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Flashcards · 9202 · Topic 10
Organic chemistry flashcards
26 cards on Topic 10, subtopics 3.10.1 to 3.10.3. Pick a subtopic or study them all.
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3.10.1 Carbon compounds as fuels
- Crude oil vs the hydrocarbons in it
- Crude oil is a mixture; each hydrocarbon in it is a compound.
- How does fractional distillation separate crude oil?
- The oil is vaporised and fed into a column that is hotter at the base than the top. Each vapour rises until it reaches a level cooler than its boiling point, then condenses and is tapped off. It is continuous.
- Saturated vs unsaturated
- Saturated: only single C–C bonds. Unsaturated: at least one C=C.
- General formulae of alkanes and alkenes, and the formula of the alkane with 20 carbons
- Alkanes: CₙH₂ₙ₊₂. Alkenes: CₙH₂ₙ. C₂₀H₄₂
- How do boiling point, viscosity and flammability change as hydrocarbon molecules get bigger?
- Boiling point rises, viscosity increases and flammability decreases — so short-chain hydrocarbons make better fuels.
- Complete and incomplete combustion of ethane
- Complete: 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O. Incomplete (oxygen short): CO or soot forms, e.g. 2C₂H₆ + 5O₂ → 4CO + 6H₂O. Water still forms.
- Acid rain vs global dimming vs climate change: the pollutants
- Acid rain: SO₂ (sulfur in the fuel) and NOₓ (air reacting at high temperature). Global dimming: particulates. Climate change: CO₂.
- Making ethanol: hydration of ethene vs fermentation
- Hydration: C₂H₄ + H₂O → C₂H₅OH; phosphoric acid, about 300 °C, high pressure; fast, continuous, pure; non-renewable raw material. Fermentation: yeast enzymes, 20–35 °C; slow, batch, dilute; renewable sugar.
- Biofuels: renewability, land use and carbon footprint
- Renewable: crops regrow. Land use: fuel crops can take land from food or lead to forest clearing. Carbon footprint: growing plants absorb CO₂, but farming, processing and transport add emissions, so it is reduced, not removed.
- Cracking: what it is and the two methods
- Thermal decomposition of large hydrocarbons into smaller alkanes and alkenes. Vaporise them, then pass over a hot catalyst, or mix with steam and heat to a very high temperature.
- Fractional distillation vs cracking
- Fractional distillation: physical separation by boiling point. Cracking: a chemical reaction that breaks molecules.
- Required practical: testing for a C=C double bond
- Shake with bromine water. Alkene: orange → colourless. Alkane: stays orange.
3.10.2 Synthetic and naturally occurring polymers
- Monomer and polymer
- Monomer: a small molecule that can join with many others. Polymer: a very large molecule formed from many monomers joined together.
- Addition polymerisation of an alkene: what happens?
- One bond of each C=C opens and the freed bonds link neighbouring monomers into a long chain. Nothing else is made. Ethene → poly(ethene); propene → poly(propene).
- Give the monomer of the chain unit –(CHF–CF₂)n–
- CHF=CF₂ — remove the bonds through the brackets and the n, and put a double bond between the two carbons.
- LD vs HD poly(ethene)
- Same monomer, different conditions and catalysts. LD: highly branched chains, loose packing, weaker forces — flexible, lower density. HD: mainly unbranched, close packing, stronger forces — rigid, higher density.
- Thermosoftening vs thermosetting polymers
- Thermosoftening: separate chains held by weak intermolecular forces; soften and melt on heating. Thermosetting: chains joined by strong covalent cross-links; do not melt.
- Why are non-biodegradable polymers a problem, and what does biodegradable mean?
- Biodegradable: can be broken down by microbes. Many polymers are not, so they persist in landfill and as litter that harms wildlife.
- Polymer + cornstarch bag vs biodegradable plastic made from cornstarch
- Polymer + cornstarch: microbes digest the starch so the bag falls apart, but polymer fragments may remain. Cornstarch plastic: the whole material can be broken down by microbes.
3.10.3 Organic compounds – their structure and reactions
- Functional groups of alcohols, carboxylic acids and esters
- Alcohols: –OH (names end -ol). Carboxylic acids: –COOH (end -oic acid). Esters: –COO– (two words, the second ending -oate).
- Alcohols: effect on water, reaction with sodium, and combustion
- Dissolve to give a neutral solution (pH 7). With sodium: fizzing, hydrogen given off. Burn completely to carbon dioxide and water.
- Complete combustion of ethanol
- C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
- Two ways to oxidise ethanol to ethanoic acid
- A chemical oxidising agent (e.g. acidified potassium dichromate), or microbial action using oxygen from the air — why opened wine turns sour. Ethanoic acid is the main acid in vinegar.
- Ethanoic acid + potassium carbonate: balanced equation
- 2CH₃COOH + K₂CO₃ → 2CH₃COOK + H₂O + CO₂ (fizzing; the gas turns limewater milky).
- Why does 0.1 mol/dm³ ethanoic acid have a higher pH than 0.1 mol/dm³ nitric acid?
- Ethanoic acid is a weak acid: it only partly ionises (CH₃COOH ⇌ CH₃COO⁻ + H⁺), so it gives fewer H⁺ ions. Nitric acid ionises completely.
- Making ethyl ethanoate, and two properties and uses of esters
- Ethanol + ethanoic acid ⇌ ethyl ethanoate + water, with an acid catalyst. Esters are volatile with distinctive smells, used in flavourings and perfumes.