Using the Earth's resources and obtaining potable water

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レッスンノート

Using the Earth's Resources

Humans use the Earth's resources to provide warmth, shelter, food and transport.
Natural resources can be living (plants and animals) or non-living (minerals, fossil fuels, water and air).
Some natural products can be replaced by synthetic products, e.g. rubber from tree sap (latex) can be replaced by polymers.
Agriculture supplements natural resources, e.g. fertilisers are used to enhance crop yield.
Chemistry plays an important role in improving agricultural and industrial processes to provide new products and in sustainable development.

Finite and Renewable Resources

Renewable resources can be replenished or replaced within a human timescale, e.g. timber from trees that can be replanted.
Finite (non-renewable) resources do not reform quickly enough or do not reform at all, e.g. minerals from the Earth's crust and metal ores.
Crude oil is a finite resource because it takes millions of years to form.
Extracting and processing non-renewable resources requires energy and makes the process less sustainable.
Recycling and re-using materials reduce the need to exploit finite mineral resources.

Finite and renewable resources

Sustainable Development

Sustainable development meets the needs of current generations without compromising the ability of future generations to meet their own needs.
Chemists design processes and materials to be more sustainable, e.g. developing polymers to replace natural rubber.
Using recycled aluminium is more sustainable than extracting aluminium from its ore because it saves energy and conserves finite resources.
Fertilisers are an example of scientific advancement maximising the production of natural products.

Potable Water

Potable water is water that is safe for human consumption; it is not pure water in the chemical sense because it contains dissolved substances.
Pure water is made up solely of H₂O molecules, whereas potable water contains dissolved minerals and salts in small regulated quantities.
Potable water should have a pH between 6.5 and 8.5, very low levels of dissolved salts, and be free of bacteria and harmful microbes.
Fresh water is relatively free from dissolved substances, e.g. rainwater; it collects in reservoirs, lakes and rivers (surface water) or in aquifers (groundwater).
In the UK, most potable water is produced by choosing an appropriate fresh water source, passing it through filter beds, and sterilising it.
Sterilising agents include chlorine, ozone or ultraviolet light.

Treating fresh water to make it potable

Desalination

Desalination is the treatment of seawater to remove salt, used when fresh water supplies are limited.
Desalination can be done by distillation or by processes using membranes such as reverse osmosis.
In reverse osmosis, salt water is forced through a semi-permeable membrane that allows only water molecules to pass, stopping larger molecules and ions.
Desalination is expensive because it requires large amounts of energy.
It is used in regions with very hot climates and scarce rainfall, such as Saudi Arabia and parts of the Middle East.

Desalination by distillation and reverse osmosis

Required Practical: Analysis and Purification of Water Samples

Analysing water samples: measure pH (using a pH meter or universal indicator) and the mass of dissolved solids.
To find dissolved solids: weigh an empty evaporating basin, add a measured volume of water, heat gently until most water evaporates, leave to fully evaporate, then reweigh.
The mass of dissolved solids = (mass of basin + solids) − (mass of empty basin).
Purification by distillation: set up simple distillation apparatus, heat the water sample until boiling, collect the distilled water in a cooled test tube.
The delivery tube must sit above the filtrate level to prevent cold water being sucked back and breaking the hot glass.
The distillate is pure water; its purity can be checked by determining its boiling point.

Analysing and distilling a water sample

Waste Water Treatment

Domestic and agricultural waste water require removal of organic matter and harmful microbes.
Industrial waste water may require removal of organic matter and harmful chemicals.
Sewage treatment stages: screening and grit removal → sedimentation → anaerobic digestion of sludge → aerobic biological treatment of effluent.
Sedimentation produces sewage sludge (heavier solids sink) and effluent (lighter matter floats).
Anaerobic digestion breaks down sewage sludge and releases methane gas, which can be used as an energy source; leftover digested waste can be used as fertiliser.
Aerobic digestion pumps air into the effluent to encourage aerobic bacteria to break down organic matter and microbes.
Additional treatment for toxic substances may include membranes, adding chemicals to precipitate metals, and UV radiation.

Waste water treatment stages

Alternative Methods of Extracting Metals

Low-grade ores contain very low percentages of metal compounds; traditional mining is only economically viable for high-grade ores.
Phytomining uses plants to absorb metal compounds through their roots; the plants are harvested, dried and burned to produce ash containing metal compounds.
Bioleaching uses bacteria to produce leachate solutions containing metal ions, e.g. copper(II) ions.
The metal compounds from phytomining and bioleaching can be processed to obtain the metal by displacement using scrap iron or by electrolysis.
These biological methods avoid the digging, moving and disposing of large amounts of rock associated with traditional mining.
Disadvantages: biological methods are very slow and bioleaching produces toxic substances that need treatment.
Phytomining and bioleaching are mainly used for copper extraction because copper ores are becoming scarce, but can be applied to other metals.

Alternative methods of extracting metals

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練習問題

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1.Which of the following is NOT obtained from the Earth's resources?
Easy
- AShelter
- BSunlight
- CWarmth
- DFood
2.Which of the following is an example of a synthetic product?
Easy
- AWood
- BRubber
- CPoly(ethene)
- DCeramics
3.Which of these natural resources is finite?
Easy
- AWood
- BCereal grains
- CCrude oil
- DTimber
4.What does potable water mean?
Easy
- AWater that is safe to drink
- BWater that is chemically pure
- CWater that contains no dissolved substances
- DWater that has been distilled
5.Which of the following could NOT be used to sterilise water?
Easy
- AFluoride
- BChlorine
- COzone
- DUltraviolet light
6.Which of the following is the incorrect reason for the water treatment step being carried out?
Easy
- AFiltration to remove dissolved solids
- BDesalination to remove salt
- CReverse osmosis to remove salt
- DSterilisation to kill bacteria
7.What is meant by the term 'low-grade ores'?
Medium
- AThe copper produced from these ores does not have a high economical value
- BThey contain very low percentages of copper compounds
- CThe copper they contain is impure
- DThey are found deep underground
8.Match each method of extraction to the substance that is used to extract copper.
Medium
- Phytomining
- Bioleaching
- Plants
- Bacteria

もっと問題

9.What is the reason for carefully monitoring the amount of chlorine used in swimming pools?
Easy
- AIt is flammable
- BIt is corrosive
- CIt is toxic
- DIt is a diuretic
10.Which two substances need to be removed from sewage and agricultural waste water? (select all that apply)
Medium
- AFluoride
- BHarmful microbes
- CDissolved salts
- DOrganic matter
11.Which two substances need to be removed from industrial waste water? (select all that apply)
Medium
- AHarmful chemicals
- BHarmful microbes
- CSodium ions
- DOrganic matter
12.Which of the following is NOT a characteristic of potable water?
Easy
- AIt has a pH between 6.5 and 8.5
- BIt contains no dissolved substances at all
- CIt is free of bacteria or harmful microbes
- DIt contains dissolved substances in very small regulated quantities
13.Potable water is pure water in the chemical sense.
Easy
True or false?
14.Desalination is a cheap and low-energy process.
Easy
True or false?
15.Filtration is used to sterilise water.
Easy
True or false?
16.Renewable resources are the same as sustainable resources.
Easy
True or false?
17.Match each method of extracting copper from low-grade ores to the substance that carries out the extraction.
Medium
- Phytomining
- Bioleaching
- Plants
- Bacteria
18.Place the stages of sewage treatment into the correct order, from first to last.
Medium
- Screening and grit removal
- Sedimentation
- Anaerobic digestion of sewage sludge
- Aerobic biological treatment of effluent
19.Which of the following are used as sterilising agents when producing potable water? (select all that apply)
Medium
- AChlorine
- BOzone
- CUltraviolet light
- DSand
- EGravel
20.Which of the following statements about potable water are correct? (select all that apply)
Medium
- AIt is safe for human consumption.
- BIt is pure water in the chemical sense.
- CIt may contain dissolved minerals and salts.
- DIt must be free of bacteria and harmful microbes.
- EIt has a pH between 6.5 and 8.5.
21.Which of the following are reasons why desalination is expensive? (select all that apply)
Medium
- AIt requires large amounts of energy.
- BIt uses distillation which involves heating water.
- CIt can only be done in cold climates.
- DIt produces large volumes of waste water.
- EIt requires expensive membranes for reverse osmosis.
22.Match each water sample to its most likely source, using the pH and dissolved solids data.
Medium
- Sample A: pH 8.2, 0.72 g dissolved solids
- Sample B: pH 4.2, 0.03 g dissolved solids
- Sample C: pH 7.0, 0.00 g dissolved solids
- Sea water
- Acid rain
- Pure water
23.Which of the following are advantages of using phytomining and bioleaching compared with traditional mining? (select all that apply)
Medium
- AThey avoid digging, moving and disposing of large amounts of rock.
- BThey can extract metals from low-grade ores.
- CThey are faster than traditional mining.
- DThey can be used to clean up mining waste.
- EThey do not require any further processing to obtain pure metal.
24.Which of the following statements about the ease of obtaining potable water from different sources are correct? (select all that apply)
Hard
- AGround water may need very little treatment to make it potable.
- BSalt water requires desalination, which is energy-intensive.
- CWaste water treatment is shorter than treating fresh water.
- DGround water can contain natural minerals such as arsenic that make it unsafe.
- EBoiling ground water will remove dissolved minerals.
25.A water sample has a pH of 5.8 and contains 0.09 g of dissolved solids per 25 cm³. Which type of water is it most likely to be?
Medium
- AFresh water from a river
- BSea water
- CPure distilled water
- DRainwater collected in a clean container
26.A student evaporated 20 cm³ of a water sample to dryness and found 0.04 g of dissolved solids. What mass of dissolved solids would be present in 1 dm³ of the same water?
Medium
- A0.20 g
- B2.00 g
- C0.80 g
- D8.00 g
27.A sample of sea water is desalinated by distillation. Which statement explains why this process is expensive?
Medium
- AIt requires a lot of energy to heat the water.
- BIt requires expensive membranes that need frequent replacement.
- CIt produces large amounts of sewage sludge that must be treated.
- DIt needs chlorine gas to be bubbled through the water.
28.Which of the following is the correct order of stages in sewage treatment?
Medium
- AScreening and grit removal → sedimentation → aerobic digestion of effluent → anaerobic digestion of sludge
- BSedimentation → screening and grit removal → anaerobic digestion of sludge → aerobic digestion of effluent
- CScreening and grit removal → anaerobic digestion of sludge → sedimentation → aerobic digestion of effluent
- DAerobic digestion of effluent → sedimentation → screening and grit removal → anaerobic digestion of sludge
29.A sample of ground water contains dissolved arsenic minerals. Which treatment would make it safe to drink?
Hard
- ABoiling the water
- BPassing it through a charcoal filter
- CAdding chlorine gas
- DFiltering through sand beds
30.A student sets up simple distillation to purify a water sample. Why must the delivery tube sit above the level of the liquid in the collection tube?
Medium
- ATo allow the water vapour to escape
- BTo prevent cold water being sucked back up the delivery tube and cracking the hot glass
- CTo increase the rate of distillation
- DTo stop the water from boiling too quickly
31.Which of the following statements about obtaining potable water from different sources are correct? (select all that apply)
Medium
- AGround water may need very little treatment to make it potable.
- BDesalination is used in areas with very little rainfall or ground water.
- CWaste water treatment uses less energy than desalination of salt water.
- DSalt water is easier to treat than ground water.
- ESewage treatment is quicker than treating fresh water.
32.Which of the following are products of anaerobic digestion of sewage sludge? (select all that apply)
Medium
- AMethane gas
- BDigested waste used as fertiliser
- CEffluent
- DSewage sludge
- ECarbon dioxide
33.Potable water must have a pH between 6.5 and 8.5.
Easy
True or false?
34.Boiling ground water will remove dissolved arsenic minerals.
Easy
True or false?
35.Match each water source to the most appropriate treatment method.
Medium
- Ground water containing arsenic
- Sea water
- Fresh water from a river
- Sewage sludge
- Charcoal filtration
- Distillation or reverse osmosis
- Filtration and sterilisation
- Anaerobic digestion
36.Place the stages of treating fresh water to make it potable into the correct order, from first to last.
Medium
- Sedimentation
- Filtration
- Sterilisation
37.Which sample is most likely to be sea water?
Medium
- ASample A
- BSample B
- CSample C
- DSample D
38.Which sample is most likely to be pure distilled water?
Medium
- ASample C
- BSample B
- CSample D
- DSample A
39.A company extracts copper from a low-grade ore using bioleaching. Which statement about this method is correct?
Hard
- AIt uses plants to absorb copper compounds.
- BIt produces a leachate solution containing copper ions.
- CIt requires high temperatures to melt the ore.
- DIt is faster than traditional mining.
40.Which of the following are disadvantages of using phytomining and bioleaching to extract copper? (select all that apply)
Hard
- AThey are very slow processes.
- BThey require displacement or electrolysis to obtain pure copper.
- CThey cause significant environmental damage from digging.
- DThey can only be used for copper.
- EThey produce toxic substances that need treatment.
41.Complete the sentence about sustainable development using the words from the box: current, previous, compromising, future, allowing.
Easy
Sustainable development meets the needs of ____ generations without ____ the ability of ____ generations to meet their own needs.
42.What is the name of the process used in the first stage of water treatment to remove solid particles such as soil, twigs and small pebbles?
Easy
43.Complete the sentences about phytomining and bioleaching using the words from the box: ash, leachate, electrolysis.
Medium
Phytomining results in the production of ____ that contains metal compounds. Bioleaching produces ____ solutions that contain metal compounds. The metal compounds produced can be processed further to obtain the metal, for example, copper can be extracted from copper compounds by displacement by scrap iron or ____.
44.Name the three stages of treating fresh water to make it potable.
Easy
The three stages are ____, ____, and ____.
45.Name the process used in the first stage of water treatment to remove solid particles such as soil, twigs and small pebbles.
Easy
46.A 20 cm³ sample of water contains 0.03 g of dissolved solids. What mass of dissolved solids would be present in a 100 cm³ sample of the same water?
Medium
47.Complete the sentences about the treatment of waste water.
Medium
In sedimentation, heavier solids sink to form sewage ____, while lighter matter floats to form ____. The sludge is then broken down by ____ digestion, which releases methane gas.
48.A 25 cm³ sample of water contains 0.05 g of dissolved solids. What mass of dissolved solids is present in 100 cm³ of the same water? Give your answer in grams.
Medium
49.Complete the sentence about obtaining potable water from salt water.
Medium
Desalination can be done by distillation or by reverse ____.
50.Name the process used to remove large materials such as plastic bags and twigs from sewage.
Easy
51.What mass of dissolved solids would be present in 100 cm³ of sample B? Give your answer in grams.
Medium
52.Explain why potable water is not chemically pure.
Hard
53.Describe how waste water is treated to make it safe for release into the environment.
Hard
54.Explain why potable water is not pure water in the chemical sense.
Hard
55.A 20 cm³ sample of water contains 0.03 g of dissolved solids. What mass of dissolved solids would be present in a 100 cm³ sample of the same water?
Medium
- A1.15 g
- B2.15 g
- C-0.85 g
- D0.15 g
56.A 25 cm³ sample of water contains 0.05 g of dissolved solids. What mass of dissolved solids is present in 100 cm³ of the same water? Give your answer in grams.
Medium
- A0.2 g
- B1.2 g
- C2.2 g
- D-0.8 g
57.What mass of dissolved solids would be present in 100 cm³ of sample B? Give your answer in grams.
Medium
- A-0.85 g
- B2.15 g
- C0.15 g
- D1.15 g

フラッシュカード

What is potable water?

Water that has been processed and is safe for humans to drink and use. It has sufficiently low levels of dissolved salts and microbes.

Why is potable water not pure water in the chemical sense?

Pure water is made up solely of H₂O molecules, whereas potable water also contains dissolved substances such as minerals and salts.

State three characteristics of potable water.

It has a pH between 6.5 and 8.5, dissolved substances are present in very small regulated quantities, and it is free of bacteria and harmful microbes.

What is meant by fresh water?

Water that is relatively free from dissolved substances, such as rainwater.

What is surface water and where is it found?

Fresh water that collects in reservoirs, lakes and rivers.

What is groundwater and where is it stored?

Water that collects underground in aquifers, which are porous rocks that store water.

Describe the two main steps used to treat fresh water to make it potable.

Filtration removes debris such as soil, pebbles and twigs (through a wire mesh screen, then sand beds and gravel); sterilisation kills dangerous bacteria and microbes.

Name three sterilising agents used to make potable water.

Chlorine (bubbled through as a gas), ozone, and ultraviolet light.

What is desalination?

The treatment of salty water or sea water to remove the salt so it can be made potable.

State two methods used to desalinate sea water.

Distillation and reverse osmosis (using membranes).

Why is desalination an expensive process?

It requires large amounts of energy, so it is only used when there is no alternative supply of fresh water.

How does reverse osmosis remove salt from water?

Salt water is forced through a semi-permeable membrane that only allows small water molecules to pass through, stopping larger molecules and ions.

Which two substances must be removed from sewage and agricultural waste water?

Organic matter and harmful microbes.

Which two substances may need to be removed from industrial waste water?

Harmful chemicals and organic matter.

Name the stages of sewage treatment in order.

Screening and grit removal, sedimentation, anaerobic digestion of sewage sludge, and aerobic biological treatment of effluent.

What happens during sedimentation in sewage treatment?

Water stands still in a settlement tank; heavier solids sink to form sewage sludge while lighter matter (effluent) floats to the top.

What is produced by the anaerobic digestion of sewage sludge?

Methane gas, which is used as a source of energy, and leftover digested waste used as a fertiliser.

What happens during the aerobic biological treatment of effluent?

Air is pumped into the water to encourage aerobic bacteria to break down organic matter and microbes.

How can toxic substances be removed from waste water?

Using membranes, adding chemicals (e.g. to precipitate metals out of solution), and U.V. radiation.

Why is treating waste water often preferred to desalination where fresh water is scarce?

It takes longer than treating fresh water, but it uses less energy than desalinating salt water.

What are low-grade ores?

Ores that contain very low percentages of the useful metal compounds.

What is phytomining?

Plants absorb metal compounds through their roots; the plants are harvested and burned to produce ash containing metal compounds.

What is bioleaching?

Bacteria break down ores to form acidic leachate solutions containing metal ions, such as copper(II) ions.

How is copper obtained from the solutions produced by phytomining and bioleaching?

By displacement using scrap iron, or by electrolysis.

Give one disadvantage of traditional mining.

It involves large amounts of digging, moving and disposing of rock, causing significant environmental damage.

Give one disadvantage of phytomining and bioleaching.

They are very slow, and the extracted metal still requires displacement or electrolysis to purify it.

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 the difference between a finite and a renewable resource?

Finite (non-renewable) resources do not reform quickly enough or at all; renewable resources can be replenished within a human timescale.

Give an example of a natural product replaced by a synthetic one.

Rubber (latex from tree sap) can be replaced by polymers developed for the same products.

How can the mass of dissolved solids in a water sample be found?

Weigh an empty evaporating basin, evaporate the water sample in it, then reweigh; the increase in mass is the mass of dissolved solids.

Why is a pH meter preferred over universal indicator for testing water?

It gives a more accurate and precise measurement of pH.

Why is distillation used to purify a water sample in the required practical?

It separates pure clean water from a sample containing water and other substances, and the distillate can be checked by boiling point.

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