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

Chapter 11: Modern Atomic Theory

Evolution of Atomic Models

Rutherford's Model: This model contains a dense nucleus with electrons outside and consists of mostly empty space. However, it could not explain electron arrangement or why electrons do not collapse into the nucleus.

Bohr Model: Bohr incorrectly assumed that electrons travel around the nucleus in fixed orbits.

Wave Mechanical Model: This is the modern model where electrons have both particle and wave properties instead of fixed orbits; it utilizes orbitals.

Electromagnetic Radiation and Energy

Electromagnetic Radiation is energy transmitted through space and light. Wavelength (λ) is the distance between wave peaks, while Frequency (ν) is the number of waves passing a point per unit of... Continue reading "Modern Atomic Theory and Molecular Geometry" »

Multiple Choice Answer Key

• 1) Answer: B. H₃PO₄ + 3NaOH → Na₃PO₄ + 3H₂O
• 2) Answer: B. NH₄⁺(aq) + H₂O(l) ⇌ H₃O⁺(aq) + NH₃(aq)
• 3) Answer: B. Basic since K_a < K_b
• 4) Answer: C. 3.33 M
• 5) Answer: D. K_b = [H₂CO₃][OH⁻] / [HCO₃⁻]

Additional Answers: 6. B, 7. A, 8. B, 9. B, 10. B, 11. A, 12. C, 13. D, 14. D, 15. B, 16. B, 17. A

Detailed Solutions for Chemistry Problems

Question 1: Titration of Oxalic Acid

Part A: Determining NaOH Molarity

Trial 1 Volume: 24.00 mL − 5.85 mL = 18.15 mL (Outlier)
Trial 2 Volume: 40.05 mL − 24.00 mL = 16.05 mL
Trial 3 Volume: 21.45 mL − 5.50 mL = 15.95 mL

Average Volume: (16.05 mL + 15.95 mL) / 2 = 16.00 mL = 0.01600 L

Chemical Equation: H₂C₂O₄ + 2NaOH → Na₂C₂O₄ + 2H₂O

• Moles H₂C₂O₄: (0.175 M)(0.01600

Heat-Treatable Wrought Aluminum Alloys

Heat-treatable wrought aluminum alloys possess medium-high mechanical strength, which is significantly higher than that of non-heat-treatable alloys.

2xxx Series: High-Strength Al-Cu Alloys

The 2xxx series (Al-Cu) utilizes copper as the primary alloying element, often with additions of Mg, Mn, Si, and Ni (as well as Ti, Cr, or Zr). Ternary Al-Cu-Mg alloys, known as "duralumin," exhibit high solubility at high temperatures.

• High-Temperature Aging: This process results in superior mechanical properties, with the maximum temperature limited by the solidus temperature (T-solidus).
• Overheating: Excessive heat leads to low Ultimate Tensile Strength (UTS) and reduced ductility due to intergranular cracks and high

Alcohols, Thiols, Ethers, Aldehydes, and Ketones

1. Identifying Functional Groups

• Alcohol: -OH group attached to a carbon atom.
• Phenol: -OH group attached directly to a benzene ring.
• Thiol: -SH group (sulfhydryl group).
• Ether: C-O-C linkage (oxygen atom bonded to two carbon groups).
• Aldehyde: -CHO group (carbonyl group at the end of a chain).
• Ketone: C=O group (carbonyl group) located in the middle of a chain.

2. Naming Conventions (Nomenclature)

• Alcohol: Replace the alkane suffix “-e” with “-ol” (e.g., ethanol).
• Phenol: Named as phenol, often requiring position numbers.
• Thiol: Use the suffix “-thiol”.
• Ether: Name both alkyl or aryl groups, followed by the word “ether”.
• Aldehyde: Use the suffix “-al”.
• Ketone: Use the suffix “-one”.

Chemical Equilibrium & Enthalpy Changes

Le Chatelier's Principle & Equilibrium Constant (Kc)

• If a reaction is endothermic, an increase in temperature will shift the equilibrium to the right-hand side (products) to decrease the temperature.
• Position of Equilibrium: Describes how far a reaction has proceeded and the proportion of products to reactants in the mixture.
• Equilibrium Constant (Kc): The constant for an equilibrium system, expressed in terms of concentrations (mol dm^-3) at a given temperature.
• Kc Formula: Kc = [Products] / [Reactants]
  • Example (Haber Process): N₂(g) + 3H₂(g) ⇌ 2NH₃(g)
  • Units for Haber Process Kc: (mol dm^-3)^-2 or mol^-2 dm⁶
• Temperature Effects on Kc/Kp:
  • For an exothermic reaction, an increase in temperature decreases Kc/

Extraction of Zinc (Zn)

Major Ores of Zinc

• Zinc blende (ZnS)
• Calamine (ZnCO₃)
• Zincite (ZnO)

Zinc is primarily extracted from calamine and zinc blende ores.

Extraction from Calamine Ore

Zinc oxide is obtained by calcining calamine:

ZnCO₃ → ZnO + CO₂↑

Zinc metal is then obtained by heating zinc oxide (ZnO) with coal powder:

ZnO + C → Zn + CO↑

Extraction from Zinc Blende

Zinc oxide (ZnO) is obtained by roasting concentrated zinc blende at high temperatures in the presence of air:

2ZnS + 3O₂ → 2ZnO + 2SO₂↑

The resulting ZnO is reduced using the carbon method described above.

Purification of Zinc

The zinc obtained is impure and is purified via electrolysis. A pure aluminum sheet serves as the cathode, while impure zinc acts as the anode in... Continue reading "Industrial Extraction Processes for Zinc and Aluminum" »

Phase Change Materials (PCM)

PCMs are substances that absorb or release heat during phase transitions, typically triggered by temperature changes. They store energy as latent heat.

Types of PCMs

• Organics (Paraffins, Fatty Acids): Characterized by high latent heat, chemical stability, and non-corrosive properties. They do not suffer from supercooling but exhibit low thermal conductivity and are flammable.
• Inorganics (Salts and Hydrates): Offer high thermal storage density and conductivity at a low cost. However, they are corrosive, chemically unstable, and often require subcooling to solidify.

Technical Note: PCMs absorb heat when melting and release it during solidification, effectively maintaining internal temperatures.

Corrosion Mechanisms and

Method 1: The Chemical Path

Δ_rH_m = Molar Enthalpy (kJ/mol)

Trigger: Only when a chemical reaction has taken place.

• ΔH_rxn = Enthalpy change of the whole reaction
• Δ_rH_m = Q_rxn / n
• Q_rxn = Heat of Reaction (kJ)

H₂O data: Mass or volume of water given. Chemical data: Mass, concentration, or moles of reactant burnt or dissolved.

Q_rxn = -Q_water

Note: If chemicals and water are involved in the reaction, flip the signs for Q_rxn and Q_water; if it is just warming, do not flip the signs.

Method 2: The Physical Phase Change Path

No chemical reaction; only temperature change or physical change occurs.

Scenario A: Changing Temperature (Substance stays same)

Q = mcΔT

• Units: Q (J or kJ) | m (g) | c (J/g·°C) | ΔT (°C)

Scenario B: Constant Temperature (Melting, boiling,

pure substance: is a phase of uniform composition and unchanging can not be decomposed into other substances of different classes by physical methods.

elements: they are pure substances that can not be decomposed into simpler ones through normal chemical processes.

compounds: they are pure substances made up of two or more elements, which can be decomposed by chemical methods on the elements of which are constituted. A compound always has the same elements and the same proportions regardless of the process followed.

Blended is an aggregation of different substances without causing any chemical reaction between them and therefore may be separated by physical methods.

ponderal laws: they refer to the quantity of matter of different substances... Continue reading "Laws ponderal" »

Organic Synthesis and Reaction Mechanisms

Malonic Ester Synthesis and Carbonyl Reactivity

Electrophiles (e+) for Malonic Ester Synthesis include epoxides, primary haloalkanes, and conjugated ketones. Esters react with 2 equivalents of irreversible nucleophiles, such as LiAlH4 and RMgBr, to yield an alcohol product. Acyl halides undergo fast hydrolysis and do not require a catalyst because the acyl halide is a better electrophile compared to carboxylic acids, and Cl- is a better leaving group than OH-.

Carbohydrate Chemistry

• Reducing sugars contain hemiacetals at the anomeric carbon.
• Alpha 1,4-linked polyglucans are known as amylose, used for energy storage in plants (digestible by humans).
• Oligosaccharides consist of 3-10 units.
• Reduction of monosaccharides