C.12

Question 1

Why are humans dependant on natural resources?

Answer 1

Humans need natural “raw” resources for food, warmth, shelter and transport

Question 2

How is modern agriculture used to obtain natural resources?

Answer 2

Many resources are obtained by agriculture, and modern agriculture helps us meet global demands. Furthermore, the use of biofuels allows us to farm natural resources more efficiently and sustainably.

Question 3

What are synthetic materials?

Answer 3

Synthetic materials are materials made by chemists to replace natural resources
- e.g. rubber made from crude oil to replace natural rubber obtained from sap

Question 4

Define finite resources

Answer 4

Finite resources are resources which are non-renewable and will eventually run out if they continue to be used at the current rate.

Question 5

Define sustainability

Answer 5

Meeting the needs for the current generations without compromising the needs of future generations

Question 6

What is the difference between pure and potable water?

Answer 6

Pure water is water containing the compound water only and contains no dissolved substances. It has a pH of 7. Potable water is water which is safe to drink, however, it does contain dissolved substances and may not have a pH of 7.

Question 7

Explain how to identify pure water by crystallisation?

Answer 7

1. Take a sample of water and place it onto Universal Indicator paper. If the paper turns green, the pH of the water is 7 and the water is pure. If the paper does not turn green however, the water contains dissolved acidic or alkaline substances.
2. Use a balance to measure the mass of an evaporating basin, then fill it with the water sample and gently heat until all of the water has evaporated.
3. Measure the mass of the basin again. If it has increased, then there will be crystallised solids in the basin and therefore the water was definitely impure.
4. If the mass does not increase however, the water may still have been pure, even though it may contain dissolved gases.

Question 8

Explain how to identify pure water by distillation.

Answer 8

1. Set up a conical flask containing the water sample over a tripod and bunsen burner, and use a delivery tube to connect the flask to a test tube sitting in a beaker of ice and water.
2. Gently heat the water until it boils slightly. The water will evaporate and the vapour should pass through the delivery tube and condense in the test tube as distilled water.

Question 9

How is potable water obtained from freshwater or groundwater?

Answer 9

Water is taken from rivers, lakes, reservoirs or aquifers and passed through filter beds which removes any leaves or suspended particles. It is then sterilised using chlorine, ozone or UV light to kill any microbes or bacteria.

Question 10

How is potable water obtained from salt water?

Answer 10

This process is known as desalination. It can either be done by distillation or by reverse osmosis, which is where water is passed through membranes. However, both of these methods are expensive as they require a large amount of energy.

Question 11

Explain how waste water is managed.

Answer 11

1. Sewage water is screened by passing through a mesh which removes any pieces of grit or solids.
2. The sewage then settles in a large sedimentation tank. This produces a liquid effluent and a semi solid sludge, from which the sludge is removed and digested by anaerobic bacteria which produces biogas. This biogas can be burned to produce electricity, and the digested sludge can be used as farming fertilisers.
3. Air is bubbled through the liquid effluent, allowing aerobic bacteria to multiply and digest any organice molecules or harmful microorganisms in the presence of oxygen.
4. The liquid effluent is now safe to return to a river.

Question 12

What is the best way to obtain potable water?

Answer 12

Using unpolluted aquifers is the easiest way to obtain potable water, as using saltwater is very expensive, and waste water has many steps to achieve purification. Both of these methods require a lot of energy.

Question 13

What is the problems with metal extraction and what are the solutions?

Answer 13

Demand for metals such as copper is increasing but copper sources are scarce. This forces us to use low grade ores which is not economically viable.
This issue is usually solved by using either phytomining or bioleaching.

Question 14

Explain how phytomining works.

Answer 14

1. Plants are grown on land containing the desired metal compound. The plants then absorb the compound and concentrate it in their tissue.
2. The plants are harvested and burnt, and the ash produced contains a high concentration of the desired metal compound.
3. The metal must now be extracted from it’s compound by electrolysis or using a displacement reaction - it is easy to extract copper, as scrap iron can be used to displace it which is very cheap.

Question 15

Explain how bioleaching works.

Answer 15

1. Bacteria is mixed with the low grade ore. It carries out chemical reactions and produces a solution known as a leachate which contains the desired metal compound.
2. The metal must now be extracted from it’s compound by electrolysis or using a displacement reaction - it is easy to extract copper, as scrap iron can be used to displace it which is very cheap.

Question 16

Why is bioleaching and phytomining good?

Answer 16

They are great as they allow us to economically obtain metal from low grade ores. They also do not involve digging, transporting and disposing of large amounts of rock unlike mining and quarrying methods.

Question 17

Why is quarrying and mining bad for the environment?

Answer 17

Both methods require a large amount of energy. Quarrying releases dust into the air and it damages the environment. Mining also releases harmful chemicals.

Question 18

How can products be reused?

Answer 18

Products such as glass bottles can be reused easily, or they can be crushed and melted to form new glass products such as jars.

Question 19

How can products be recycled?

Answer 19

Products such as plastic bottles can be recycled and made into different products. Metal products however, must be melted and recasted to create new products. Sometimes this required the seperation of metals. Both reusing and recycling products reduces are reliance on the Earth’s raw materials.

Question 20

What is a life cycle assessment?

Answer 20

An assessment of the life of a product which attempts to put a number on it’s environmental impacts. It assesses the extracting and processing of the raw materials, the lifetime of the product, and the end of the product’s life.

Question 21

Describe the first stage of a life cycle assessment.

Answer 21

Extracting and processing of raw materials:

Polymers/plastics - crude oil extracted -> transported -> seperated -> cracked -> polymer produced
Metals - ore dug out -> transported -> extracted -> often produces toxic waste products

All of these stages require a lot of energy and usually, the burning of fossil fuels. All products then must be manufactured, packaged and transported.

Question 22

Describe the second stage of a life cycle assessment.

Answer 22

During the lifetime of the product

For example, a product may use batteries throughout it’s life time which produces toxic waste.

Question 23

Describe the third stage of a life cycle assessment.

Answer 23

End of life - harmful chemicals must be disposed of carefully and safely and products must be transported for disposal. Both of these processes require a lot of energy.

Question 24

What are the issues of LCAs?

Answer 24

• They can be biased and often use subjective data
• Uncertainty over the environmental damage caused means LCAs often use estimates or value judgements.

Question 25

Form an LCA comparing a plastic and paper bag.

Answer 25

• Paper bag made from wood which is renewable, plastic from crude oil which is non-renewable
• Both can harm the environment - crude oil in the case of an oil spill, and wood as felling trees destroys habitats.
• Both need processing which uses energy and often the combustion of fossil fuels.
• Plastic bags can often be reused but paper bags often cannot.
• Both need transporting, as paper bags are heavier they will require more energy.
• Plastic is both non-biodegradable and non recyclable, meaning it will not naturally decompose.

Question 26

How do we use copper sulfate to test for water?

Answer 26

Pure copper sulfate is white and it is known as anhydrous copper sulfate because it has no water in it. However, if the copper sulfate turns blue then it is in the presence of water or water vapour.

anhydrous copper sulfate + water –> hydrated copper sulfate
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