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

Kinetic Theory of Matter

• Matter is made up of particles.
• These particles are constantly moving because they have kinetic energy.
• There are spaces between the particles.
• There are attractive forces between particles, and these become stronger as the particles move closer.
• All particles have energy. The temperature of a substance is a measure of the average kinetic energy of the particles.
• A change in phase may occur when the energy of the particles is changed.

Boyle's Law

The pressure of a fixed quantity of gas is inversely proportional to the volume it occupies, as long as the temperature remains constant. P₁ × V₁ = P₂ × V₂

Gay-Lussac's and Charles's Law

The volume of an enclosed sample of gas is directly proportional to its absolute temperature, provided... Continue reading "Matter: Kinetic Theory, Properties, and Classifications" »

Scientific models used to explain why and how atoms form molecules:

• Lewis dot structure
• Valence bond theory

Valence bond theory describes a covalent bond as the overlap of half-filled atomic orbitals (each containing a single electron) that yield a pair of electrons shared between the two bonded atoms. According to valence bond theory, a covalent bond results when two conditions are met: (1) an orbital on one atom overlaps an orbital on a second atom and (2) the single electrons in each orbital combine to form an electron pair.

• Molecular orbital theory

model that describes the behavior of electrons delocalized throughout a molecule in terms of the combination of atomic wave functions. It describes the distribution of electrons in molecules in much... Continue reading "Atomic Models, Periodic Trends, and Chemical Bonding" »

IONIC: thet are solids at room temperatures and have medium to high meltin and boiling points. Ionic bond is strong because it is electrostatic. They are very hard. It is not eassy to scratch an ionic compound. They are fragile. Hitting them forces ions with the same signs together, and they repel and break the crystal. Most disolve well in water, water molecules may surround the ions,weakening their bonds and separating them from the crystal lattice. This is called solvation. They do not conduct electricity well in solid state but hey do in solution or liquid state. SODIUM CHLORIDE

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" »

Colloids and Solutions

Colloids resist filtering, although some particles are retained in the filter. These particles can be detected by the scattering of light when it passes through the mixture; this property is called the Tyndall effect. Common examples of colloids include milk and certain juices.

In contrast, actual solutions contain particles with sizes similar to atoms or molecules (less than 1 nm). These cannot be filtered or decanted and do not exhibit the Tyndall effect.

Concentration and Solubility

The composition of a solution refers to the relative amount of solute in the mixture. Solutions have variable compositions, and their properties depend directly on these proportions. To describe a solution accurately, one must identify its... Continue reading "Understanding Colloids, Solutions, and Solubility" »

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

Heterogeneous Separation Techniques

Decantation Using a Separating Funnel

Two immiscible liquids which have different densities can be separated by decanting using a separating funnel. The process follows these steps:

• First, pour the mixture into the separating funnel.
• Wait several minutes until a clear separation boundary is formed.
• Finally, drain the heavier phase into a beaker or Erlenmeyer flask.

Decanting is an alternative separation technique for an insoluble solid and liquid mixture, but it is generally less suitable than filtering.

Liquid Extraction

This method is used for separating a substance which has different solubility in two immiscible liquids, usually water and an organic solvent. When both solvents are mixed, the substance transfers... Continue reading "Separation Methods for Chemical Mixtures" »