C15: Using Our Resources

What is a Life Cycle Assessment LCA?

An evaluation of the environmental impact of a product across all four main stages of its life.

What are the four main stages assessed in a Life Cycle Assessment LCA?

• Extracting and processing raw materials.

• Manufacturing and packaging the product.

• Use and operation of the product during its lifetime.

• Disposal at the end of its useful life, including transport and recycling.

Why are Life Cycle Assessments LCAs not purely objective?

• Quantifying water and energy use is easy, but assigning numerical values to pollutant impacts requires subjective judgements.

• Selective or abbreviated LCAs can be written to present a company's product in a positive light for advertising.

How does comparing plastic and paper shopping bags highlight trade-offs in Life Cycle Assessments?

• Plastic bags use crude oil (finite), but require less energy to make, are reusable, and lightweight to transport. However, they are non-biodegradable in landfills.

• Paper bags use timber (renewable), but require large amounts of energy and water to manufacture, are heavy to transport, and rarely reusable, though they biodegrade easily.

What are the environmental and economic benefits of recycling glass metals and polymers?

• Reduces the extraction of finite raw materials like crude oil and metal ores.

• Saves significant amounts of energy compared to extracting and refining new materials.

• Reduces landfill waste and decreases harmful greenhouse gas emissions from industrial processing.

How are metals and glass recycled in practice?

• Metals are melted down and recast into new products or added to iron during steel production.

• Glass bottles are crushed, melted, and remoulded into new glass containers.

What is corrosion and how does rusting differ from general corrosion?

• Corrosion is the destruction of materials by chemical reactions with substances in the environment.

• Rusting is specifically the corrosion of iron and steel, requiring both oxygen and water to occur.

What is the chemical reaction and word equation for the rusting of iron?

• Iron reacts with oxygen and water to form hydrated iron III oxide.

• Iron + Oxygen + Water -> Hydrated Iron III Oxide

Why does the corrosion of aluminium stop while iron continues to rust until destroyed?

Aluminium reacts with oxygen to form a thin, protective aluminium oxide layer that coats the surface and prevents further reaction, whereas rust flakes off iron and exposes fresh metal underneath.

How can corrosion be prevented using barrier methods?

Applying a physical coating to isolate the metal from water and oxygen, such as painting, greasing, plastic coating, or electroplating.

What is sacrificial protection and how does it prevent corrosion?

Attaching a more reactive metal (such as zinc or magnesium) to iron so the more reactive metal oxidises and corrodes first, sacrificing itself to protect the iron.

What is galvanising?

Coating iron or steel with a layer of zinc, which acts as both a protective barrier and sacrificial protection if scratched.

What is an alloy and why are alloys harder than pure metals?

• A mixture of a metal with small amounts of other elements.

• Atoms of different sizes disrupt the regular layer arrangement of the pure metal lattice, preventing layers from sliding over each other easily.

What are the compositions and uses of bronze brass and gold alloys?

• Bronze is an alloy of copper and tin used for statues, bells, and ship propellers.

• Brass is an alloy of copper and zinc used for musical instruments and door fittings.

• Gold used in jewellery is alloyed with silver, copper, and zinc for hardness; 24 carat is 100 percent pure gold, while 18 carat is 75 percent pure gold.

What are the differences between high carbon steel low carbon steel and stainless steel?

• Low carbon steel contains small amounts of carbon, making it soft and easily shaped for car bodies.

• High carbon steel contains more carbon, making it hard but brittle for tools and blades.

• Stainless steel contains chromium and nickel, making it hard and resistant to corrosion for cutlery and chemical pipes.

What are aluminium alloys used for and why?

Used in aircraft bodies and high-performance vehicles because they combine low density with high strength.

How are soda-lime glass and borosilicate glass made and how do they differ?

• Soda-lime glass is made by heating a mixture of sand, sodium carbonate, and limestone; it melts easily and is used for window panes.

• Borosilicate glass is made from sand and boron trioxide; it melts at higher temperatures and is heat-resistant for Pyrex cookware and lab glassware.

How are clay ceramics made and what are their key properties?

Made by shaping wet clay and baking it in a furnace; clay particles form strong covalent lattices making them hard, heat-resistant, and electrical insulators.

What is the structural difference between thermosoftening and thermosetting polymers?

• Thermosoftening polymers consist of individual polymer chains held by weak intermolecular forces that melt when heated and can be remoulded.

• Thermosetting polymers contain cross-links with strong covalent bonds between chains that do not melt on heating and decompose instead.

How do LDPE low density polyethene and HDPE high density polyethene differ?

• LDPE is produced under high pressure and trace oxygen, forming branched chains that cannot pack tightly, resulting in a flexible, low-density plastic.

• HDPE is produced using a catalyst at lower temperatures, forming straight unbranched chains that pack tightly together, resulting in a rigid, strong plastic.

What is a composite material and how is it structured?

A material consisting of a reinforcement matrix of fibers or fragments embedded in a binder or matrix material that binds them together.

What are common examples of composite materials and their uses?

• Fiberglass: Glass fibers embedded in a polymer matrix, used for kayaks and skis.

• Carbon fiber: Carbon nanotubes embedded in a polymer matrix, used in aerospace and sports equipment.

• Concrete: Aggregate mixture bound by cement, used for buildings and bridges.

• Wood: Cellulose fibers bound by a lignin matrix.

What is the Haber process and what chemical reaction takes place?

• Industrial process used to manufacture ammonia from nitrogen and hydrogen gases.

• Reaction is reversible: Nitrogen + Hydrogen

Where are the raw materials for the Haber process obtained?

• Nitrogen gas is extracted from the air by fractional distillation.

• Hydrogen gas is obtained by reacting methane natural gas with steam.

What are the industrial conditions used in the Haber process?

• Temperature of 450 degrees Celsius.

• Pressure of 200 atmospheres.

• Iron catalyst.

Why is 450 degrees Celsius used in the Haber process as a compromise temperature?

• Forward reaction is exothermic, so lower temperatures shift equilibrium right to increase yield, but make the reaction rate extremely slow.

• 450 degrees Celsius provides a fast rate of reaction while maintaining an acceptable yield of ammonia.

Why is 200 atmospheres used in the Haber process as a compromise pressure?

• Higher pressure shifts equilibrium right to increase yield and speeds up rate, but building and maintaining extremely high-pressure equipment is dangerously expensive.

• 200 atmospheres balances high yield and safety with manageable operating costs.

How is ammonia gas separated and recycled in the Haber process?

• Reaction mixture is cooled in a condenser so ammonia gas liquefies and is piped away.

• Unreacted nitrogen and hydrogen gases are recycled back into the reactor vessel, ensuring zero wasted raw materials.

What are NPK fertilisers?

Formulations containing compounds of nitrogen N, phosphorus P, and potassium K used to improve crop growth and yield.

How are nitrogen compounds supplied in NPK fertilisers?

Ammonia produced in the Haber process is reacted with nitric acid to produce ammonium nitrate salt: NH3 + HNO3 -> NH4NO3.

How are potassium compounds supplied in NPK fertilisers?

Potassium chloride and potassium sulfate salts are mined directly from underground deposits and used without chemical processing because they are already soluble.

How are phosphate compounds supplied in NPK fertilisers?

• Phosphate rock is mined but insoluble, so it must be treated with acids to produce soluble salts.

• Treated with nitric acid to form phosphoric acid and calcium nitrate.

• Treated with sulfuric acid to form single superphosphate (mixture of calcium phosphate and calcium sulfate).

• Treated with phosphoric acid to form triple superphosphate (calcium phosphate).

How does the industrial production of ammonium nitrate compare to its laboratory preparation?

• In industry, concentrated ammonia gas reacts with concentrated nitric acid in a continuous, highly exothermic, large-scale process using high temperatures.

• In the laboratory, dilute solutions are reacted by titration on a small batch scale at room temperature, then crystallised slowly using a Bunsen burne