Everything we use in our daily lives, from the electricity that powers our phones to the clothes we wear, comes from the Earth’s resources. How we manage these resources is one of the most important challenges facing humanity.

The Earth’s Resources 

Humans use natural resources to provide for all their basic needs, including warmth, shelter, food, and transport. These resources come from the Earth, the sea, and the air. Natural products, often supported by agriculture, give us essentials like food, timber, and clothing.

Resources can be classified into two main types:

• Renewable Resources: These can be replaced as quickly as we use them. Examples include timber, fresh water, and food.

• Finite (Non-Renewable) Resources: These are used up much faster than they can be formed and will eventually run out. Examples include fossil fuels, nuclear fuels, metals, and minerals.

Exam Tip: You must be able to distinguish between renewable and finite resources and give examples of each. Remember, ‘finite’ means there is a limited amount.

Sustainable Development 

Chemistry plays a vital role in sustainable development. This is a key idea for managing our planet’s resources responsibly.

The definition of sustainable development is:

“Development that meets the needs of current generations without compromising the ability of future generations to meet their own needs.”

In simple terms, it means living our lives and using resources in a way that doesn’t ruin things for people in the future. The goal is to balance living comfortably now with preserving the environment and ensuring resources will still be available for generations to come. Chemists work to find ways to manufacture products that use less energy, create less waste, and have a minimal impact on the environment.

Exam Tip: The definition of sustainable development is often a one or two-mark question in the exam. It’s a good idea to memorise it. The key phrase is “meeting the needs of the present without compromising the needs of the future.”

Water is essential for life, but not all water is safe to drink. Potable water is the scientific term for water that is safe for humans to drink.

Potable Water vs. Pure Water

It’s important to know the difference between potable water and pure water.

• Potable Water: Is safe to drink but is not chemically pure. It contains dissolved substances, like salts and minerals, which are often what give water its taste.

• Pure Water: Contains only H₂O molecules with nothing dissolved in it. An example is distilled water.

To be considered potable, water must have:

• Sufficiently low levels of dissolved salts.

• A pH between 6.5 and 8.5.

• No bacteria or other harmful microbes.

Exam Tip: A common exam question asks for the difference between pure water and potable water. Remember: potable water is safe to drink and contains dissolved solids, whereas pure water contains only H₂O molecules.

Making Water Potable in the UK

In the UK, most of our drinking water comes from fresh water sources like rivers, lakes, and underground aquifers. This water must be treated to make it potable. The process involves two main stages: filtration and sterilisation.

1. Filtration: The water is first passed through a wire mesh to remove large objects like twigs. It is then passed through beds of sand and gravel. This filters out any solid particles, grit, and some microbes.

2. Sterilisation: After filtration, the water is sterilised to kill any remaining harmful bacteria or microbes. Common sterilising agents include:

   • Chlorine

   • Ozone

   • Ultraviolet (UV) light

Exam Tip: You must remember the two key stages of treating fresh water: filtration (to remove solids) and sterilisation (to kill microbes).

Desalination: Making Potable Water from Seawater

In places where fresh water is limited, it is necessary to remove the salt from seawater in a process called desalination. There are two main methods:

• Distillation: Seawater is boiled, and the steam (pure water) is collected and condensed, leaving the salt behind.

• Reverse Osmosis: High pressure is used to force seawater through a special membrane that only allows water molecules to pass through, leaving the salt behind.

The biggest problem with both of these methods is that they require large amounts of energy, which makes them very expensive.

Exam Tip: The major disadvantage of desalination is its high energy requirement and cost. This is a frequently tested point.

Urban lifestyles and industrial processes produce vast quantities of waste water that must be treated before it can be safely returned to the environment. Different types of waste water, such as sewage, agricultural run-off, and industrial discharge, require specific treatments to remove organic matter, harmful microbes, and dangerous chemicals.

The Stages of Sewage Treatment

Treating sewage is a multi-stage process designed to separate solids from liquids and use bacteria to break down harmful substances.

1. Screening and Grit Removal

The first stage is a physical process.

• Screening: Waste water is passed through a large screen or mesh. This removes large floating objects like wood and plastic bags.

• Grit Removal: The water is then allowed to stand so that smaller solid particles like grit can settle out.

2. Sedimentation

In this stage, the remaining solid and liquid parts are separated.

• The water is left in large settlement tanks.

• Heavier solid particles sink to the bottom, forming a layer of sewage sludge.

• The lighter liquid layer, known as effluent, remains on top.

Exam Tip: You need to know the names of the two substances produced during sedimentation: the solid sewage sludge and the liquid effluent.

Treating the Sludge and Effluent

The sludge and effluent are treated separately using biological processes.

3. Anaerobic Digestion of Sludge

The sewage sludge is broken down by bacteria in the absence of oxygen.

• This anaerobic digestion process produces methane gas. This methane is often captured and burned as a fuel to generate electricity, which can be used to power the treatment plant.

• The remaining dried, sterilised sludge is rich in nutrients and is often used as a fertiliser for farmland.

4. Aerobic Biological Treatment of Effluent

The liquid effluent is treated by bubbling air through it to encourage bacteria to break down any remaining organic matter and harmful microbes in the presence of oxygen. This process produces carbon dioxide.

After this stage, the treated water is safe enough to be discharged back into rivers or the sea.

Exam Tip: A common point of confusion is the two types of biological treatment. Remember:

Sludge is treated by anaerobic digestion (no oxygen), producing methane.

Effluent is treated by aerobic digestion (with oxygen), producing carbon dioxide.

The Earth’s supply of high-grade metal ores is finite and running low. For metals like copper, which are in high demand, this means we need to find new, more sustainable ways to extract them from low-grade ores (ores that contain only a small amount of the desired metal). Two modern, biological methods for this are phytomining and bioleaching.

These methods are often better for the environment because they avoid the need for traditional large-scale mining, which involves digging up and disposing of huge amounts of rock.

Phytomining 

Phytomining uses plants to absorb metal compounds from the soil.

The Process:

1. Absorption: Plants are grown in soil that contains the low-grade ore. As they grow, they absorb the metal compounds through their roots and concentrate them in their leaves and shoots.

2. Harvesting and Burning: The plants are then harvested, dried, and burned in a furnace.

3. Ash Collection: The metal compounds are collected from the ash that is left behind.

Exam Tip: Remember the sequence for phytomining: Plants absorb metal ⟶ Plants are burned ⟶ Metal is extracted from the ash.

Bioleaching 

Bioleaching uses bacteria to separate metals from their ores.

The Process:

1. Bacterial Action: Certain types of bacteria are mixed with the low-grade ore. These bacteria feed on the ore, breaking down the metal compounds.

2. Leachate Production: As the bacteria break down the ore, they produce a solution containing the dissolved metal ions. This solution is called a leachate.

Exam Tip: For bioleaching, think Bacteria ⟶ Leachate. The key is that the bacteria make the insoluble metal compound soluble, allowing it to be collected in a solution.

Extracting the Metal

Both phytomining (from the ash) and bioleaching (from the leachate) produce a solution containing the dissolved metal ions. To get the pure metal from this solution, a final extraction step is needed. For copper, this is usually done using:

1. Displacement: Scrap iron is added to the solution. Since iron is more reactive than copper, it displaces the copper ions, causing pure copper metal to form.

2. Electrolysis: An electric current is passed through the solution, causing the pure copper metal to be deposited on the negative electrode.

The displacement reaction involves the following key species:

Exam Tip: Be prepared to evaluate these biological methods. Their main advantage is less damage to the environment compared to traditional mining. Their main disadvantage is that they are very slow.

To understand the true environmental cost of a product, we need to look at its entire lifespan, from creation to disposal. This “cradle-to-grave” analysis is called a Life Cycle Assessment (LCA).

What is a Life Cycle Assessment?

A Life Cycle Assessment (LCA) evaluates the environmental impact of a product at every stage of its life. The assessment is typically broken down into four key stages.

1. Getting the Raw Materials: This includes the impact of extracting the materials from the Earth (e.g., mining or drilling), which uses a lot of energy and can cause pollution, and processing them into usable forms.

2. Manufacturing and Packaging: This stage looks at the energy used and pollution created during the production of the product and its packaging. Chemical reactions used in manufacturing can also produce waste products that need to be disposed of.

3. Using the Product: This assesses the environmental impact during the product’s lifetime. For example, a car’s LCA would include the pollution from burning petrol , and a fertiliser’s LCA would include the impact of it washing into rivers.

4. Product Disposal: This covers what happens when the product is thrown away. It includes the energy needed to transport waste and the pollution caused by either sending it to landfill or incinerating (burning) it.

Exam Tip: You must be able to recall the four main stages of an LCA: raw material extraction, manufacturing, use, and disposal.

Problems and Limitations of LCAs

While LCAs are very useful, they are not always straightforward.

• Quantification Issues: It’s relatively easy to measure quantifiable data like water usage, energy consumption, and the mass of waste produced. However, it’s much harder to assign a numerical value to the harmful effects of pollutants, which requires value judgements.

• Not Purely Objective: Because of these value judgements, an LCA is not a purely objective process.

• Bias and Misuse: The person carrying out the assessment can introduce bias. Companies can also perform selective LCAs, leaving out certain stages to make their product seem more environmentally friendly for advertising purposes.

Exam Tip: When asked to evaluate the use of LCAs, a good answer will mention their benefits in assessing overall impact but also highlight the major limitation: they can be biased and are not purely objective because some environmental effects are difficult to quantify.

Comparative LCA: Plastic vs. Paper Bags

LCAs are often used to compare different products that do the same job. Let’s compare a plastic bag and a paper bag.

This comparison shows there isn’t always a simple answer. While the raw material for paper bags is more sustainable, their manufacturing can be very energy-intensive, and they are less likely to be reused than a plastic bag.

To manage the Earth’s finite resources sustainably, we follow three key principles known as the “3 Rs”: Reduce, Reuse, and Recycle. Implementing these strategies helps to decrease the use of limited resources and energy, which in turn reduces waste and our overall environmental impact.

Reduce

The simplest and most effective strategy is to reduce the amount of resources we consume in the first place.

• Reducing our reliance on processes like quarrying and mining is important because they cause significant environmental damage and use a lot of energy, often from fossil fuels.

• A real-world example is the 80% drop in the use of plastic carrier bags in the UK after a 5p charge was introduced, showing how small changes can have a big environmental impact.

Reuse

Some products can be reused for the same purpose multiple times, which saves the energy and materials needed to make new ones.

• Glass bottles are a great example. They can simply be washed, sterilised, and refilled, which uses much less energy than making new bottles from raw materials.

Exam Tip: When asked for an example of reusing, glass bottles are a perfect choice. Remember to state that the main benefit is saving the energy required for manufacturing.

Recycle

Recycling is the process of converting waste materials into new products. This is vital for materials like metals, glass, and most plastics, which are made from finite raw materials.

Recycling Metals

Recycling metals is much better for the environment than extracting them from their ores.

• Process: Metals are recycled by being melted down and then recast or reformed into new products.

• Benefits: This process uses far less energy than mining and extracting new metals. For instance, scrap steel can be added to the iron from a blast furnace, which reduces the amount of iron that needs to be extracted from its ore.

Recycling Glass

Glass that can’t be reused is recycled.

• Process: The glass is separated by colour, then crushed, melted, and remoulded into new glass products.

Overall Benefits of Recycling:

• Reduces the amount of waste sent to landfill sites.

• Conserves the Earth’s finite resources of metals and minerals.

• Saves energy compared to extraction and manufacturing.

• Creates employment.

Exam Tip: A common exam question asks you to evaluate the pros and cons of recycling. The main advantage is saving energy and finite resources. A disadvantage is that collecting, transporting, and sorting the waste materials also requires energy.

Corrosion is the general term for the destruction of materials by chemical reactions with substances in their environment. The most familiar example of corrosion is rusting, which specifically affects iron and its alloys, like steel.

What is Rusting?

Rusting is the corrosion of iron. For iron to rust, two substances must be present:

• Oxygen (from the air)

• Water

An experiment using three iron nails can prove this. A nail will only rust in a test tube that contains both air and water. A nail in a tube with only air (kept dry with calcium chloride) or in a tube with only boiled water (to remove air, with a layer of oil on top to stop more air dissolving) will not rust.

Rusting is a redox reaction where iron reacts with oxygen and water to form hydrated iron(III) oxide, which we call rust.

• Oxidation: Iron atoms lose electrons. (Fe ⟶ Fe³⁺ + 3e⁻)

• Reduction: Oxygen atoms gain electrons.

Unlike aluminum, which forms a tough, protective layer of aluminum oxide that prevents further corrosion, rust is flaky and breaks off easily. This exposes fresh iron underneath, which can then also rust, eventually destroying the entire object.

The key molecules and ions involved in the rusting of iron are:

Exam Tip: You must remember that both oxygen and water are required for rusting. Questions often ask you to interpret the results of the three-test-tube experiment.

How to Prevent Corrosion

We can stop rust from forming by preventing oxygen and water from reaching the iron. There are two main approaches.

1. Barrier Methods

These methods involve putting a physical barrier between the iron and the environment.

• Painting: Creates a protective layer. Ideal for large structures like bridges and ships.

• Greasing/Oiling: Used for moving parts, like a bike chain, to keep water out.

• Electroplating: Uses electrolysis to coat the iron with a thin layer of a less reactive metal, like chromium, which doesn’t corrode.

2. Sacrificial Protection

This clever method involves using a more reactive metal to protect the iron.

• Mechanism: The more reactive metal will corrode (be oxidized) in preference to the iron. The more reactive metal is “sacrificed” to save the iron.

• Example: Large blocks of a reactive metal like zinc or magnesium are attached to the steel hulls of ships. The zinc or magnesium corrodes away over time, leaving the steel hull intact.

Galvanising is a common process where an object, like a steel bucket or nail, is coated in a layer of zinc. This acts as a barrier, but if the surface is scratched, the zinc will also provide sacrificial protection to the exposed iron.

Exam Tip: When explaining sacrificial protection, you must state that the metal used is more reactive than iron. This is the key reason it works.

Most of the “metals” we encounter and use every day are not pure elements but are actually alloys. Pure metals are often too soft or reactive for many applications, so we mix them with other elements to enhance their properties.

An alloy is a mixture of a metal with at least one other element (which can be another metal or a non-metal) to improve its properties.

Common Alloys and Their Uses

You need to know the composition of several key alloys:

• Bronze: An alloy of copper and tin.

• Brass: An alloy of copper and zinc.

• Gold Alloys: Pure gold (24 carat) is very soft. For jewellery, it is alloyed with silver, copper, and zinc to make it harder and more durable. The purity of gold is measured in carats; for example, 18-carat gold is 75% pure gold.

• Aluminium Alloys: These are known for their low density, making them useful in applications where light weight is important, such as in aircraft construction.

Below are some of the key elemental components used to make common alloys.

Exam Tip: A common exam question involves calculating the mass of a pure metal in an alloy object given its total mass and purity. For example, to find the mass of gold in an 18-carat (75% gold) ring that weighs 10g, you would calculate 75% of 10g (0.75 x 10 = 7.5g).

Steels: Alloys of Iron

Steels are alloys of iron that contain specific amounts of carbon and sometimes other metals. Changing the composition dramatically changes the properties of the steel.

• High Carbon Steel: Is very strong but brittle. It is used for tools like drill bits.

• Low Carbon Steel: Is softer and more easily shaped. It is used for car bodies.

• Stainless Steel: Is an alloy of iron with chromium and nickel. It is hard and, most importantly, resistant to corrosion (rusting). It is used for cutlery and surgical instruments.

Exam Tip: You must be able to recall the properties and uses of the different types of steel. A good way to remember is: High Carbon = Hard but Brittle, Low Carbon = Soft and Shapeable, Stainless = Hard and Rust-Resistant.

When choosing a material for a specific job, its properties must match the requirements of that job. This lesson explores three important classes of materials: ceramics, polymers, and composites.

Ceramics

Ceramics are non-metallic solids that are hard, brittle, and have high melting points. They are excellent thermal and electrical insulators.

• Clay Ceramics: Made by shaping wet clay and then heating it in a furnace. Clay ceramics like bricks and potteryare very hard and can withstand high temperatures and pressures.

• Glass: Most of the glass we use is soda-lime glass, made by heating a mixture of sand, sodium carbonate, and limestone. It is transparent but melts at a relatively low temperature. Borosilicate glass is made from sand and boron trioxide. It has a much higher melting point, making it ideal for ovenware and laboratory glassware.

The key components for making different types of glass include:

Exam Tip: Remember the difference between the two main types of glass. Borosilicate glass has a higher melting point, which is why it’s used for cookware that goes in the oven.

Polymers

Polymers are very long molecules made from many small, repeating units called monomers. The properties of a polymer depend on which monomer it’s made from and the conditions used to make it. There are two main types of polymers based on how they respond to heat.

• Thermosoftening Polymers: These polymers consist of long chains held together by weak intermolecular forces. They melt when heated and can be remoulded into new shapes, making them easy to recycle. They are typically flexible and are used for products like plastic bags and bottles.

• Thermosetting Polymers: These polymers have strong cross-links between their chains. These cross-links prevent the chains from moving, so the polymer does not melt when heated (it just chars at very high temperatures). They are rigid, hard, and are used for things like plug sockets and electrical casings.

A great example is poly(ethene), which can be made in two forms from the same monomer, ethene:

• Low-Density Poly(ethene) (LDPE): Made using high pressure and temperature. It is flexible and used for plastic bags.

• High-Density Poly(ethene) (HDPE): Made using a catalyst at lower temperature and pressure. It is more rigid and is used for things like milk crates and pipes.

Exam Tip: The key difference between the two types of polymer is the cross-links. Thermosetting polymers have them (making them rigid and non-melting), while thermosoftening polymers do not (making them meltable and recyclable).

Composites

Composites are materials made by combining two or more substances to create a new material with improved properties. They consist of a matrix (or binder) and a reinforcement (fibres or fragments).

Exam Tip: You should be able to state that a composite is made of a matrix and a reinforcement and give an example, like carbon fibre, explaining how its properties (strong and lightweight) make it suitable for a specific use (like a racing car).

The Haber process is one of the most important industrial chemical reactions in the world. It is the process used to manufacture ammonia (NH₃), a vital compound needed to produce nitrogen-based fertilisers that help grow the food required to feed the global population.

Raw Materials and Reaction

The Haber process combines two gases, nitrogen and hydrogen, to make ammonia.

• Nitrogen (N₂): Is obtained from the air, which is approximately 78% nitrogen.

• Hydrogen (H₂): Is typically produced from natural gas (methane) or other fossil fuels.

The reaction is reversible, which is key to understanding how the process works.

Word Equation: Nitrogen + Hydrogen ⇌ Ammonia

Balanced Symbol Equation: N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

Reaction Conditions

To make the reaction happen efficiently, a specific set of conditions is used inside a reaction vessel. The purified nitrogen and hydrogen gases are passed over an iron catalyst.

Exam Tip: You must remember the raw materials and their sources (nitrogen from air, hydrogen from natural gas) and the three specific conditions used in the Haber process: an iron catalyst, 450 °C, and 200 atm.

The Industrial Process

The process is designed to be continuous to maximise the production of ammonia.

1. Reaction: Nitrogen and hydrogen gases are passed over the iron catalyst at 450 °C and 200 atm. Some of the gases react to form ammonia, but because the reaction is reversible, a lot of unreacted nitrogen and hydrogen remains.

2. Cooling & Separation: The mixture of gases flows into a condenser and is cooled. Ammonia has a higher boiling point than nitrogen and hydrogen, so it liquefies and is removed from the bottom.

3. Recycling: The unreacted nitrogen and hydrogen remain as gases. They are recycled back into the reaction vessel to be passed over the catalyst again. This ensures the raw materials are not wasted.

The molecules involved in the Haber process reaction are shown below.

Exam Tip: The separation and recycling steps are crucial for the efficiency of the process. Remember that the separation works because ammonia liquefies on cooling while the reactants do not.

Compromise Conditions (HT only)

The conditions used in the Haber process are a compromise to balance the rate of reaction, the percentage yield, and the cost.

Temperature: 450 °C

• Yield: The forward reaction (N₂ + 3H₂ ⟶ 2NH₃) is exothermic. According to Le Chatelier’s principle, a low temperature would favour the forward reaction, giving a high yield of ammonia.

• Rate: However, a low temperature would make the reaction too slow.

• Compromise: 450 °C is a compromise temperature that is high enough to get a fast rate of reaction but low enough to still get a reasonable percentage yield.

Pressure: 200 atm

• Yield: There are 4 moles of gas on the reactant side (1 N₂ + 3 H₂) and only 2 moles of gas on the product side (2 NH₃). According to Le Chatelier’s principle, a high pressure will favour the side with fewer moles, shifting the equilibrium to the right and giving a high yield of ammonia.

• Rate: High pressure also increases the rate of reaction as the gas molecules are closer together and collide more frequently.

• Compromise: Very high pressures are expensive to generate and require strong, expensive equipment to contain safely. 200 atm is a compromise pressure that gives a good yield and rate without being excessively costly or dangerous.

To feed the world’s growing population, farmers need to ensure high crop yields. Fertilisers are substances added to the soil to provide essential nutrients that plants need to grow well. The most important of these are compounds containing nitrogen, phosphorus, and potassium.

What are NPK Fertilisers? 

NPK fertilisers are specially designed formulations that contain salts of the three essential elements for plant growth: Nitrogen (N), Phosphorus (P), and Potassium (K). They are used to improve agricultural productivity by replenishing these nutrients in the soil. Different crops and soils require different ratios of these elements, so NPK fertilisers are produced with specific percentages to meet these needs.

Industrial Production of NPK Fertilisers

Making NPK fertilisers is a large-scale industrial process that combines raw materials from different sources.

Nitrogen (N) Compounds

The source of all nitrogen in these fertilisers is ammonia (NH₃), which is produced in the Haber process. The ammonia is then used to make other nitrogen-containing compounds:

• It is reacted with acids to produce ammonium salts, such as ammonium sulfate.

• It is used to produce nitric acid, which can then be used to make other fertilisers like ammonium nitrate.

Potassium (K) and Phosphorus (P) Compounds

These elements are obtained from the ground by mining.

• Potassium is mined as potassium chloride and potassium sulfate salts, which are soluble in water and can be used directly.

• Phosphorus is mined as phosphate rock. However, phosphate rock is insoluble in water, so it cannot be used directly as a fertiliser because plants cannot absorb it through their roots.

Exam Tip: A very common exam question asks why phosphate rock cannot be used directly as a fertiliser. The answer is because it is insoluble in water, so plants cannot absorb the phosphate ions.

Treating Phosphate Rock

To make the phosphorus available to plants, insoluble phosphate rock must be treated with an acid to convert it into soluble phosphate salts.

The key raw materials and products in fertiliser production include:

Exam Tip: You need to be able to compare the industrial production of these salts with their laboratory preparation. For example, in the lab, you would make ammonium sulfate by titrating ammonia solution with sulfuric acid. In industry, it’s a large-scale continuous process using raw materials from the Haber process and other sources.