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

Core Concepts in Organic Chemistry

Nucleophilic Substitution Reactions

SN1 Reaction: Unimolecular Substitution

SN1 stands for Substitution Nucleophilic Unimolecular reaction. It proceeds in two steps:

1. Slow Step: Dissociation of the substrate to form a carbocation intermediate.
2. Fast Step: The carbocation combines with the attacking nucleophile.

Characteristics of SN1 reactions:

• More stable carbocation leads to a faster reaction.
• Favored by polar solvents.
• Mostly given by tertiary alkyl halides.
• Occurs with racemization.
• Follows 1st-order kinetics: Rate = k[R-X].

SN2 Reaction: Bimolecular Substitution

SN2 stands for Substitution Nucleophilic Bimolecular reaction. It proceeds in a single step, which is the rate-determining step.

Characteristics of SN2 reactions:... Continue reading "Essential Concepts in Organic Chemistry: Reactions and Mechanisms" »

Chromium: A Versatile and Essential Element

Chromium is a useful, very hard, crystalline, steel-gray metal, discovered by Louis Vauquelin in 1797 while working with a material known as Siberian red lead (crocoite). While you might think of highly polished chrome electroplating, purified chromium metal is grayish in color, but still very bright and lustrous. The attribute that makes electroplating perfect is that it's really corrosion resistant. It won't easily rust.

Chromium's symbol is: Cr. Its atomic number is 24. It is located in group 6, and period 4.

The name of the element is derived from the Greek word, chrōma, meaning color, because many chromium compounds are intensely colored.

Applications of Chromium

Chromium plating can be used to give... Continue reading "Chromium: Properties, Uses, and Benefits of Element 24" »

Understanding Substance Separation Methods

Separating mixtures is a fundamental process in chemistry and daily life. These techniques leverage differences in physical or chemical properties of the components. Below are common methods for separating substances, categorized by the primary property exploited.

Separation Based on Physical Properties

Magnetization

• Principle: Magnetic properties.
• Process: Magnetic materials are attracted to a magnet, separating them from non-magnetic substances.
• Example: Separating iron filings from sand.

Sieving

• Principle: Particle size.
• Process: Larger solid substances are retained by the sieve, while smaller ones pass through.
• Example: Separating stones from sand.

Filtration

• Principle: Particle size.
• Process: A solid substance

Fundamental Chemistry Definitions

Chemical Bond

The force that holds two or more atoms together to form a compound.

Litmus Paper

Paper strips containing litmus, available in both blue and red, used to indicate pH.

Ionic Compound

A compound formed from oppositely charged ions.

Hydronium Ions

Ions (H₃O⁺) that form when a hydrogen ion (H⁺) separates from an acid and bonds with a water molecule (H₂O).

Hydroxide Ion

Ions (OH⁻) that form when a base dissolves in water and dissociates.

Brittleness

The tendency of ionic compounds to be brittle solids at room temperature, causing them to break apart easily when struck.

Corrosive

A property of a substance that causes destruction or damage upon contact with other materials.

Melting Point

The temperature at... Continue reading "Understanding Core Chemistry Terms" »

Essential Scientific Vocabulary

• Nitrogen Fixation: Any process that causes nitrogen to combine with other elements to form compounds such as ammonia, nitrates, and nitrites.
• Neutralization: The process of adding an acid and a base together to achieve a neutral pH.
• Macronutrients: Nutrients that we need in larger quantities to provide us with energy.
• Micronutrients: Vitamins and minerals needed by the body. A deficiency or surplus of them can cause severe health issues.
• Carbohydrates: Sugar molecules. Along with proteins and fats, carbohydrates are one of three main nutrients found in foods and drinks.
• Lipid: Organic fats that are insoluble in water.
• Osmosis: The movement of molecules through a selectively permeable membrane.
• Hydrolysis: A chemical

• Isotopes

  • Same elements with different numbers of neutrons

• Ions

  • Same element with an unequal number of protons and electrons

• Electric Fields

  Things with charge (protons and electrons) generate electric fields (E) (Likewise, electric fields can affect things with charge)

• Energy and Matter

  When atoms or molecules “happen across” energy, [usually] 1 of 2 things can happen: 1) they wiggle-jiggle more [we classify the amount of “wiggling-jiggling” by the quantity of temperature] 2) the energy, if it is a) in the form of a special type of electromagnetic field and b) of a specific frequency, can be absorbed

  λ∙f = c

  λ = wavelength of the wave [m]

  f = frequency of the wave [Hertz, Hz=1/s]

  c = speed of light = 3∙108 m/s

  Electromagnetic Waves

Dalton's Atomic Theory

John Dalton proposed that elements were made up of little solid spheres without internal structure. Atoms of the same element were equal. Atoms combine, forming compounds. Depending on the ratio, we can have different compounds.

J.J. Thomson

First model of the atom (1904). He discovered/proved the existence of tiny, negatively charged particles: electrons.

Rutherford's Model of the Atom

Gold foil experiment, Ernest Rutherford (1911). Alpha particles are tiny, positively charged particles much smaller than an atom. An atom is mostly empty space. Some particles will bounce back, and some others will pass but in a different way. The nucleus is something dense and positively charged.

Thomson's Atomic Model

In 1904, Thomson's atomic... Continue reading "Dalton's Atomic Theory and the Evolution of Atomic Models" »

Chemical Reactions

occurring at low temperatures are
                _______low______ than reaction rates of chemical reactions occurring at high
temperatures.

40. Increasing pressure causes gas particles to             ______collide_______________. This
                ________increases______________ the reaction rate of a chemical reaction.

41. All reactions require    ___activation energy___________ for chemical bonds to begin breaking.

Exercise 3 – Analyzing the Financial Impact of Price and Volume Changes on Apple iPhones

Apple iPhone Sales and Manufacturing Costs

In 2014, Apple sold approximately 150,000,000 iPhones at a price of $640 per unit. The company's average manufacturing cost per iPhone is detailed in Table 1.

Table 2 outlines Apple's fixed costs associated with its iPhone business.

1. Gold Extraction

   Gold is found mainly as the metal itself in the earth because it has a low reaction rate, which prevents easy oxidation.

Carbon Extraction of Zinc

Carbon can be used to extract zinc because carbon has a higher reaction rate than zinc.

Sodium Extraction

Sodium was not extracted until 1807 because sodium attaches itself very strongly to other elements, making it difficult to separate and obtain a pure substance.

Limestone

i) Name of Material: Limestone

Reason why this metal is used: It decomposes silicon dioxide in the heat of the furnace to calcium oxide.

ii) Word Chemical Equation for the Reaction of Iron Extracted from Iron Ore when a Gaseous Oxide of Carbon Reacts with Iron Oxide: FeO + CO = Fe + CO2

Aluminium Extraction

i) Why a Mixture... Continue reading "Extraction of Metals and Chemical Reactions" »