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Chemistry A Modern View Exercise Book 3 Suggested answers Contents PART VIII
FOSSIL FUELS AND CARBON COMPOUNDS
Chapter 30 Chapter 31
Chapter 35
Fossil fuels 2 Homologous series, structural formulae and naming of carbon compounds 4 Alkanes and alkenes 6 Consequences of using fossil fuels (Part One): Burning of fuels 8 Consequences of using fossil fuels (Part Two): Environmental problems associated with the use of fossil fuels 9 Alcohols 14
PART XI
PLASTICS AND DETERGENTS
Chapter 36 Chapter 37
Plastics Detergents
PART X
DETECTION AND ANALYSIS
Chapter 38 Chapter 39
Separation of mixtures Detection of substances
Chapter 32 Chapter 33 Chapter 34
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16 21
23 24
-1-
CHAPTER 30 Fossil fuels 1.
B
2.
D
3.
B
4.
A
5.
A
6.
C
7.
B
8.
C
9.
A
10.
D
11.
(a)
It is a complex mixture of alkanes. Some of the higher alkanes dissolve in liquid oil to form a solution; besides, the various compounds present lower the melting points of each other.
(b)
Fractional distillation
(c)
1
(d)
1 (refinery gas); 2 (petrol; naphtha); 3 (kerosene); 4 (gas oil)
(e)
Most of the residue is burnt directly as fuel oil in large furnaces such as those in power stations or big ships. A small proportion of it is vacuum distilled to give lubricating oils, waxes and bitumen (for surfacing roads).
(f)
Fraction 2; petrol as motor car fuel, naphtha to produce town gas and alkenes (for preparing many useful chemicals)
(g)
It is immiscible with water and has a density less than 1 g cm−3, hence it forms a layer on the surface of water, suffocating the larvae. Fraction 2 would not be suitable, as it is volatile and will easily evaporate away.
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12.
(a)
Boiling point in °C Percentage (by mass) of crude oil which boils off
below 40
40 − 170
170 − 250
250 − 350
above 350
2
35
11
30
22
(b)
Percentage (by mass) of crude oil which boils off crude oil which boils off
35 30 25 20 15 10 5 0
below 40
40 − 170
170 − 250 250 − 350 above 350 Boiling point (°C)
(c)
40 − 170°C
(d)
North Sea oil
(e)
Yes. North Sea oil contains a higher percentage of the 40 − 170°C fraction (the most valuable fraction).
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CHAPTER 31
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Homologous series, structural formulae and naming of carbon compounds 1.
C
2.
D
3.
A
4.
B
5.
B
6.
C
7.
A
8.
B
9.
A
10.
D
11.
D
12.
B
13.
B
14.
D
15.
(a)
C, D, E
(b)
C, D
(c)
E
(d)
A, B
(e)
A, C, E
(f)
B, D
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16.
(a)
(b)
(c)
(d)
(e)
(f)
17.
A and F
18.
(a)
Pentane
(b)
1-chloro-2-methylbutane
(c)
1-bromo-2,2-dimethylpropane
(d)
1,1,2,3-tetrachloro-2-methylpropane
(e)
Propene
(f)
But-1-ene
(g)
3,3,3-trichloropropene
(h)
3-chlorobutan-1-ol
(i)
2-chloropropanoic acid
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CHAPTER 32
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Alkanes and alkenes 1.
D
2.
B
3.
D
4.
A
5.
C
6.
A
7.
B
8.
C
9.
A
10.
B
11.
B
12.
(a)
A substitution reaction is a chemical change in which an atom (or a group of atoms) of an organic molecule is replaced by another atom (or group of atoms).
(b)
CH4 + Cl2 CH3Cl + Cl2
CH2Cl2 + HCl
CH2Cl2 + Cl2
CHCl3 + HCl
CHCl3 + Cl2 13.
CH3Cl + HCl
CCl4 + HCl
Both are a family of substances, which show gradation in physical properties and similarity in chemical properties.
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14.
(a)
Breaking large organic molecules into smaller ones by heating in the absence of air.
(b)
C5 − C10 alkanes
(c)
CH3(CH2)4CH3
CH3CH2CH2CH3 + CH2=CH2;
CH3(CH2)4CH3
CH3CH2CH3 + CH3CH=CH2 (Other answers may be given.)
(d)
To produce alkenes which serve as starting materials for preparing a great variety of organic compounds.
15.
(e)
To produce extra petrol.
(a)
(i)
Carbon dioxide (CO2), water
(ii)
Toxic gas, carbon monoxide, will be produced in incomplete combustion when there is not enough oxygen.
(b)
16.
(i)
Cracking
(ii)
Useful substances such as petrol and alkenes can be obtained.
(a)
Alkene
(b)
(i)
CH2 = CH2 + Cl2
CH2ClCH2Cl
(ii)
17.
18.
(c)
Ethene can decolorize an acidified solution of potassium permanganate, while hexane cannot.
(a)
Cracking
(b)
Heavy oil fractions such as fuel oil or larger alkanes
(a)
Molecular formula: C3H6
(b)
1,2-dibromopropane
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CHAPTER 33
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Consequences of using fossil fuels (Part One): Burning of fuels
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1.
D
2.
A
3.
D
4.
B
5.
C
6.
B
7.
D
8.
B
9.
C
10.
(i)
(a), (b), (c)
(ii)
(a), (f)
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CHAPTER 34
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Consequences of using fossil fuels (Part Two): Environmental problems associated with the use of fossil fuels
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1.
A
2.
B
3.
B
4.
D
5.
D
6.
B
7.
A
8.
D
9.
C
10.
(a)
Dilute hydrochloric acid or nitric acid
(b)
Carbon/charcoal
(c)
To absorb unreacted CO2.
(d)
(i)
CaCO3(s) + 2H+(aq)
(ii)
C(s) + CO2(g)
(iii)
2NaOH(aq) + CO2(g) −
2CO(g)
or 2OH (aq) + CO2(g) (e)
Ca2+(aq) + CO2(g) + H2O(l) Na2CO3(aq) + H2O(l); CO32−(aq) + H2O(l)
Disconnect flask R from the combustion tube Q and pass the gas into limewater. The milkiness of limewater indicates that some CO2 passes out without changing into CO.
11.
12.
(a)
2C8H18(l) + 25O2(g)
(b)
6.6 mol
(c)
9.9 × 103 dm3
(d)
2.3 × 103 g
(e)
0.31 g
16CO2(g) + 18H2O(l)
Temperature can be assumed to be about the same since the three places are near the Equator. Rates of corrosion are different due to different environments and therefore different amounts of pollutants.
Amount of pollutants is the greatest in an industrial area (place C) with all its industrial plants, factories and ©Aristo Educational Press Ltd. 2004
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motor cars. Amount of pollutants is the least in rural area (place B), where there are no industrial plants and few motor cars. Amount of pollutants is medium in urban area (place A) due to the large number of motor cars. 13.
(a)
Sulphur dioxide is the main pollutant which causes acid rain. Coal-fired power stations in Hong Kong are major sources of sulphur dioxide. To greatly reduce the amount of sulphur dioxide given out, more expensive high-grade fuel (with low sulphur content) should be used. Also, the power stations should be installed with scrubbers. However, the installation and maintenance cost a lot of money. The price of electricity would surely go up.
(b)
Some would be willing to pay, some would not. Some people are well aware of the importance of environmental protection. However, others may think that the acid rain problem is not yet serious in Hong Kong at present, and it is not worthwhile to pay any additional charges.
14.
(a)
Coal is used as fuel in the industrial plant. When the fuel is burnt, the sulphur it contains turns to sulphur dioxide. Besides, some nitrogen dioxide is also produced during burning. Sulphur dioxide and nitrogen dioxide emitted from the industrial plant escape into the atmosphere directly above and are blown by the wind from the southwest. These pollutants combine with rainwater to form acid rain (which is likely to have a pH of 4) that falls on X.
(b)
Y. Not at X. The acid rain would harm the rice. Y is near a pier (ease of transportation).
15.
(a)
If the atmosphere was thicker, we would have more of an insulating ‘blanket’ to provide a thermal balance. As a result: the average daytime temperature would be lower.
(b)
If the atmosphere was thicker, we would have more of an insulating ‘blanket’ to provide a thermal balance. As a result: the average nighttime temperature would be higher.
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17.
(a)
Percentage of the solar energy falling on the Earth
16.
(b)
Using solar heating panels, mirrors and solar cells.
(a)
Liquid; size of fuel tanks can be much smaller
(b)
Water; no
(c)
Strictly speaking, the answer is no. This is because hydrogen produces very small amounts of nitrogen oxides during its combustion. However, hydrogen causes far less pollution than fossil fuels do.
18.
Reflected back into space
Heating up the atmosphere
Powering the water cycle
Heating the surface of the Earth
(a)
Coal
(b)
Oil
(c)
Consumption of coal has decreased greatly.
(d)
Nuclear
(e)
Rapid growth of industry and number of motor vehicles.
©Aristo Educational Press Ltd. 2004
Powering renewable energy sources
- 17 -
(a)
CO2 level (ppm)
19.
(b)
(i)
CO2 levels have increased.
(ii)
CO2 levels at present = 385 ppm
(iii)
No.
(iv)
The prediction nearest the last measured datum would be most accurate. The rate of CO2
2010 = 395 ppm
2050 = 483 ppm
build-up in the atmosphere may change from the previous rates. The further into the future we extrapolate the graph, the more uncertain our prediction would be.
20.
(v)
Same rate of increase of CO2 levels.
(vi)
Year fires, climate etc. Change in amounts of fossil fuels burnt, forest
Collecting the spilt oil using a boom / applying bioremediation / spray the spilt oil with detergents to change it into tiny droplets (any two)
21.
(a)
50 years
(b)
Both heat water to give steam. The steam drives turbines to generate electricity. Nuclear power station Advantages: Clean (or relatively small volumes of fuels are needed) Disadvantages: It may be disastrous if there is a leakage of radioactivity (or special safety measures must be taken to dispose of radioactive waste) Coal-fired power station Advantage: Cheap fuel (or coal readily available) Disadvantage: Production of a large amount of sulphur dioxide
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22.
(a)
Increasing
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(b)
Petroleum
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(c)
(i)
Petroleum, natural gas and coal
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(ii) (d)
Yes
The demand for natural gas increases rapidly. By 2015, natural gas would surpass coal to become the second most important energy source. Petroleum will still remain the first.
(e)
Nuclear power Reasons: (1)
The public have become increasingly aware of the potential dangers associated with
nuclear power. Many people object to building of new nuclear plants. (2)
Keen competition in the energy market (the main competitor being power stations
generating electricity from natural gas)
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CHAPTER 35
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Alcohols
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1.
D
2.
C
3.
D
4.
D
5.
C
6.
C
7.
(1)
Ethanol is miscible with water and many non-aqueous solvents.
(2)
It can dissolve both water-soluble and water-insoluble solutes.
(3)
Being volatile (b.p. = 78°C), it evaporates quickly, leaving the solutes behind.
8.
(a)
Add Na2CO3(aq): propanoic acid gives a colourless gas (CO2), whereas propan-1-ol does not.
(b)
Alkanols are usually identified by the esters they form, as those compounds have pleasant, fruity smells. Mix the substance under test with an alkanoic acid and a little concentrated sulphuric acid. Heat the mixture gently for one or two minutes. If the vapour evolved has a pleasant fruity smell, then the substance under test should be an alkanol.
9.
10.
(a)
CH3CH2CH2CH2OH
(b)
Melting point / boiling point / solubility in water (any two)
(a)
Ethanoic acid
(b)
Heat ethanoic acid and ethanol in the presence of a little concentrated sulphuric acid for 2 or 3 minutes.
(c)
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11.
12.
(a)
Oxidation
(b)
Acidified potassium dichromate
(c)
(i)
Ethyl ethanoate
(ii)
Sweet fruity smell
(iii)
As a catalyst to speed up the reaction
(a)
CH3CH2COOH
CH3CH2CH2CH2CH = CH2
CH3(CH2)4CH3
CH3CHCH3 OH
(b)
Add water (only propanoic acid and propan-2-ol are soluble); then add Na2CO3(s) (only propanoic acid gives colourless gas bubbles (CO2)).
Add KMnO4(aq)/H+(aq) to the remaining two liquids (only hex-1-ene decolorizes the solution added). 13.
(a)
HCOOH + CH3CH2OH
HCOOCH2CH3 + H2O
(b)
Ethyl methanoate; ester
(c)
No
(d)
Add a little conc. sulphuric acid as catalyst; heat the mixture
(e)
(i)
CH3COOH ethanoic acid CH3CH2OH ethanol
(ii)
CH3COOH ethanoic acid CH3CH2CH2OH propan-1-ol
(iii)
CH3CH2COOH propanoic acid CH3CH2OH ethanol
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CHAPTER 36
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Plastics
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1.
B
2.
D
3.
A
4.
B
5.
C
6.
C
7.
D
8.
D
9.
C
10.
B
11.
D
12.
B
13.
C
14.
A
15.
D
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16.
(a) (b)
(i)
Plastic C. It is very flexible.
(ii)
Non-poisonous
Plastic D. It can withstand high temperatures (up to 1350°C). It does not burn and it has a high strength.
(c)
Plastic A. It is highly transparent and is stiff.
17.
Article Camera lens
New plastic material (a) ________
Old material glass
Advantages/disadvantages of plastic and older material (b) Perspex ______________________________________ can be easily moulded and will not break
Perspex
easily, but it can be scratched more easily than ______________________________________ glass.
______________________________________
Stockings
nylon Cotton
(c) ________
Nylon is not attacked by moth, but it does not (d) allow ______________________________________ sweat to evaporate through it easily. Thus it would be uncomfortable to wear nylon stockings in hot weather. Cotton is attacked by moth, but it ______________________________________ has moisture-absorbing properties and is more comfortable to wear. ______________________________________
______________________________________ ______________________________________ ______________________________________ ______________________________________ Covering for electrical cable
PVC
Disposable cup
expanded polystyrene
rubber
PVC is cheaper and more resistant to weathering
(e) than ______________________________________ rubber. ______________________________________ ______________________________________
waxed paper
Expanded polystyrene cup can be used to hold
(f) hot ______________________________________ or cold water, but waxed paper cup would ______________________________________ become soft when hot. ______________________________________ Polythene not easily broken, glass easily broken
Milk bottle (for feeding babies)
polythene
Handle of frying pan
phenol-methanal wood
Glass
(h) ______________________________________
(g) ________ ______________________________________ ______________________________________ Phenol-methanal does not catch fire; wood can
(i) burn ______________________________________ and is easily charred. ______________________________________
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18.
(a)
A polymer is a compound which consists of very large molecules formed by joining many small molecules repeatedly.
(b)
(i)
Starch, rubber, silk
(ii)
Nylon, urea-methanal
(iii)
Styrene
(iv)
Sucrose, olive oil, margarine, glass, ethane
19.
20.
21.
(a)
Condensation
(b)
Addition
(c)
Substitution
(d)
Addition polymerization
(e)
Condensation polymerization
(a)
C
(b)
Possess a carbon-carbon double bond
(c)
B and D; F
(d)
One of the monomers must have at least two reactive sites in a molecule.
(a)
(i)
(ii)
(iii)
addition polymerization
(iv)
(b)
(i)
(ii) (iii)
and condensation polymerization (iv)
©Aristo Educational Press Ltd. 2004
none
or water (or hydrogen chloride)
- 31 -
(c) (i)
(ii) (iii) (d)
(e)
22.
23.
addition polymerization
(iv)
none
(ii) addition polymerization
(i) (iii)
water (or hydrogen chloride)
(ii)
(i) (iii)
(f)
condensation polymerization (iv)
(i) (iii)
or
(iv)
none
(ii) addition polymerization
(iv)
none
(a)
Natural; plant origin; carbohydrate; condensation polymer
(b)
Synthetic; condensation polymer; thermoplastic
(c)
Synthetic; hydrocarbon; addition polymer; thermoplastic
(d)
Natural; animal origin
(e)
Synthetic; contains nitrogen; condensation polymer; thermosetting
(a)
(i)
Iron can be removed by using a magnet.
(ii)
Plastics will float if the refuse is mixed with water (note that the paper will eventually sink as it soaks up water).
(b)
(i)
The bricks can be made easily because plastics can be melted to shape them. Also, plastics are poor conductors of heat and so insulate the building from heat loss.
(ii)
Separation of pure polythene would allow recycling to make more polythene rather than less valuable ‘plastic alloy’ (made from mixtures of plastics) which has fewer uses.
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24.
(a) (b)
Condensation polymerization
(c)
Addition polymerization
(d)
Thin sheets of nylon, instead of long nylon thread, would be resulted.
(e)
Fishing lines by extrusion moulding. (Other answers may also be given.)
(f)
Thermal properties. Urea-methanal is a thermoset while nylon is a thermoplastic.
(g)
Cross-links (strong covalent bonds) are present among urea-methanal molecules. In nylon only weak van der Waals’ forces are present.
(h) 25.
Compression moulding
(a) (b)
26.
(c)
Chloroethene
(d)
Vinyl chloride
(e)
Making floor tiles / pipe / raincoats / shower curtains (any one)
(a)
Polythene
(b) (c)
Ethane-diol
(d)
Addition polymerization
(e)
Making plastic bags / wrapping film / food boxes (any one)
(f)
27.
(g)
Thermoplastic
(h)
Condensation polymerization
(i)
Making textile fibres / sails
(1)
Light weight but high strength
(2)
Chemically unreactive
(3)
Moulded easily
(Other answers may be accepted.)
©Aristo Educational Press Ltd. 2004
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CHAPTER 37 Detergents 1.
A
2.
D
3.
C
4.
B
5.
C
6.
A
7.
D
8.
C
9.
C
10.
A
11.
D
12.
(a)
Their chief source is triesters in animal fats and vegetable oils.
(b)
Low m.p. (b.p.)
(c)
No; stearic acid is insoluble in water
(d)
Although both are ionic salts having a hydrophobic hydrocarbon tail and a hydrophilic ionic head, the hydrophobic tail in sodium ethanoate is too short to allow detergent action.
(e)
(i)
No; stearic acid (having no detergent properties) is displaced out:
CH3(CH2)16COO−(aq) + H+(aq) (ii)
CH3(CH2)16COOH(s)
No; insoluble scum formed: 2CH3(CH2)16COO−(aq) + Ca2+(aq) −
2+
2CH3(CH2)16COO (aq) + Mg (aq) (f)
[CH3(CH2)16COO]2Ca(s) OR [CH3(CH2)16COO]2Mg(s)
Stearic acid is not easily available in nature compared with fats and oils. Soap is manufactured by
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alkaline hydrolysis of natural fats and oils. 13.
(a)
No. A soapless detergent may or may not form lather in water. It is so called to distinguish from soapy detergents (soaps).
(b)
(i)
Both consist of a hydrophobic tail and a hydrophilic head.
−COO− is the hydrophilic part in soaps but not in soapless detergents.
(ii) (c) (ii)
(i)
Hydrocarbons
Conc. H2SO4, followed by NaOH (d)
(ii)
(i)
B
B (e)
No. It has branched chains and is non-biodegradable, thus causing foaming at sewage works and in rivers. Water life will be killed.
14.
(a)
We can tell whether a solution is hard or soft from the height of the lather formed in the experiment.
Lather with a height of 5 cm is formed in distilled water. A liquid with a height of 5 cm high (or slightly less) is considered as soft. A liquid with no lather (or very little lather) is considered as hard. (b)
Soft water
(c)
Dilute sodium chloride solution is soft.
Sea water is hard. Sea water contains appreciable concentration of magnesium salts in addition to sodium chloride. (d)
Yes. It contains appreciable concentration of Ca2+(aq) ions.
(e)
Hard water
(f)
A lather (probably a few cm high) is formed in every liquid, with approximately the same height in each case.
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CHAPTER 38 Separation of mixtures 1.
2.
(a)
C
(b)
A
(c)
B
(d)
D
(e)
E
(a)
B
(b)
A
(c)
C
(d)
D
(e)
C
3.
C
4.
Heat, collect X (as sublimate) on a cool surface; put the remaining solid into hot water, filter, wash residue with distilled water, dry residue (Y); evaporate filtrate to dryness (or crystallize) to obtain Z.
5.
No. Add solid to distilled water and stir well. Filter and evaporate the filtrate to dryness by heating. See whether any solid is left.
6.
(a)
The receiver test tube should never be stoppered, otherwise the methylated spirit will be heated inside a closed system, which is a very dangerous practice.
(b)
The receiver test tube should be placed in a beaker of cold water to condense the hot vapour given out.
(c)
As methylated spirit is flammable, it should not be heated by a naked flame; a hot water bath should be used instead.
7.
(d)
Test tube A should not be filled to more than 1/3 of its capacity.
(a)
Insoluble in water
(b)
Black and blue; black and red
(c)
Blue, red and orange
(d)
Separation, purification and identification
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CHAPTER 39 Detection of substances 1.
E
2.
C
3.
D
4.
D
5.
B
6.
A
7.
F
8.
A
9.
D
10.
A
11.
C
12.
B
13.
A
14.
A
15.
(a)
White precipitate is formed.
Ag (aq) + Cl−(aq) +
(b)
AgCl(s)
White precipitate is formed. Ba2+(aq) + SO42−(aq)
(c)
BaSO4(s)
Blue gelatinous precipitate is formed.
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Cu2+(aq) + 2OH−(aq)
Cu(OH)2(s)
16.
Test Appearance
Observations White solid
Inference Cation resulted from Group I or II (a) _____________________________ elements
_____________________________ _____________________________ Heating Flame test
No change Brilliant golden yellow flame
Cation should be Na+ (b) _____________________________
_____________________________ _____________________________ Add dilute hydrochloric acid
Solid dissolves, no effervescence
Neither CO32− nor SO32− present
(c) _____________________________ _____________________________ _____________________________
Add dilute hydrochloric acid followed by the addition of barium chloride solution
No precipitate
Add dilute nitric acid and silver nitrate solution
White precipitate
No SO42− present (d) _____________________________
_____________________________ _____________________________ Anion should be Cl− (e) _____________________________
_____________________________ _____________________________ Therefore, the compound should be sodium chloride. 17.
(a)
Add magnesium sulphate solution to the substances. Sodium carbonate forms a white precipitate while sodium hydrogencarbonate does not.
(b)
Add dilute hydrochloric acid to the substances. Effervescence is observed for calcium carbonate but not for calcium hydroxide.
(c)
Add dilute hydrochloric acid to the substances. Sodium sulphite gives out colourless sulphur dioxide gas while sodium sulphate does not.
(d)
Add acidified silver nitrate solution to the substances. Sodium chloride forms a white precipitate while sodium nitrate does not.
(e)
Add acidified silver nitrate solution to the substances. Potassium chloride forms a white precipitate while potassium iodide gives a yellow precipitate.
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(f)
Add acidified silver nitrate solution to the substances. Sodium bromide forms a pale yellow precipitate while sodium nitrate does not.
(g)
Add dilute hydrochloric acid to the substances. Zinc carbonate gives out colourless gas and form a colourless solution. Lead(II) carbonate gives out colourless gas and form a cloudy solution.
(h)
Sodium nitrate gives a brilliant golden yellow flame in flame test while ammonium nitrate does not.
(i)
Add dilute hydrochloric acid to the substances. Copper(II) oxide dissolves to form a blue solution while iron(III) oxide dissolves to form a yellow solution.
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FOSSIL FUELS AND CARBON COMPOUNDS
Chapter 30 Chapter 31
Chapter 35
Fossil fuels 2 Homologous series, structural formulae and naming of carbon compounds 4 Alkanes and alkenes 6 Consequences of using fossil fuels (Part One): Burning of fuels 8 Consequences of using fossil fuels (Part Two): Environmental problems associated with the use of fossil fuels 9 Alcohols 14
PART XI
PLASTICS AND DETERGENTS
Chapter 36 Chapter 37
Plastics Detergents
PART X
DETECTION AND ANALYSIS
Chapter 38 Chapter 39
Separation of mixtures Detection of substances
Chapter 32 Chapter 33 Chapter 34
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23 24
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CHAPTER 30 Fossil fuels 1.
B
2.
D
3.
B
4.
A
5.
A
6.
C
7.
B
8.
C
9.
A
10.
D
11.
(a)
It is a complex mixture of alkanes. Some of the higher alkanes dissolve in liquid oil to form a solution; besides, the various compounds present lower the melting points of each other.
(b)
Fractional distillation
(c)
1
(d)
1 (refinery gas); 2 (petrol; naphtha); 3 (kerosene); 4 (gas oil)
(e)
Most of the residue is burnt directly as fuel oil in large furnaces such as those in power stations or big ships. A small proportion of it is vacuum distilled to give lubricating oils, waxes and bitumen (for surfacing roads).
(f)
Fraction 2; petrol as motor car fuel, naphtha to produce town gas and alkenes (for preparing many useful chemicals)
(g)
It is immiscible with water and has a density less than 1 g cm−3, hence it forms a layer on the surface of water, suffocating the larvae. Fraction 2 would not be suitable, as it is volatile and will easily evaporate away.
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12.
(a)
Boiling point in °C Percentage (by mass) of crude oil which boils off
below 40
40 − 170
170 − 250
250 − 350
above 350
2
35
11
30
22
(b)
Percentage (by mass) of crude oil which boils off crude oil which boils off
35 30 25 20 15 10 5 0
below 40
40 − 170
170 − 250 250 − 350 above 350 Boiling point (°C)
(c)
40 − 170°C
(d)
North Sea oil
(e)
Yes. North Sea oil contains a higher percentage of the 40 − 170°C fraction (the most valuable fraction).
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CHAPTER 31
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Homologous series, structural formulae and naming of carbon compounds 1.
C
2.
D
3.
A
4.
B
5.
B
6.
C
7.
A
8.
B
9.
A
10.
D
11.
D
12.
B
13.
B
14.
D
15.
(a)
C, D, E
(b)
C, D
(c)
E
(d)
A, B
(e)
A, C, E
(f)
B, D
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16.
(a)
(b)
(c)
(d)
(e)
(f)
17.
A and F
18.
(a)
Pentane
(b)
1-chloro-2-methylbutane
(c)
1-bromo-2,2-dimethylpropane
(d)
1,1,2,3-tetrachloro-2-methylpropane
(e)
Propene
(f)
But-1-ene
(g)
3,3,3-trichloropropene
(h)
3-chlorobutan-1-ol
(i)
2-chloropropanoic acid
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CHAPTER 32
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Alkanes and alkenes 1.
D
2.
B
3.
D
4.
A
5.
C
6.
A
7.
B
8.
C
9.
A
10.
B
11.
B
12.
(a)
A substitution reaction is a chemical change in which an atom (or a group of atoms) of an organic molecule is replaced by another atom (or group of atoms).
(b)
CH4 + Cl2 CH3Cl + Cl2
CH2Cl2 + HCl
CH2Cl2 + Cl2
CHCl3 + HCl
CHCl3 + Cl2 13.
CH3Cl + HCl
CCl4 + HCl
Both are a family of substances, which show gradation in physical properties and similarity in chemical properties.
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14.
(a)
Breaking large organic molecules into smaller ones by heating in the absence of air.
(b)
C5 − C10 alkanes
(c)
CH3(CH2)4CH3
CH3CH2CH2CH3 + CH2=CH2;
CH3(CH2)4CH3
CH3CH2CH3 + CH3CH=CH2 (Other answers may be given.)
(d)
To produce alkenes which serve as starting materials for preparing a great variety of organic compounds.
15.
(e)
To produce extra petrol.
(a)
(i)
Carbon dioxide (CO2), water
(ii)
Toxic gas, carbon monoxide, will be produced in incomplete combustion when there is not enough oxygen.
(b)
16.
(i)
Cracking
(ii)
Useful substances such as petrol and alkenes can be obtained.
(a)
Alkene
(b)
(i)
CH2 = CH2 + Cl2
CH2ClCH2Cl
(ii)
17.
18.
(c)
Ethene can decolorize an acidified solution of potassium permanganate, while hexane cannot.
(a)
Cracking
(b)
Heavy oil fractions such as fuel oil or larger alkanes
(a)
Molecular formula: C3H6
(b)
1,2-dibromopropane
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CHAPTER 33
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Consequences of using fossil fuels (Part One): Burning of fuels
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1.
D
2.
A
3.
D
4.
B
5.
C
6.
B
7.
D
8.
B
9.
C
10.
(i)
(a), (b), (c)
(ii)
(a), (f)
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CHAPTER 34
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Consequences of using fossil fuels (Part Two): Environmental problems associated with the use of fossil fuels
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1.
A
2.
B
3.
B
4.
D
5.
D
6.
B
7.
A
8.
D
9.
C
10.
(a)
Dilute hydrochloric acid or nitric acid
(b)
Carbon/charcoal
(c)
To absorb unreacted CO2.
(d)
(i)
CaCO3(s) + 2H+(aq)
(ii)
C(s) + CO2(g)
(iii)
2NaOH(aq) + CO2(g) −
2CO(g)
or 2OH (aq) + CO2(g) (e)
Ca2+(aq) + CO2(g) + H2O(l) Na2CO3(aq) + H2O(l); CO32−(aq) + H2O(l)
Disconnect flask R from the combustion tube Q and pass the gas into limewater. The milkiness of limewater indicates that some CO2 passes out without changing into CO.
11.
12.
(a)
2C8H18(l) + 25O2(g)
(b)
6.6 mol
(c)
9.9 × 103 dm3
(d)
2.3 × 103 g
(e)
0.31 g
16CO2(g) + 18H2O(l)
Temperature can be assumed to be about the same since the three places are near the Equator. Rates of corrosion are different due to different environments and therefore different amounts of pollutants.
Amount of pollutants is the greatest in an industrial area (place C) with all its industrial plants, factories and ©Aristo Educational Press Ltd. 2004
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motor cars. Amount of pollutants is the least in rural area (place B), where there are no industrial plants and few motor cars. Amount of pollutants is medium in urban area (place A) due to the large number of motor cars. 13.
(a)
Sulphur dioxide is the main pollutant which causes acid rain. Coal-fired power stations in Hong Kong are major sources of sulphur dioxide. To greatly reduce the amount of sulphur dioxide given out, more expensive high-grade fuel (with low sulphur content) should be used. Also, the power stations should be installed with scrubbers. However, the installation and maintenance cost a lot of money. The price of electricity would surely go up.
(b)
Some would be willing to pay, some would not. Some people are well aware of the importance of environmental protection. However, others may think that the acid rain problem is not yet serious in Hong Kong at present, and it is not worthwhile to pay any additional charges.
14.
(a)
Coal is used as fuel in the industrial plant. When the fuel is burnt, the sulphur it contains turns to sulphur dioxide. Besides, some nitrogen dioxide is also produced during burning. Sulphur dioxide and nitrogen dioxide emitted from the industrial plant escape into the atmosphere directly above and are blown by the wind from the southwest. These pollutants combine with rainwater to form acid rain (which is likely to have a pH of 4) that falls on X.
(b)
Y. Not at X. The acid rain would harm the rice. Y is near a pier (ease of transportation).
15.
(a)
If the atmosphere was thicker, we would have more of an insulating ‘blanket’ to provide a thermal balance. As a result: the average daytime temperature would be lower.
(b)
If the atmosphere was thicker, we would have more of an insulating ‘blanket’ to provide a thermal balance. As a result: the average nighttime temperature would be higher.
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17.
(a)
Percentage of the solar energy falling on the Earth
16.
(b)
Using solar heating panels, mirrors and solar cells.
(a)
Liquid; size of fuel tanks can be much smaller
(b)
Water; no
(c)
Strictly speaking, the answer is no. This is because hydrogen produces very small amounts of nitrogen oxides during its combustion. However, hydrogen causes far less pollution than fossil fuels do.
18.
Reflected back into space
Heating up the atmosphere
Powering the water cycle
Heating the surface of the Earth
(a)
Coal
(b)
Oil
(c)
Consumption of coal has decreased greatly.
(d)
Nuclear
(e)
Rapid growth of industry and number of motor vehicles.
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Powering renewable energy sources
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(a)
CO2 level (ppm)
19.
(b)
(i)
CO2 levels have increased.
(ii)
CO2 levels at present = 385 ppm
(iii)
No.
(iv)
The prediction nearest the last measured datum would be most accurate. The rate of CO2
2010 = 395 ppm
2050 = 483 ppm
build-up in the atmosphere may change from the previous rates. The further into the future we extrapolate the graph, the more uncertain our prediction would be.
20.
(v)
Same rate of increase of CO2 levels.
(vi)
Year fires, climate etc. Change in amounts of fossil fuels burnt, forest
Collecting the spilt oil using a boom / applying bioremediation / spray the spilt oil with detergents to change it into tiny droplets (any two)
21.
(a)
50 years
(b)
Both heat water to give steam. The steam drives turbines to generate electricity. Nuclear power station Advantages: Clean (or relatively small volumes of fuels are needed) Disadvantages: It may be disastrous if there is a leakage of radioactivity (or special safety measures must be taken to dispose of radioactive waste) Coal-fired power station Advantage: Cheap fuel (or coal readily available) Disadvantage: Production of a large amount of sulphur dioxide
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22.
(a)
Increasing
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(b)
Petroleum
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(c)
(i)
Petroleum, natural gas and coal
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(ii) (d)
Yes
The demand for natural gas increases rapidly. By 2015, natural gas would surpass coal to become the second most important energy source. Petroleum will still remain the first.
(e)
Nuclear power Reasons: (1)
The public have become increasingly aware of the potential dangers associated with
nuclear power. Many people object to building of new nuclear plants. (2)
Keen competition in the energy market (the main competitor being power stations
generating electricity from natural gas)
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CHAPTER 35
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Alcohols
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1.
D
2.
C
3.
D
4.
D
5.
C
6.
C
7.
(1)
Ethanol is miscible with water and many non-aqueous solvents.
(2)
It can dissolve both water-soluble and water-insoluble solutes.
(3)
Being volatile (b.p. = 78°C), it evaporates quickly, leaving the solutes behind.
8.
(a)
Add Na2CO3(aq): propanoic acid gives a colourless gas (CO2), whereas propan-1-ol does not.
(b)
Alkanols are usually identified by the esters they form, as those compounds have pleasant, fruity smells. Mix the substance under test with an alkanoic acid and a little concentrated sulphuric acid. Heat the mixture gently for one or two minutes. If the vapour evolved has a pleasant fruity smell, then the substance under test should be an alkanol.
9.
10.
(a)
CH3CH2CH2CH2OH
(b)
Melting point / boiling point / solubility in water (any two)
(a)
Ethanoic acid
(b)
Heat ethanoic acid and ethanol in the presence of a little concentrated sulphuric acid for 2 or 3 minutes.
(c)
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11.
12.
(a)
Oxidation
(b)
Acidified potassium dichromate
(c)
(i)
Ethyl ethanoate
(ii)
Sweet fruity smell
(iii)
As a catalyst to speed up the reaction
(a)
CH3CH2COOH
CH3CH2CH2CH2CH = CH2
CH3(CH2)4CH3
CH3CHCH3 OH
(b)
Add water (only propanoic acid and propan-2-ol are soluble); then add Na2CO3(s) (only propanoic acid gives colourless gas bubbles (CO2)).
Add KMnO4(aq)/H+(aq) to the remaining two liquids (only hex-1-ene decolorizes the solution added). 13.
(a)
HCOOH + CH3CH2OH
HCOOCH2CH3 + H2O
(b)
Ethyl methanoate; ester
(c)
No
(d)
Add a little conc. sulphuric acid as catalyst; heat the mixture
(e)
(i)
CH3COOH ethanoic acid CH3CH2OH ethanol
(ii)
CH3COOH ethanoic acid CH3CH2CH2OH propan-1-ol
(iii)
CH3CH2COOH propanoic acid CH3CH2OH ethanol
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CHAPTER 36
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Plastics
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1.
B
2.
D
3.
A
4.
B
5.
C
6.
C
7.
D
8.
D
9.
C
10.
B
11.
D
12.
B
13.
C
14.
A
15.
D
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16.
(a) (b)
(i)
Plastic C. It is very flexible.
(ii)
Non-poisonous
Plastic D. It can withstand high temperatures (up to 1350°C). It does not burn and it has a high strength.
(c)
Plastic A. It is highly transparent and is stiff.
17.
Article Camera lens
New plastic material (a) ________
Old material glass
Advantages/disadvantages of plastic and older material (b) Perspex ______________________________________ can be easily moulded and will not break
Perspex
easily, but it can be scratched more easily than ______________________________________ glass.
______________________________________
Stockings
nylon Cotton
(c) ________
Nylon is not attacked by moth, but it does not (d) allow ______________________________________ sweat to evaporate through it easily. Thus it would be uncomfortable to wear nylon stockings in hot weather. Cotton is attacked by moth, but it ______________________________________ has moisture-absorbing properties and is more comfortable to wear. ______________________________________
______________________________________ ______________________________________ ______________________________________ ______________________________________ Covering for electrical cable
PVC
Disposable cup
expanded polystyrene
rubber
PVC is cheaper and more resistant to weathering
(e) than ______________________________________ rubber. ______________________________________ ______________________________________
waxed paper
Expanded polystyrene cup can be used to hold
(f) hot ______________________________________ or cold water, but waxed paper cup would ______________________________________ become soft when hot. ______________________________________ Polythene not easily broken, glass easily broken
Milk bottle (for feeding babies)
polythene
Handle of frying pan
phenol-methanal wood
Glass
(h) ______________________________________
(g) ________ ______________________________________ ______________________________________ Phenol-methanal does not catch fire; wood can
(i) burn ______________________________________ and is easily charred. ______________________________________
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18.
(a)
A polymer is a compound which consists of very large molecules formed by joining many small molecules repeatedly.
(b)
(i)
Starch, rubber, silk
(ii)
Nylon, urea-methanal
(iii)
Styrene
(iv)
Sucrose, olive oil, margarine, glass, ethane
19.
20.
21.
(a)
Condensation
(b)
Addition
(c)
Substitution
(d)
Addition polymerization
(e)
Condensation polymerization
(a)
C
(b)
Possess a carbon-carbon double bond
(c)
B and D; F
(d)
One of the monomers must have at least two reactive sites in a molecule.
(a)
(i)
(ii)
(iii)
addition polymerization
(iv)
(b)
(i)
(ii) (iii)
and condensation polymerization (iv)
©Aristo Educational Press Ltd. 2004
none
or water (or hydrogen chloride)
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(c) (i)
(ii) (iii) (d)
(e)
22.
23.
addition polymerization
(iv)
none
(ii) addition polymerization
(i) (iii)
water (or hydrogen chloride)
(ii)
(i) (iii)
(f)
condensation polymerization (iv)
(i) (iii)
or
(iv)
none
(ii) addition polymerization
(iv)
none
(a)
Natural; plant origin; carbohydrate; condensation polymer
(b)
Synthetic; condensation polymer; thermoplastic
(c)
Synthetic; hydrocarbon; addition polymer; thermoplastic
(d)
Natural; animal origin
(e)
Synthetic; contains nitrogen; condensation polymer; thermosetting
(a)
(i)
Iron can be removed by using a magnet.
(ii)
Plastics will float if the refuse is mixed with water (note that the paper will eventually sink as it soaks up water).
(b)
(i)
The bricks can be made easily because plastics can be melted to shape them. Also, plastics are poor conductors of heat and so insulate the building from heat loss.
(ii)
Separation of pure polythene would allow recycling to make more polythene rather than less valuable ‘plastic alloy’ (made from mixtures of plastics) which has fewer uses.
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24.
(a) (b)
Condensation polymerization
(c)
Addition polymerization
(d)
Thin sheets of nylon, instead of long nylon thread, would be resulted.
(e)
Fishing lines by extrusion moulding. (Other answers may also be given.)
(f)
Thermal properties. Urea-methanal is a thermoset while nylon is a thermoplastic.
(g)
Cross-links (strong covalent bonds) are present among urea-methanal molecules. In nylon only weak van der Waals’ forces are present.
(h) 25.
Compression moulding
(a) (b)
26.
(c)
Chloroethene
(d)
Vinyl chloride
(e)
Making floor tiles / pipe / raincoats / shower curtains (any one)
(a)
Polythene
(b) (c)
Ethane-diol
(d)
Addition polymerization
(e)
Making plastic bags / wrapping film / food boxes (any one)
(f)
27.
(g)
Thermoplastic
(h)
Condensation polymerization
(i)
Making textile fibres / sails
(1)
Light weight but high strength
(2)
Chemically unreactive
(3)
Moulded easily
(Other answers may be accepted.)
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CHAPTER 37 Detergents 1.
A
2.
D
3.
C
4.
B
5.
C
6.
A
7.
D
8.
C
9.
C
10.
A
11.
D
12.
(a)
Their chief source is triesters in animal fats and vegetable oils.
(b)
Low m.p. (b.p.)
(c)
No; stearic acid is insoluble in water
(d)
Although both are ionic salts having a hydrophobic hydrocarbon tail and a hydrophilic ionic head, the hydrophobic tail in sodium ethanoate is too short to allow detergent action.
(e)
(i)
No; stearic acid (having no detergent properties) is displaced out:
CH3(CH2)16COO−(aq) + H+(aq) (ii)
CH3(CH2)16COOH(s)
No; insoluble scum formed: 2CH3(CH2)16COO−(aq) + Ca2+(aq) −
2+
2CH3(CH2)16COO (aq) + Mg (aq) (f)
[CH3(CH2)16COO]2Ca(s) OR [CH3(CH2)16COO]2Mg(s)
Stearic acid is not easily available in nature compared with fats and oils. Soap is manufactured by
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alkaline hydrolysis of natural fats and oils. 13.
(a)
No. A soapless detergent may or may not form lather in water. It is so called to distinguish from soapy detergents (soaps).
(b)
(i)
Both consist of a hydrophobic tail and a hydrophilic head.
−COO− is the hydrophilic part in soaps but not in soapless detergents.
(ii) (c) (ii)
(i)
Hydrocarbons
Conc. H2SO4, followed by NaOH (d)
(ii)
(i)
B
B (e)
No. It has branched chains and is non-biodegradable, thus causing foaming at sewage works and in rivers. Water life will be killed.
14.
(a)
We can tell whether a solution is hard or soft from the height of the lather formed in the experiment.
Lather with a height of 5 cm is formed in distilled water. A liquid with a height of 5 cm high (or slightly less) is considered as soft. A liquid with no lather (or very little lather) is considered as hard. (b)
Soft water
(c)
Dilute sodium chloride solution is soft.
Sea water is hard. Sea water contains appreciable concentration of magnesium salts in addition to sodium chloride. (d)
Yes. It contains appreciable concentration of Ca2+(aq) ions.
(e)
Hard water
(f)
A lather (probably a few cm high) is formed in every liquid, with approximately the same height in each case.
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CHAPTER 38 Separation of mixtures 1.
2.
(a)
C
(b)
A
(c)
B
(d)
D
(e)
E
(a)
B
(b)
A
(c)
C
(d)
D
(e)
C
3.
C
4.
Heat, collect X (as sublimate) on a cool surface; put the remaining solid into hot water, filter, wash residue with distilled water, dry residue (Y); evaporate filtrate to dryness (or crystallize) to obtain Z.
5.
No. Add solid to distilled water and stir well. Filter and evaporate the filtrate to dryness by heating. See whether any solid is left.
6.
(a)
The receiver test tube should never be stoppered, otherwise the methylated spirit will be heated inside a closed system, which is a very dangerous practice.
(b)
The receiver test tube should be placed in a beaker of cold water to condense the hot vapour given out.
(c)
As methylated spirit is flammable, it should not be heated by a naked flame; a hot water bath should be used instead.
7.
(d)
Test tube A should not be filled to more than 1/3 of its capacity.
(a)
Insoluble in water
(b)
Black and blue; black and red
(c)
Blue, red and orange
(d)
Separation, purification and identification
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CHAPTER 39 Detection of substances 1.
E
2.
C
3.
D
4.
D
5.
B
6.
A
7.
F
8.
A
9.
D
10.
A
11.
C
12.
B
13.
A
14.
A
15.
(a)
White precipitate is formed.
Ag (aq) + Cl−(aq) +
(b)
AgCl(s)
White precipitate is formed. Ba2+(aq) + SO42−(aq)
(c)
BaSO4(s)
Blue gelatinous precipitate is formed.
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Cu2+(aq) + 2OH−(aq)
Cu(OH)2(s)
16.
Test Appearance
Observations White solid
Inference Cation resulted from Group I or II (a) _____________________________ elements
_____________________________ _____________________________ Heating Flame test
No change Brilliant golden yellow flame
Cation should be Na+ (b) _____________________________
_____________________________ _____________________________ Add dilute hydrochloric acid
Solid dissolves, no effervescence
Neither CO32− nor SO32− present
(c) _____________________________ _____________________________ _____________________________
Add dilute hydrochloric acid followed by the addition of barium chloride solution
No precipitate
Add dilute nitric acid and silver nitrate solution
White precipitate
No SO42− present (d) _____________________________
_____________________________ _____________________________ Anion should be Cl− (e) _____________________________
_____________________________ _____________________________ Therefore, the compound should be sodium chloride. 17.
(a)
Add magnesium sulphate solution to the substances. Sodium carbonate forms a white precipitate while sodium hydrogencarbonate does not.
(b)
Add dilute hydrochloric acid to the substances. Effervescence is observed for calcium carbonate but not for calcium hydroxide.
(c)
Add dilute hydrochloric acid to the substances. Sodium sulphite gives out colourless sulphur dioxide gas while sodium sulphate does not.
(d)
Add acidified silver nitrate solution to the substances. Sodium chloride forms a white precipitate while sodium nitrate does not.
(e)
Add acidified silver nitrate solution to the substances. Potassium chloride forms a white precipitate while potassium iodide gives a yellow precipitate.
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(f)
Add acidified silver nitrate solution to the substances. Sodium bromide forms a pale yellow precipitate while sodium nitrate does not.
(g)
Add dilute hydrochloric acid to the substances. Zinc carbonate gives out colourless gas and form a colourless solution. Lead(II) carbonate gives out colourless gas and form a cloudy solution.
(h)
Sodium nitrate gives a brilliant golden yellow flame in flame test while ammonium nitrate does not.
(i)
Add dilute hydrochloric acid to the substances. Copper(II) oxide dissolves to form a blue solution while iron(III) oxide dissolves to form a yellow solution.
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