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

Defining Creams and Pastes

Creams

Creams are semi-solid emulsions used externally on the skin. They can be either oil-in-water (O/W) or water-in-oil (W/O) emulsions. They are used for moisturizing, healing, or delivering drugs through the skin.

• Example: Cold Cream (W/O), Vanishing Cream (O/W)

Pastes

Pastes are also semi-solid but contain a high amount of insoluble powders (around 25-50%), making them stiffer and more absorptive. They form a protective layer on the skin and are used where longer contact is needed.

• Example: Zinc Oxide Paste

Understanding Pharmaceutical Aerosols

Aerosols are pressurized dosage forms that release active ingredients as a fine spray, mist, or foam when a valve is opened. They use propellants (like hydrocarbons or compressed... Continue reading "Pharmaceutical Dosage Forms: Creams, Powders, and Solutions" »

Essential Chemistry Definitions

Fundamental Concepts

• Physical Property: Characteristics observed without changing the substance (color, melting point, density, boiling point).
• Chemical Property: Characteristics observed when a substance changes into another (reactivity with air, acid, base, water, other chemicals).
• Law of Conservation of Matter: Matter is neither created nor destroyed.
• Atomic Theory: Theory of the nature of atoms.
• Isotope: Atoms of the same element with different numbers of neutrons.
• Ion: Atom or molecule with a net electric charge.
• Cation: Positively charged ion.
• Anion: Negatively charged ion.
• Atomic Mass Unit (amu): Unit of mass for expressing atomic & molecular weights.
• Mole: Unit for amount of substance (6.022 x 10^23 particles)

The Law of Conservation of Mass

Matter cannot be created or destroyed. The number of atoms in the reactants must be the same as the products. Atoms don't appear or disappear, they just rearrange. (Hence why you have to balance out chemical equations)

Balancing Equations

• The subscripts in the chemical formula cannot be changed (The little number beside a formula that is part of it).
• Use coefficients to balance.
• Coefficients multiply the entire compound by that number (4PO = 4P 4O).

Example: N₂+O₂>N₂O = 2N₂+O₂>2N₂O

Balancing Word Equations

• Determine what the reactants and the products are, convert names to chemical formulas. (Individual elements that are diatomic (molecular) will be, S₈, P₄, I₂, Br₂, Cl₂, F₂, O₂, N₂, H₂) If it's not diatomic just

Classifying Matter

• Pure Substance: Element or compound.
• Mixture: Homogeneous (uniform) or heterogeneous (non-uniform).
• Element: One type of atom.
• Compound: Two or more atoms chemically bonded.

Properties of Matter

• Physical: Observable without changing the substance (e.g., color, density).
• Chemical: Describes the potential for a substance to change (e.g., reactivity).
• Physical Change: No new substance is formed (e.g., melting).
• Chemical Change: A new substance is formed (e.g., burning).

Atomic Structure

Protons, Neutrons, Electrons (PEN)

• Protons: Positive charge (+1), located in the nucleus.
• Neutrons: No charge (0), located in the nucleus.
• Electrons: Negative charge (-1), located in shells around the nucleus.
• PEN Relationships:
  • Protons = Atomic number.
  • Neutrons

Spaghetti Carbonara

Utensils and Ingredients

Utensils

• Large pot
• Large skillet
• Colander
• Large bowl
• Whisk or fork
• Tongs or a pasta fork
• Spoon or ladle

Ingredients:

• 400g spaghetti
• 200g pancetta or bacon, diced
• 4 large eggs
• 1 cup grated Parmesan cheese
• 4 cloves garlic, minced
• Salt and black pepper to taste
• 2 tablespoons olive oil
• Chopped parsley for garnish (optional)

Instructions

1.

Boil the Spaghetti

Start by boiling a large pot of salted water. While waiting, dice the pancetta, mince the garlic, and grate the Parmesan cheese.

2.

Cook the Spaghetti

Once the water boils, add the spaghetti and cook until al dente. Once cooked, reserve about a cup of pasta water before draining.

3.

Sauté the Pancetta and Garlic

In a large skillet, heat the olive oil over medium heat. Add... Continue reading "Classic Spaghetti Carbonara Recipe" »

Principle of Chromatography - Chromatography is a separation method where the analyte is combined within a liquid or gaseous mobile phase, which is pumped through a stationary phase. Usually, one phase is hydrophilic and one is lipophilic. The components of the analyte interact differently with these two phases. Depending on their polarity, they spend more or less time interacting with the stationary phase. This leads to the separation of different components present in the sample. Each sample component elutes from the stationary phase at a specific time called retention time.

Types of Chromatography

1. Liquid Chromatography - This type of chromatography is used to separate and analyze non-volatile compounds. In this technique, the sample is dissolved

Chemical Reactions and Equations

1. Chemical Reaction Definition

The process in which a substance undergoes change to produce new substances with new properties is known as chemical reaction, e.g., magnesium carbonate when heated produces magnesium oxide and carbon dioxide (i.e., new substances with new properties).

A chemical change is generally accompanied by a change of state, change of colour, evolution of a gas, or change of temperature, etc.

2. Chemical Equation Definition

The qualitative representation of a chemical reaction in a shorthand or concise form, in terms of symbols and formulae, is called a chemical equation.

3. Skeletal Chemical Equation

A chemical equation written in the form of symbols and formulae is called a skeletal chemical

Chemical Bonding Fundamentals

Definition and Purpose

Definition: Attractive forces holding atoms together in compounds.

Purpose: Atoms bond to achieve stability, often attaining a noble gas electron configuration.

Lewis Structures and the Octet Rule

Lewis Symbols

Dots represent valence electrons around elemental symbols.

The Octet Rule

Atoms tend to have eight electrons in their valence shell.

Limitations of the Octet Rule

It doesn't apply to all elements; some have incomplete or expanded octets.

Types of Chemical Bonds

• Ionic Bond: Electron transfer between atoms, forming charged ions.
• Covalent Bond: Sharing of electron pairs between atoms.
• Coordinate (Dative) Bond: Both shared electrons come from the same atom.

Bond Parameters

• Bond Length: Distance between

Chapter 12: Chemical Kinetics

1. Reaction Rate & Stoichiometry

For aA+bB→cC+dD:

Rate = −(1/a)∗Δ[A]/Δt = −(1/b)∗Δ[B]/Δt = (1/c)∗Δ[C]/Δt = (1/d)∗Δ[D]/Δt

• Rate is always positive. Reactants are negative, products positive.
• Ex: 2NO2​→2O2​. If Rate of disappearance of NO2​=0.010: Rate = −(1/2)∗(0.005 M/s. Rate of formation of O2​=0.005. Rate of formation of NO=20.005 M/s=0.010.

2. Rate Laws & Reaction Order

Rate = k[A]m[B]n

• k: Rate constant (temp-dependent)
• m,n: Reaction orders (exp. Determined)
• Overall Order = m+n
• Method of Initial Rates: Compare two experiments where only one reactant's conc. Changes. (Rate/Rate) = ([A]2​/[A]1​)
  • If Rate x2 when [A] x2 ⟹m=1 (1st order)
  • If Rate x4 when [A] x2 ⟹m=2 (2nd order)

Structure of the Atom

Protons, Electrons, and Neutrons

Protons: Equal to the atomic number

Electrons: Equal to the atomic number

Neutrons: Equal to the atomic mass minus the atomic number

Bohr-Rutherford Diagram

Electron shells: 2, 8, 8, 18, 18, 32

Counting Atoms

Example 1: Na₂CO₃

• Sodium (Na): 2
• Carbon (C): 1
• Oxygen (O): 3

Example 2: 4Al₂(CO₃)₃

• Aluminum (Al): 4 x 2 = 8
• Carbon (C): 3 x 4 = 12
• Oxygen (O): 9 x 4 = 36
• Total: 56

Ions and Ionic Compounds

Ions are atoms that have either lost or gained electrons. While atoms are neutral, ions are charged particles.

Ionic Compounds are a combination of a cation (positive ion) and an anion (negative ion), typically formed between a metal and a nonmetal.

Example: Calcium Chloride (CaCl₂)

Calcium (Ca⁺²) has a charge of +2,... Continue reading "Structure of the Atom, Chemical Reactions, and Acids and Bases" »