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AECHE Task 4 Cheatsheet

08/03/2026

AECHE Task 4 Cheatsheet

  1. Nanomaterials & Separation Techniques 1.1 Nanomaterials & The Nanoscale
  • Nanoscale: Refers to any structure that is between 1 and 100 nanometres across. A nanometre (nm) is one-billionth of a metre (10^-9 m).
  • Nanomaterials: Natural or synthetic substances composed of single units that exist on the nanoscale. Materials larger than this are called bulk materials.
  • Surface Area to Volume Ratio: Nanoparticles have a massively increased surface area to volume ratio compared to bulk materials. This makes surface area effects (quantum effects) more pronounced, dramatically altering the properties of the material (e.g., optical properties, conductivity, heat sensitivity).
  • Fabrication Techniques:
    • Top-down fabrication: Starts with a bulk material and progressively removes or grinds it down until the required nanoscale size/shape is achieved. It is cheap and produces uniform products, but is limited to simple structures.
    • Bottom-up fabrication: Involves physically building or growing the required material atom by atom or molecule by molecule. Allows for highly complex structures but is currently uneconomical for commercial scale-up.
  • Health & Environmental Concerns: Due to their small size, nanoparticles can easily travel through the air, skin, bloodstream, and into cells. This can cause respiratory issues or unwanted chemical reactions inside the body. Long-term effects remain largely unknown. 1.2 Separation Techniques Separation techniques rely on differences in physical and chemical properties. Note: You only need to know the property used for separation, not the intricate processes.
  • Separation by Particle Size:
    • Sieving: Uses a mesh to let smaller particles pass while trapping larger ones.
    • Filtration (Gravitational & Vacuum): Separates solid particles from liquids or gases. The liquid passing through is the filtrate; the solid left behind is the residue.
  • Separation by Density: (Denser substances sink; less dense float).
    • Sedimentation & Decantation: Heavy solids settle to the bottom (sedimentation), and the liquid is carefully poured off (decantation).
    • Separation Funnels: Used for immiscible (unmixable) liquids. The denser liquid sinks and is drained out of a tap.
    • Centrifugation: Rapid spinning forces denser particles to the outside/bottom of a container.
  • Separation by Boiling Point (Volatility):
    • Evaporation: Boils off the volatile liquid (solvent) to recover the non-volatile dissolved solid (solute).
    • Distillation: Vaporizes a liquid and cools it in a condenser to collect the purified liquid (distillate).
    • Fractional Distillation: Separates miscible liquids with slightly different boiling points (e.g., crude oil) using a fractionating column.
  • Separation by Electric Charge:
    • Electrostatic Separation: Uses electrostatic forces to attract charged particles (like smoke/pollutants) to oppositely charged plates.
  • Separation by Affinity:
    • Chromatography: Separates components based on their varying affinity (attraction) for a stationary phase versus a mobile phase.
  1. Carbon Allotropes & Lattices Allotropes are different structural arrangements of atoms of the same element, giving them different physical forms and properties. 2.1 Network Lattices (Diamond & Silica)
  • Covalent Network Lattices: Atoms are bonded in a continuous 3D structure by strong covalent bonds with no weak intermolecular forces.
    • Properties: Extremely hard and brittle, extremely high melting/sublimation points, and non-conductive (electrons are locked in fixed positions).
  • Diamond (Carbon): Each carbon atom forms 4 single covalent bonds to neighboring carbon atoms in a rigid 3D tetrahedral arrangement.
    • Properties: Hardest naturally occurring substance, sublimes at >3500 degrees C, non-conductive, used in cutting/drilling tools.
  • Silica (SiO2): A continuous network where each Silicon is bonded to 4 Oxygens, and each Oxygen is bonded to 2 Silicons. Major component of quartz, sand, and glass. 2.2 Layer Lattices (Graphite)
  • Graphite (Carbon): A covalent layer lattice. Each carbon is covalently bonded to 3 others in flat, 2D hexagonal rings, leaving one delocalized valence electron per carbon atom.
  • Structure: Consists of multiple layers (graphene sheets) stacked together. Strong covalent bonds exist within the layers, but only weak dispersion (van der Waals) forces exist between the layers.
  • Properties:
    • Conductive: Free delocalized electrons can move and conduct electricity.
    • Soft & Slippery: Weak forces between layers allow them to slide over each other easily.
    • High Heat Resistance: Strong covalent bonds within layers prevent melting at low temperatures. 2.3 Carbon Nanomaterials (Fullerenes)
  • Fullerenes: A family of carbon allotropes engineered on the nanoscale, characterized by atoms arranged in pentagons and hexagons.
  • Buckyballs (e.g., C60): Spherical molecules. Soft, slippery, low melting points, and insoluble in water. Used in biomedicine and targeted drug delivery.
  • Graphene: A single, isolated layer of graphite. Retains electrical conductivity but is extremely strong and tough.
  • Carbon Nanotubes: Hollow cylinders with walls made of graphene. They have unique strength (300x stronger than steel), and incredible electrical and thermal conductivity.
  1. Organic Chemistry: Alkanes, Alkenes & Aromatics Hydrocarbons are compounds containing only carbon and hydrogen atoms. Crude oil is the primary source of hydrocarbons. 3.1 The Basics: Counting Carbons (Stem Names) Before you can name a molecule, you need to know the prefix that tells you how many carbons are in the longest chain:
  • 1 C = Meth-
  • 2 C = Eth-
  • 3 C = Prop-
  • 4 C = But-
  • 5 C = Pent-
  • 6 C = Hex-
  • 7 C = Hept-
  • 8 C = Oct-
  • 9 C = Non-
  • 10 C = Dec- 3.2 Branches (Alkyl Groups) When a carbon chain branches off the main parent chain, it gets a “-yl” suffix.
  • -CH3 branch = Methyl
  • -CH2CH3 branch = Ethyl
  • -CH2CH2CH3 branch = Propyl 3.3 Alkanes (Saturated Hydrocarbons)
  • Definition: Alkanes contain only single carbon-carbon (C-C) bonds. Saturated means every carbon holds the maximum possible hydrogens. End in “-ane”.
  • General Formula: CnH2n+2
  • Homologous Series: A family of molecules differing by exactly one -CH2- unit. Physical properties show patterns (e.g., longer chain = higher boiling point due to stronger dispersion forces).
  • Reactivity: Generally unreactive; primarily undergo substitution and combustion. 3.4 Alkenes (Unsaturated Hydrocarbons)
  • Definition: Contain at least one double carbon-carbon (C=C) bond. Unsaturated because they don’t hold the maximum hydrogens. End in “-ene”.
  • General Formula: CnH2n (for molecules with exactly one double bond).
  • Reactivity: The double bond makes them far more reactive than alkanes; they readily undergo addition reactions. 3.5 Benzene (Aromatics)
  • Definition: A special ring of 6 carbon atoms (C6H6) with alternating double and single bonds. However, these bonds actually blur together into a “delocalized electron cloud” shared evenly around the ring.
  • Naming: It is simply called “benzene”. We do not use numbers for double bonds inside the ring (so “benz-1-ene” doesn’t exist).
  • As a branch: If a benzene ring is attached as a side-branch to a longer carbon chain, it is called a phenyl group. 3.6 IUPAC Naming Rules (Step-by-Step)
  • Find the parent chain: Identify the longest continuous carbon chain. (If it’s an alkene, this chain must include the double bond). Name it using the stems above.
  • Number the carbons: Number the chain from the end that gives the lowest numbers to the double bond (priority) or the branches.
  • Identify branches/halogens: Name alkyl groups (methyl, ethyl) or halogens (fluoro, chloro, bromo, iodo).
  • Group identical branches: If you have multiple of the same branch, use prefixes: di- (2), tri- (3), tetra- (4), penta- (5), hexa- (6). (e.g., “hexamethyl” means there are six methyl branches attached to the main chain).
  • Alphabetize: List side chains alphabetically (e.g., ethyl comes before methyl. Ignore the di/tri prefixes when alphabetizing).
  • Punctuation: Use commas between numbers (e.g., 2,2) and hyphens between numbers and letters (e.g., 2-methyl). Example breakdown of “2,2,3,3,4,4-hexamethylpentane”: * Parent chain = “pentane” (5 carbons, all single bonds).
  • Branches = “hexamethyl” (6 separate -CH3 groups).
  • Locations = two on carbon 2, two on carbon 3, two on carbon 4. 3.7 Isomers
  • Structural Isomers: Molecules with the same molecular formula but a different structural arrangement of atoms.
  • Geometric (Cis-Trans) Isomers: Found in alkenes. Because atoms cannot freely rotate around a rigid C=C double bond, different spatial arrangements occur.
    • Cis isomer: The heavy functional/alkyl groups are on the same side of the double bond.
    • Trans isomer: The groups are on opposite sides of the double bond. 3.8 Hydrocarbon Reactions
  • Combustion (Alkanes, Alkenes, Benzene): Reacting with oxygen to release energy.
    • Complete: Excess O2. Produces CO2(g) + H2O(g) + immense heat.
    • Incomplete: Limited O2. Produces CO(g) (Carbon monoxide) + H2O(g) and sometimes C(s) (soot). Produces less energy.
  • Addition (Alkenes ONLY): The C=C double bond breaks and a new atom/group is added to each carbon atom. Fast reaction.
    • Common reagents: H2 (needs Pt/Ni catalyst), Cl2, Br2 (bromine water tests for alkenes - turns from orange to colorless), HCl, HBr.
  • Substitution (Alkanes & Benzene ONLY): A hydrogen atom is detached and substituted with a halogen (like Cl or Br). Very slow, requires UV Light to initiate.
  1. Exothermic vs. Endothermic & Enthalpy Enthalpy (H) is the stored chemical potential energy of a substance. Change in enthalpy is represented by “delta H”. During a reaction, energy is exchanged between the System (the chemical reaction) and the Surroundings (the container, environment).
  • Bond Breaking vs. Bond Making:
    • Breaking bonds requires an input of energy (Absorbs energy).
    • Making bonds releases energy. 4.1 Exothermic Reactions
  • Definition: Reactions that release energy (heat) into the surroundings.
  • Mechanism: The energy released making new bonds in products is greater than the energy absorbed breaking reactant bonds.
  • Enthalpy Change: Products have less enthalpy than reactants. Therefore, delta H is negative (-).
  • Observation: The surroundings get hotter. (e.g., Combustion, freezing). 4.2 Endothermic Reactions
  • Definition: Reactions that absorb energy (heat) from the surroundings.
  • Mechanism: The energy absorbed breaking reactant bonds is greater than the energy released forming product bonds.
  • Enthalpy Change: Products have more enthalpy than reactants. Therefore, delta H is positive (+).
  • Observation: The surroundings get colder. (e.g., Instant cold packs, melting). 4.3 Key Concepts & Energy Profile Diagrams
  • Activation Energy (Ea): The initial energy barrier that must be overcome to break reactant bonds so the reaction can start. Exists in both exo and endothermic reactions.
  • Law of Conservation of Energy: Energy is never created or destroyed. In an endothermic reaction, heat lost by surroundings = enthalpy gained by the system. In an exothermic reaction, enthalpy lost by system = heat released to surroundings.
  • Reversing a reaction: Flips the sign of delta H (e.g., from - to +) but the magnitude remains exactly the same.
  1. Past Exam Questions & Step-by-Step Solutions (Calculated using standard atomic masses: C=12.01, H=1.008, O=16.00, following stoichiometric methodology). Question 29: beta-carotene vs Retinal Percentage composition of carbon
  • beta-carotene (C40H56):
    • Molar mass = (40 x 12.011) + (56 x 1.008) = 536.888 g/mol
    • %C = (480.44 / 536.888) x 100 = 89.49%
  • Retinal (C20H28O):
    • Molar mass = (20 x 12.011) + (28 x 1.008) + 16.00 = 284.444 g/mol
    • %C = (240.22 / 284.444) x 100 = 84.45%
  • Answer: beta-carotene has a higher percentage composition of carbon. Number of retinal molecules from 100g carrot (containing 8.279 x 10^-3 g of beta-carotene)
  • Moles of beta-carotene = m/M = 8.279 x 10^-3 / 536.888 = 1.542 x 10^-5 mol
  • Molar Ratio: 1 beta-carotene produces 2 retinal molecules.
  • Moles of retinal = 2 x 1.542 x 10^-5 = 3.084 x 10^-5 mol
  • Molecules of retinal = n x NA = 3.084 x 10^-5 x (6.022 x 10^23) = 1.857 x 10^19 molecules Question 33: Antacid Neutralization
  • Moles of HCl neutralized by Al(OH)3 = 3 x n(Al(OH)3) = 7.692 x 10^-3 mol
  • Moles of HCl neutralized by Mg(OH)2 = 2 x n(Mg(OH)2) = 6.858 x 10^-3 mol
  • Total moles of HCl neutralized = 14.55 x 10^-3 mol
  • Mass of HCl = 14.55 x 10^-3 mol x 36.46 g/mol = 0.530 g (or 530 mg) Question 39: Petrodiesel vs Biodiesel Combustion of 56.3 kg (56,300 g)
  • Petrodiesel:
    • Mass CO2 = 3966.5 x 44.01 = 174.6 kg
    • Energy = (330.54 / 2) x 15803 kJ = 2.61 x 10^6 kJ
  • Biodiesel:
    • Mass CO2 = 3562.4 x 44.01 = 156.8 kg
    • Energy = 197.91 x 11368 kJ = 2.25 x 10^6 kJ Mass of waste cooking oil for 1 kg biodiesel
  • Molar ratio (Tripalmitin : Biodiesel) = 1 : 3
  • Mass of pure Tripalmitin = 1.172 x 807.294 = 946.1 g
  • Since oil is 68.1% Tripalmitin, Mass of waste oil = 946.1 / 0.681 = 1389 g (or 1.39 kg) Sem 1 2024 - Question 30 & 34 Percentage composition of sodium fluorosilicate (Na2SiF6)
  • %Na = 45.98 / 188.07 = 24.45%
  • %Si = 28.09 / 188.07 = 14.94%
  • %F = 114.00 / 188.07 = 60.62% Mass of fluorosilicic acid for 1 L of water (3.17 x 10^19 F ions per mL)
  • 1 L = 1000 mL. Total F ions = 3.17 x 10^19
  • Moles of F ions = (3.17 x 10^19) / (6.022 x 10^23) = 5.26 x 10^-5 mol
  • 1 molecule of H2SiF6 contains 6 F atoms.
  • Mass = 8.77 x 10^-6 x 144.11 = 1.26 x 10^-3 g = 1.26 mg Phosphoric acid extraction
  • Produced 1.83 kg (1830 g) of H3PO4 (M = 97.99 g/mol)
  • Ratio of H3PO4 to CaSO4 is 3:5. n(CaSO4) = (5/3) x 18.67 = 31.12 mol
  • Mass CaSO4 = 31.12 x 136.15 g/mol = 4237 g (or 4.24 kg) Sem 1 2023 - TNT & Biofuels Q35 (TNT)
  • Systematic IUPAC name for toluene: Methylbenzene.
  • Reaction Type: Substitution reaction. Hydrogen atoms on the benzene ring are detached and substituted by nitro (-NO2) groups.
  • Mass of TNT:
    • 385 kg HNO3 (M = 63.02 g/mol). n(HNO3) = 385000 / 63.02 = 6109 mol
    • Ratio HNO3 : TNT is 3 : 1. n(TNT) = 6109 / 3 = 2036 mol
    • M(TNT: C7H5N3O6) = 227.15 g/mol. Mass TNT = 2036 x 227.15 = 462,477 g = 462 kg
  • Thermodynamics: Exothermic. Energy released forming strong bonds in products (N2, H2, CO) is significantly greater than energy required to break bonds in TNT reactant.
  • Conservation of Energy: Total energy is conserved because heat released corresponds to equivalent loss of internal chemical potential enthalpy. Q38 (Biofuels)
  • Biofuel vs Fossil Fuel: Biofuel is derived from renewable organic biomass (e.g., plants). Fossil fuels formed over millions of years from dead organisms under pressure (non-renewable).
  • Air-fuel ratio for ethanol (C2H5OH): 1 mol ethanol (46.07 g) requires 3 mol O2 (96.00 g). Since air is 21% oxygen by mass, total mass of air required = 96.00 / 0.21 = 457.1 g. Air-fuel ratio = 457.1 / 46.07 = 9.92
  • Energy density of petrol: 42.9 MJ/kg x 0.7446 kg/L = 31.9 MJ/L. Petrol has the highest energy density.
  • Petrol composition: Petrol is a complex mixture of various hydrocarbons (C4 to C12), so it does not have a single exact chemical formula or molar mass.
  • DMF (C6H8O) Molar heat of combustion: M = 96.13 g/mol = 0.09613 kg/mol. Heat = 32.9 MJ/kg x 0.09613 kg/mol = 3.16 MJ/mol = 3160 kJ/mol Other Key Reaction Questions
  • Bromine test (Addition): Hex-1-ene + Br2 -> 1,2-dibromohexane. This is an Addition reaction.
  • Bunsen Burner (Butane): If 10,892 kJ of energy is produced by the butane canister, an equivalent amount of methane (CH4) must be burned. Methane releases 882 kJ/mol.
    • n(CH4) = 10892 / 882 = 12.35 mol
    • Mass of Methane = 12.35 x 16.04 g/mol = 198 g
  • Law of conservation of energy (Endothermic context): In an endothermic process (like dissolving ammonium nitrate), the heat energy lost from the surrounding environment is precisely equal to the increase in enthalpy (stored chemical energy) within the reacting system.