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

Cell Observation Techniques

Aim: Observe Cells and Subcellular Structures

• Add specimen (e.g., onion epidermis) on a slide.
• Stain (e.g., iodine) to highlight structures.
• Lower cover slip at an angle to reduce air bubbles.
• Use low → high magnification.
• Focus using coarse → fine adjustment.
• Label parts of the microscope.
• Calculate magnification.
• Measure size using a scale bar.
• Understand differences between plant and animal cells.
• Explain why staining is used (to see organelles like the nucleus).

Investigating Osmosis

Aim: Investigate Osmosis with Potato Cylinders

• Cut identical potato pieces.
• Weigh each piece, then place in sugar solutions of different concentrations.
• Leave for 24 hours, then dry and reweigh.

Experimental Variables:

• Independent Variable (IV)

How is a pure semiconductor changed into an N-type material?

An N-type semiconductor is created when pure semiconductors, like Si and Ge, are doped with pentavalent elements. When a pentavalent atom replaces a Si atom, four of its electrons bond with four neighboring Si atoms, leaving one free electron.

What is the difference between P and N type materials?

N-type semiconductors have an excess of electrons, while P-type semiconductors have an excess of "holes" where an electron could exist.

What are the uses of diodes?

The most basic function of a diode is changing AC current to DC current by removing some part of the signal. This makes them rectifiers. They are also used in electrical switches and surge protectors because they can prevent voltage... Continue reading "Key Concepts in Electronics, Energy, and Basic Science" »

Physical Adsorption (Physisorption)

• It occurs due to weak van der Waals forces between the adsorbent and adsorbate.
• The enthalpy of adsorption is low, typically between 20–40 kJ/mol.
• It is usually non-specific and can occur on many types of surfaces.
• It is reversible in nature and can be undone by changing pressure or temperature.
• Physisorption is favored at low temperatures.
• It can result in the formation of multiple layers of adsorbed molecules.
• Little to no activation energy is required for physisorption.

Chemical Adsorption (Chemisorption)

• It involves the formation of strong chemical bonds (covalent or ionic) between the adsorbent and adsorbate.
• The enthalpy of adsorption is high, ranging from 40–400 kJ/mol.
• It is highly specific and depends on

Electroanalytical Fundamentals

• Common electroanalytical methods
• Electrochemical cell fundamentals
• Potential in electrochemical cells
  • No current: Nernst Equation
  • With current: Ohmic Resistance and Polarization

What is Potentiometry?

• Potentiometry involves measuring the electrochemical potential between two electrodes in a solution. This potential difference (voltage) is related to the concentration of ions in the solution according to the Nernst Equation.

General Principles of Potentiometry

• Reference Electrode:

  • Known, fixed potential
    • Silver/Silver Chloride (Ag/AgCl)
    • Calomel

• Indicator Electrode:

  • Sensitive to concentration of analyte
    • Metallic
    • Ion-Selective
• Measure E_cell (negligible current flows through the cell)
• Correct E_ref and E_j (Junction Potential)
• Compute

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" »

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

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" »