboratory, mainly to prepare or heat substances.

Burette

A burette is used for decantation and for transferring and dispensing liquids or fluids.

Graduated Cylinder

A graduated cylinder is used to measure volumes of liquids.

Micropipettes

Micropipettes are used to measure and extract very small amounts of liquids from a solution.

Pipette

A pipette is used to accurately measure volumes of liquids.

Volumetric Flask

A volumetric flask is used to prepare solutions and to know the volume.

Heating and Support

Bunsen Burner

A Bunsen burner is used to heat chemical... Continue reading "Essential Lab Equipment: Uses and Functions" »

Chemistry Fundamentals

Physical Changes

Affect only physical properties like physical state. They do not alter the nature of the substance. Example: Frozen and liquid water have the same composition; nothing changes chemically.

Chemical Changes

Occur when there is a change in the composition of matter. Example: Paper converting into a gas (combustion).

Indicators of Chemical Change

• A gas is produced (bubbles are formed).
• There is a change in temperature due to heat exchange between the environment and reacting substances.
• A precipitate is formed (an insoluble solid that appears as a result of the reaction between solutions).
• The color changes.

Related Concepts

Heat: The interchange of thermal energy between objects or substances having different temperatures.... Continue reading "Fundamental Concepts in Chemistry" »

Distillation: Separating Liquids by Boiling Point

Distillation is a separation process for components of a mixture that have different boiling points. The mixture is heated until it reaches the lower boiling point. One of the substances then becomes vapor and can be separated. This vapor is cooled until it condenses and is collected in a vessel.

Crystallization: Forming Pure Solid Crystals

Crystallization is the process of forming solid crystals from a liquid solution, typically by evaporating the solvent. When all the liquid has evaporated, the solid crystals remain at the bottom of the vessel.

Paper Chromatography: Separating Organic Substances

Paper chromatography is used to separate several organic substances that travel through the chromatography... Continue reading "Chemical Separation Techniques and Mixture Classification" »

How to Change a Typewriter Ribbon

To verify if the ribbon is completely spent, set the ribbon color selector to the other color and type several words. Often, on a two-color ribbon, only the top half is used up while the other half remains new.

1. Carefully observe how the ribbon is threaded through the machine's guides. Note particularly if the spool is wound from the outside in.
2. Set the ribbon color selector to red and press two keys simultaneously until they lock in the up position. This will hold the ribbon carrier up and make it easier to change.
3. Wind the entire used ribbon onto one of the spools.
4. Unthread the ribbon from the guides and remove both spools from the machine. Detach the old ribbon from the now-empty spool.
5. Unroll approximately 12

Paradigmatic (vertical) axis

The words organizations, groups, and Amnesty International are related to each other because they all belong to the same semantic group, a relationship known as hyponymy. Organizations serve as a hypernym (a more general or superordinate word), while human rights groups and Amnesty International serve as hyponyms (more specific words, in this case types of organizations). The other two kinds of paradigmatic relationships are those of synonymy (prompted = caused) and antonymy (weak/strong).

Syntagmatic (horizontal) axis
 Unlike the paradigmatic relationships, the syntagmatic relationships of a word are not about meaning. They are about the lexical company the word keeps (collocation) and the grammatical patterns

Fundamentals of Materials and Chemistry

Construction Materials and Compounds

Materials include pre-fabricated and worked products such as ADVEST, TRUPAN, MASISA, Cholguán, CEMENT, and Vulcanite.

Key Compounds

• Tannin: Provides a coffee wood color.
• Mortar/Concrete: A mixture typically composed of sand, cement, and stone.

Atomic Structure and Elements

A compound is formed from atomic elements. Key concepts include:

• Atomic Number (No.): The number of electrons (or protons).
• Atomic Mass (A): Represents the energy contained within the protons and electrons.
• Symbol: The abbreviation for the element. (Note: Atomic mass is often referred to as atomic weight.)

Key Elements Data

The following table lists elements by Symbol, Atomic Number (No.), and Atomic Mass (... Continue reading "Chemical Principles, Gas Dynamics, and Construction Materials" »

Functions and Activity of Water (H2O)

Water acts as a stabilizer of body temperature, transports nutrients and degradation products, and serves as a reagent in chemical reactions. It also acts as a stabilizer, forming polymers.

Connected Water Molecules

Water in contact with solutes and other aqueous constituents exhibits reduced mobility. This water freezes at approximately -40 ºC. The degree of H2O connection includes constitutional water, vicinal water, and multilayer water. This connected water is available for the growth of microorganisms and for enzymatic reactions.

Types of Bound Water in Food

• Constitutional Water: Represents a small fraction of the H2O present in food with high moisture content. It is water strongly linked to the aqueous

Its function is to complete the measurement circuit, providing a passage from the conductivity-sensing electrode, through the solution, to the reading device. The four parts form an electrical circuit.

Types of Electrodes

1. Hydrogen Electrode
2. Calomel Electrode: Consists of a mixture of mercury and mercurous chloride in contact with a potassium chloride solution.
3. Silver Chloride Electrode
4. Glass Electrode:
   • Parts: Lead-plated, resin-filled rod, internal electrode, sensitive glass.
5. Glass Electrode and Calomel: External calomel reference, two different cells connected in series.

Analysis Methodology

To analyze a substance using potentiometric techniques (anions, cations, organic and inorganic), the substance, or some of its possible complexes, must be electroactive... Continue reading "Potentiometric Analysis: Electrodes, Methods, and Factors" »

Understanding Chemical Bonds

Ionic Bond: This bond occurs when metallic elements interact with non-metal atoms. In this case, the metal atoms donate electrons to the non-metal atoms, becoming positively and negatively charged ions, respectively. These oppositely charged ions are attracted by strong electrical forces, being tightly bound and giving rise to an ionic compound. These electrical forces are called ionic bonds.

Covalent Bond: Covalent bonds are the forces that hold non-metallic atoms together. These atoms have many electrons in their outermost level (valence electrons) and tend to gain electrons rather than transfer them to acquire the stability of the electronic structure of a noble gas. Therefore, electrons from non-metallic atoms... Continue reading "Understanding Chemical Bonds: Ionic, Covalent, and Metallic" »