Topic 10: Earth's Resources (1)

What are natural resources

Natural resources form without human input. They include anything that comes from the earth, sea or air. We use them to provide energy for things like warmth, shelter, food and transport

Examples of natural products that are supplemented or replaced by agricultural and synthetic products

• Rubber is extracted from the sap of a tree, however man-made polymers have now been made which can replace rubber in uses such as tyres

• Wood has been replaced by plastics in many applications. For example laminate flooring is composed of a polymer resin and a man-made wood composite. Window frames are now mainly made from a polymer

• Cork is produced from the bark of a tree and can be used as a wine stopper. Synthetic corks, made of plastics, are now used in place of natural cork to prevent tainting of the wine by a chemical found in the bark

What does agriculture provide

Conditions where natural resources can be enhanced for our needs. For example, the development of fertilisers has meant we can produce a high yield of crops

Distinguish between finite and renewable resources

Renewable Resources:

• can be reformed at a similar rate to, or faster than, we use them

Examples:

• timber is a renewable resource, as trees can be planted following a harvest and only take a few years to regrow. Other examples include vegetable crops and sustainably caught fish

Finite (non-renewable) resources:

• can’t be formed quickly enough to be considered replaceable

• after they’ve been extracted, many finite resources undergo man-made processes to provide fuels and materials necessary for modern life

Examples:

• Include fossil fuels and nuclear fuels such as uranium and plutonium

• Minerals and metals found in ores in the earth are also non-renewable materials

What is sustainable development

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

What is potable water

water that’s been treated or is naturally safe for humans to drink - it’s essential for life

Why is potable water not pure

Potable water is not pure water in the chemical sense because pure water only contains H₂O molecules whereas potable water can contain lots of other dissolved substances

What is fresh water

• Fresh water is water that doesn’t have much dissolved in it. For example:

In the United Kingdom, rain provides water with low levels of dissolved substances (freshwater) that can be collected as surface water (lakes, rivers, and reservoirs) or as groundwater (in rocks called aquifers that trap water underground)

What do the methods used to produce potable water depend on

The source of fresh water chosen depends on location. Surface water tends to dry up first, so in warm areas most of the domestic water supply comes from groundwater.

Steps to treat fresh water

1. Filtration - a wire mesh screens out large twigs etc, and then gravel and sand beds filter out any solid bits

2. Sterilisation - the water is sterilised to kill any harmful bacteria or microbes. This can be done by bubbling chlorine gas through it or by using ozone or ultraviolet

What is the definition of:

• Residue

• Filtrate

Residue - an insoluble solid that remains on the filter paper

Filtrate - the solution/water that has been filtered

What happens if supplies of fresh water are limited

If supplies of fresh water are limited, seawater must be treated by desalination to provide potable water. Desalination of seawater can be done by distillation or by processes that use membranes such as reverse osmosis.

These processes require large amounts of energy, so they're really expensive and not used if there are other sources available

What happens during reverse osmosis

Salty water is passed through a membrane that only allows water molecules to pass through. Ions and larger molecules are trapped by the membrane and so separated from the water

Sources of waste water

Urban lifestyles and industrial processes produce large amounts of wastewater that require treatment before being released into the environment

• Sewage and agricultural wastewater require removal of organic matter and harmful microbes

• Industrial wastewater also requires removal of organic matter and harmful chemicals

Stages of wastewater treatment

Screening -

• Before being treated, the sewage is screened - this involves removing any large bits of material (like twigs or plastic bags) and any grit

Sedimentation -

• The screened waste stands in a settlement tank and undergoes sedimentation - the heavier suspended solids sink to the bottom to produce sludge, while the less dense effluent floats on the top

Aerobic digestion -

• The effluent in the settlement tank is removed and treated by biological aerobic digestion. Air is pumped through the water to encourage aerobic bacteria to break down any organic matter

Anaerobic digestion -

• The sludge from the bottom of the settlement tank is also removed and transferred into large tanks. Here, it gets broken down by bacteria in anaerobic digestion. Anaerobic digestion breaks down the organic matter in the sludge, releasing methane gas, which is used as an energy source, and the remaining digested waste can be used as a fertiliser

Advantage and disadvantage of producing potable water from wastewater compared to fresh water and sea water

Advantage - uses less energy than desalination

Disadvantage - requires more processing than treating fresh water so costs more or public may be against drinking recycled water

Is the supply or copper-rich ores limited or unlimited

limited and the demand for copper is growing!

What is the new way of extracting copper

low grade ores - ores that only contain small amounts of copper

What are the two methods used to extract copper from low grade ores

1. Bioleaching

• Uses bacteria which convert copper compounds in the ore into soluble copper compounds, separating out the copper from the ore in the process

2. Phytomining

• The plant absorbing copper through the roots

• The plant being harvested, dried and burned

• The metal compound being collected from the ash

• The metal being obtained from its compound by displacement or electrolysis

Advantages and disadvantages of Bioleaching and phytomining

Advantages:

• Conserves high-grade ores

• Avoids the large amount of digging, moving, and disposing of rock involved in traditional mining

• Conserves energy

• Less pollution

Disadvantages:

• The process is slow

• Sometimes electrolysis is used to purify the extracted metal which uses energy

Name the two methods used to extract copper from the copper compound obtained from phytomining or bioleaching

• Displacement using scrap iron

• Electrolysis

Why are life cycle assessments carried out?

to assess the environmental impact of a product

Name the four main stages of a life cycle assessment.

• Getting the raw materials

• Manufacturing and packaging

• Using the product

• Product disposal

Is it fairly easy to quantify the use of water, resources, energy sources and production of some waste.

yes

It is easy to allocate a numerical value to the polluting effect of a product when carrying out a LCA.

no

Is a life cycle assessment an objective process

no

compare LCAs for shopping bags made from plastic and paper

Plastic Bag:

• Raw materials - crude oil

• Manufacturing and packaging - the compounds needed to make the plastic are extracted from crude oil by fractional distillation, followed by cracking and then polymerisation. Waste is reduced as the other fractions of crude oil have other uses

• Using the product - can be reused. Can be used for other things as well as shopping, eg bin liners

• Product disposal - recyclable but not biodegradable and will take up space in landfill and pollute land

Paper Bag:

• Raw materials - timber

• Manufacturing and packaging - pulped timber is processed using lots of energy. Lots of waste is made

• Using the product - usually only used once

• Product disposal - biodegradable, non-toxic and can be recycled

Conclusion of comparing plastic bag and paper bag

Life cycle assessments have shown even though plastic bags aren’t biodegradable, they take less energy to make and have a longer lifespan than paper bags, so they may be less harmful to the environment

What are reuse and recycling

• Reusing a product can mean using it more than once for the same purpose or putting a used product to a new purpose

• Recycling involves using waste materials to make new products

Why do materials such as glass and metal need to be recycled and reused?

Because they are made from natural but finite sources

Advantages and disadvantages of recycling metals

Advantages:

• Reduces energy use

• Conserves raw materials

• Reduces the amount of waste sent to landfill

Disadvantages:

• Materials need to be collected and transported which requires energy and fuel

• Workers, vehicles, and worksites need to be organised and maintained

• Materials need to be sorted before they can be recycled

• Products made from recycled materials may not always be of the same quality

How does recycling impact the use of fossil fuels

reduces the use of fossil fuels

Describe the process of recycling metals

Metals can be recycled by heating the metal until it melts and recasting them into a new shape

Describe how a glass bottle can be recycled

A glass bottle can be recycle by being crushed and melted, and then remoulded into a different shape

what is much more energy efficient, to recycle metals or to extract them as melting and re-moulding

recyle metals

what determines the amount of separation required for recycling

• The material being recycled

• The properties required of the final product

Where does most of the energy needed to produce raw materials, such as glass, come from

Limited resources

How is glass separated before being recycled

by colour and chemical composition

What is corrosion

Corrosion is when a metal is gradually destroyed by reacting with substances in the environment. An example is when iron rusts

What is necessary for iron to rust

iron needs to be in contact with both oxygen and water, which are found in the air, to form hydrated iron oxide - which we call rust

Word equation for rusting of iron

What protects aluminium from further corrosion

Aluminium has an oxide coating that protects the metal from further corrosion

How to show that both oxygen and water are required for rust to form

• if you put an iron nail in boiling tube with just water, it won’t rust (the water is boiled to remove oxygen and oil is used to stop air getting in)

• if you put an iron nail in a boiling tube with just air, it won’t rust (calcium chloride can be used to absorb any water from the air)

• however if you put an iron nail in a boiling tube with air and water, it will rust. The mass of a rusty nail will increase as the iron atoms in the nail have now bonded to oxygen and water molecules, resulting in a compound that is heavier than iron alone

Preventing corrosion

• Painting metals - creates a barrier which prevent oxygen from reaching the metal

• Oiling and greasing metals - prevents water from reaching the metal

• Galvanizing - iron is coated with a thin layer of zinc, which prevents both water and oxygen from reaching them metal and zinc also acts as a sacrificial metal

What is meant by sacrificial protection?

Sacrificial protection is when a more reactive metal is intentionally allowed to corrode to protect the metal it is covering

What is the sacrificial method

involves placing a more reactive metal with the metal you want to protect. Water and oxygen then react with the sacrificial metal instead of with the less reactive metal

Exam Q: Describe how iron is a typical transition metal, referring to its properties, including density, melting point, and catalytic activity

A transition metal is an element which forms one or more stable ions (1)

High melting point (1)

High density (1)

Forms coloured compounds (1)

Often used as catalysts as they speed up reactions (1)

Iron is used in the Haber Process (1)

Exam Q: A statue has been built out of iron. Explain how the statue could be prevented from rusting, referring to at least two different methods.

Metals corrode due to oxidation (1)

Both water and oxygen are required for rusting to occur (1)

Exclusion of Oxygen (1)

Paint can be used as a barrier to prevent oxygen from reaching the metal (1)

Exclusion of Water (1)

Water repellent oil or grease layer to prevent water from reaching the metal (1)

Sacrificial Protection (1)

Using a more reactant metal that will be preferentially oxidised, for example aluminium. This metal corrodes, but the iron doesn’t (1)

Iron can be coated with a thin zinc layer, this is known as galvanising (1)

What is an alloy

Alloys are mixtures of two or more metals, or a mixture of a metal and a non-metal

• Most metals in use today are actually alloys

Why are pure metals often unsuitable for some uses

Pure copper, gold, iron, and aluminium are all too soft for everyday uses because their layers of atoms slide over each other and so are mixed with small amounts of similar metals to make them harder for everyday use

Why are alloys harder than pure metals

alloys are harder than pure iron because the atoms are different sizes which distort the regular arrangements of atoms, preventing the layers from sliding over each other easily

What are the advantages of using alloys over pure metals?

• Greater strength

• Greater hardness

• Increased resistance to corrosion

• Increased resistance to extreme temperatures

How is steel formed

by adding small amounts of carbon, and sometimes other metals, to the iron

What are the different types of steel and what are their properties and uses

Low-carbon steel:

• Properties - easily shaped

• Uses - car bodies

High carbon steel:

• Properties - very strong, inflexible, brittle

• Uses - blades for cutting tools, bridges

Stainless steel:

• Properties - corrosion-resistant, hard

• Uses - cutlery, containers for corrosive substances

Common alloys

Bronze:

• an alloy of copper and tin

• good for making statues, decorative objects and medals

Brass:

• an alloy of copper and zinc

• used in water taps and door fittings

Gold:

• an alloy of zinc, copper, and silver

• used to make jewellery

• the amount of gold in a gold alloy in measured in carats

• 24 carat = 100% (pure gold), and 18 carat = 75% gold

Aluminium:

• low density

• used for aircraft

What are ceramics

• non-metallic solids with high melting points that aren’t made from carbon-based compounds

• excellent insulators of heat and electricity

• very brittle (not very flexible and break easily) and also stiff

how is clay ceramics formed

Clay is a soft material when it is dug up out of the ground, so it can be moulded into different shapes. When it’s fired at high temperatures, it hardens to form a clay ceramic

Why is clay ideal for making pottery and bricks

clay can be moulded when wet and then be hardened

Glass properties

• transparent

• can be moulded when hot

• can be brittle (not very flexible and break easily) when thin

Different types of glass

Soda lime glass:

• Most glass is soda lime glass, which is made by heating a mixture of limestone, sand, and sodium carbonate (soda) until it melts

• When the mixture cools, it comes out as glass

Borosilicate glass:

• Has a higher melting point than soda lime glass

• It’s made in the same way as soda lime glass, using a mixture of sand and boron trioxide

What are composites made off

One material embedded in another → fibres or fragments of a material (known as the reinforcement) are surrounded by a matrix acting as a binder

What do the properties of composites depend on

the matrix/binder of the reinforcement used to make them, so they have many different uses

Examples of composites

Wood:

Matrix - lignin, an organic polymer

Reinforcement - cellulose fibres

Properties - versatile, strong, attractive appearance

Uses - gives trees strength, a building material

Fibreglass:

Matrix - polymer resin (plastic)

Reinforcement - thin glass fibres

Properties - low density, very strong

Uses - skis, boats, and surfboards

Carbon fibre:

Matrix - a polymer resin

Reinforcement - carbon fibres or carbon nanotubes

Properties - very strong, light

Uses - in aerospace and sports car manufacturing

Concrete:

Matrix - cement

Reinforcement - sand and gravel (aggregate)

Properties - strong and rigid

Uses - a building material eg in skate parks

Metals properties

• malleable

• good conductors of heat and electricity

• ductile (can be drawn into wires)

• shiny

• stiff