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Flashcards · J248 · Topic 6

Topic C6 – Global Challenges flashcards

29 cards on Topic 6, subtopics C6.1 to C6.3. Pick a subtopic or study them all.

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C6.1 Improving Processes and Products

Ore
Rock from which a metal compound can be extracted at a profit.
Which metals are extracted by heating with carbon, and which by electrolysis?
Metals below carbon in the reactivity series (e.g. iron, zinc, copper, lead): heat the oxide with carbon, which is the reducing agent. Metals above carbon (e.g. aluminium): electrolysis, which needs large amounts of electricity.
Extracting aluminium: electrolyte and electrode half equations
Aluminium oxide dissolved in molten cryolite (lower operating temperature). Cathode: Al³⁺ + 3e⁻ → Al. Anode: 2O²⁻ → O₂ + 4e⁻; the oxygen burns the carbon anodes to CO₂, so they are replaced.
Bioleaching vs phytoextractionHigher
Bioleaching: bacteria produce a leachate of metal ions from low-grade ore. Phytoextraction: plants absorb metal ions and are burned, leaving metal-rich ash. Both are low energy but slow; the metal is then got by scrap iron displacement or electrolysis.
Haber process conditions, and why the pressure is about 200 atmHigher
N₂ + 3H₂ ⇌ 2NH₃ (exothermic): iron catalyst, about 450 °C, about 200 atm. Fewer gas molecules on the right, so high pressure helps yield and rate; higher still would cost too much.
Contact process: equation and conditionsHigher
2SO₂ + O₂ ⇌ 2SO₃ (exothermic): vanadium(V) oxide catalyst, about 450 °C, pressure close to atmospheric (the yield is already high).
Fertilisers: the three elements, and one property every fertiliser compound needs
Nitrogen, phosphorus and potassium (NPK). The compounds must be soluble.
The four stages of a life-cycle assessment
Raw materials and manufacture; use; transport; disposal (landfill, incineration or recycling).
Composition of brass, bronze and solder
Brass: copper + zinc. Bronze: copper + tin. Solder: tin + lead (or tin with small amounts of copper or silver).
What does rusting need, and how does sacrificial protection work?
Oxygen and water. A more reactive metal (zinc or magnesium) attached to the iron oxidises first, in place of the iron. Galvanising gives a barrier and sacrificial protection.

C6.2 Organic Chemistry

Homologous series
A family with one general formula and the same functional group; each member adds CH₂.
General formulae of alkanes, alkenes, alcohols and carboxylic acids
Alkane CₙH₂ₙ₊₂. Alkene CₙH₂ₙ. Alcohol CₙH₂ₙ₊₁OH. Carboxylic acid CₙH₂ₙ₊₁COOH.
How does bromine water distinguish an alkene from an alkane?
The alkene adds bromine across the C=C, turning bromine water from orange to colourless. An alkane leaves it orange.
Oxidising an alcohol: reagent, observation and product
Warm with acidified potassium manganate(VII): purple → colourless. Ethanol → ethanoic acid.
Monomer and repeat unit of PTFE
Monomer: tetrafluoroethene, CF₂=CF₂. Repeat unit: –[CF₂–CF₂]– with n outside the brackets. The C=C opens to C–C.
Condensation polymers: what the monomers need, and the two typesHigher
Each monomer has two functional groups, and a small molecule (usually water) is released at each link. Polyester: diol + dicarboxylic acid. Polyamide (nylon): diamine + dicarboxylic acid.
Monomers of DNA, starch and cellulose, and proteins
DNA: four nucleotides (bases adenine, thymine, cytosine, guanine). Starch and cellulose: sugars (glucose). Proteins: amino acids.
Fractions of crude oil, from the top of the column to the bottom
Refinery gases, petrol, kerosene, diesel, fuel oil, bitumen. Bigger molecules have stronger intermolecular forces and higher boiling points, so they are collected lower.
Cracking: products, conditions and reasons
Long alkanes → shorter alkanes + alkenes. Vapour over a hot catalyst (zeolite at about 500 °C in industry; aluminium oxide in the lab). Demand for short-chain fuels exceeds supply, and alkenes make polymers.
A chain of poly(butene) has Mr 56 000. How many C₄H₈ monomers joined?
Mr of C₄H₈ = 48 + 8 = 56. 56 000 ÷ 56 = 1000.

C6.3 Interpreting and Interacting with Earth Systems

Earth's first atmosphere: thought composition and source
Mainly carbon dioxide and water vapour, some nitrogen, possibly a little methane and ammonia, almost no oxygen. Released by volcanic outgassing.
How the early atmosphere changed
Water vapour condensed to form oceans; CO₂ dissolved and was locked into carbonate rocks; photosynthesis removed more CO₂; carbon was stored in fossil fuels; unreactive nitrogen built up.
Composition of dry air today
About 78% nitrogen, 21% oxygen, 0.9% argon and 0.04% carbon dioxide.
How did oxygen build up in the atmosphere?
Cyanobacteria, then algae and plants, photosynthesised. Early oxygen reacted with dissolved iron (banded iron formations), then built up in the air; an ozone layer formed. It took billions of years.
How do greenhouse gases keep the Earth warm?
Mostly short-wavelength sunlight warms the surface, which emits longer-wavelength infrared. Greenhouse gases absorb the infrared and re-emit it in all directions, so less energy escapes to space.
Why does a correlation between CO₂ and temperature not prove a human cause on its own?
Correlation is not causation: a mechanism is needed. Natural factors also change climate, past data come from proxies with larger error, and models simplify complex systems.
Convert 0.038% carbon dioxide into ppm
1% = 10 000 ppm, so 0.038 × 10 000 = 380 ppm.
How carbon monoxide, sulfur dioxide and oxides of nitrogen form, and their problems
CO: incomplete combustion; toxic, no colour or smell. SO₂: sulfur impurities in fuels burn; acid rain. NO and NO₂: nitrogen from the air reacts at high engine temperatures; acid rain and breathing problems.
How is fresh surface water made potable, and which source needs most energy?
Sedimentation → filtration (sand, gravel) → sterilisation (chlorine, ozone or UV). Salt water needs most energy: desalination by distillation or reverse osmosis.

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