Unit 2 Review, pages 246-253
Knowledge
1. (b)
2. (a)
3. (c)
4. (c)
5. (d)
6. (b)
7. (a)
8. (d)
9. (b)
10. (d)
11. (c)
12. (d)
13. (b)
14. (a)
15. False. In the following chemical equation the 3 in front of O2 is called a coefficient:
2 ZnS + 3 O2 → 2 ZnO + 2 SO2
16. False. Potassium chlorate is heated to produce potassium chloride and oxygen in a
decomposition reaction.
17. True
18. True
19. False. Every spring, mercury disappears from the Arctic atmosphere.
20. False. When potassium chloride and silver nitrate undergo a double displacement reaction,
silver chloride precipitates out of the solution.
21. True
22. True
23. True
24. False. When acting as a leavening agent, the acid and the carbonate compound in baking
powder react with each other when water is added.
25. False. Flash smelting is a type of chemical processing.
26. True
27. (a) (iii)
(b) (iv)
(c) (i)
(d) (ii)
28. (a) (i)
(b) (iv)
(c) (ii)
(d) (iii)
29. Chemical and mathematical equations are alike in that they both use symbols to represent
quantities and show equality. Just as an equals sign relates two sets of quantities in a
mathematical equation, so does an arrow in a chemical equation.
30. To check if a chemical equation is balanced, count the number of atoms of each element on
either side of the arrow. Be sure to use subscripts and coefficients to count the number of atoms
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of each element. If there is the same number of atoms of each element on both sides of the arrow,
the equation is balanced.
31. Melting ice is a physical change and not a chemical change because the identity of the
substance remains the same. Both the ice and the resulting liquid are water. No new substances
are formed in the change.
32. In a synthesis reaction, such as the formation of ammonia from hydrogen and nitrogen, two
simpler reactants combine to form a more complex compound. In a decomposition reaction, such
as the decomposition of ammonia into hydrogen and nitrogen, a complex compound breaks
down into simpler substances. Therefore, synthesis and decomposition reactions, such as those
for ammonia, are reversible reactions.
33. The products of some synthesis reactions depend on the reaction conditions. More than one
product is possible from the same reactants. Solid carbon and oxygen gas, for example, can form
carbon dioxide gas or carbon monoxide gas depending upon the availability of oxygen. Also,
because both gases have similar physical properties, chemical tests would be needed to verify
which gas is produced.
34. As a result of the intense heat produced during plasma gasification, the energy is so great that
the molecules are torn apart and the atoms are forced to ionize.
35. Hydrogen is included in the activity series of metals because it forms a positively charged ion
like a metal.
36. If an element of the reactants is higher on the activity series than the element in a compound
that it is trying to replace, a single displacement reaction will occur.
37. In the single displacement pattern for halogens, the negative halogen ion is displaced whereas
in the pattern used for metals, the positive metal ion is displaced.
38. Bromide ions are stable because each ion has eight valence electrons, which is a stable
electron configuration. Bromine atoms are more reactive because each atom contains only seven
valence electrons, which is an unstable electron configuration.
39. Three factors that affect the solubility of a solute are the type of bonding within the solute,
the states of both substances, and the temperature of the solvent.
40. When sulfides, such as Na2S, react with acids, hydrogen sulfide gas, H2S, is produced.
41. Human health might be affected when incomplete combustion produces the pollutant carbon
monoxide. Soot and other solids and gases can also pollute the air.
42. Hydrocarbons are a type of organic compound. Hydrocarbons are commonly used as fuels.
43. If Bernard Courtois had possessed a large supply of firewood, iodine would not have been
discovered at that time. Firewood does not contain the iodine found in seaweed. Thus, iodine
would not have been released from the seaweed, and its discovery would have been delayed.
44. Magnesium metal burns in air to form magnesium oxide, MgO. Adding water to magnesium
oxide produces magnesium hydroxide, Mg(OH)2, which is a base.
45. Diphosphorus pentoxide is an acidic oxide because it forms an acidic solution when
dissolved in water.
46. (a) The base used to neutralize the sulfuric acid in a battery was sodium hydroxide, NaOH.
(b) An ionic compound and water are the products of a neutralization reaction between an acid
and a hydroxide compound. The cation in the ionic compound is sodium, which must have come
from the hydroxide base.
47. Two main advantages of flash smelting over regular smelting are that it results in reduced
fuel costs and produces less pollution.
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48. (a) The single most important air pollutant released by the mining industry is sulfur dioxide.
(b) Improvements in technology and stricter emission standards have reduced the amount of
sulfur dioxide produced.
49. Using micro-organisms to clean up spilled hydrocarbons may completely destroy the
contamination, but the products include carbon dioxide, which is a greenhouse gas.
50. (a) A compound that is used for the chemical oxidation of contaminants is hydrogen
peroxide, H2O2.
(b) During the oxidation process, contaminants are chemically converted to less hazardous
substances.
51. Using recycled paper instead of wood pulp changes the bleaching process used because
recycled paper has already been through a bleaching process and requires less bleaching.
52. The pulp and paper industry uses a renewable resource (fast-growing trees), recovers and
reuses some of the chemicals necessary to remove lignin, and has replaced chlorine with safer
bleaching chemicals.
Understanding
53. (a) The reactants in the reaction are silicon, Si, and carbon dioxide, CO2.
(b) The products in the reaction are silicon carbide, SiC, and silicon dioxide, SiO2.
(c) The balanced chemical equation for the reaction is:
2 Si + CO2 → SiC + SiO2
54. (a) 2 Al2O3 + 3 C → 4 Al + 3 CO2
(b) 2 Fe(OH)2 + H2O2 → 2 Fe(OH)3
(c) 2 Ag2O → 4 Ag + O2
55. (a) The word equation for photosynthesis is:
sunlight
carbon dioxide + water
glucose
(chlorophyll)
(b) The balanced chemical equation for the photosynthesis reaction is:
6 CO2 + 6 H2O → C6H12O6
56. (a) H2O + K2O → 2 KOH
(b) 2 Ca + O2 → 2 CaO
(c) CaCO3 → CaO + CO2
57. Both equations describe synthesis reactions in which two reactants combine to form a larger
and more complex product. The first reaction can also be classified as a combustion reaction of
carbon. The first synthesis reaction involves only elements as the reactants, whereas the second
synthesis reaction involves only compounds as the reactants. The product of the first reaction is a
non-metallic oxide, a molecular compound, whereas the product of the second reaction is a
hydroxide, an ionic compound.
58. (a) The reaction of mercury and chlorine is a synthesis reaction.
(b) The balanced chemical equation for the photosynthesis reaction is:
Hg(l) + Cl2(g) → HgCl2(s)
59. (a) The reaction is a decomposition reaction of silver nitrate.
(b) 2 AgNO3(s) → 2 AgNO2(s) + O2(g)
60. (a) During plasma gasification, the plasma torch provides the high-energy electrical sparks
called plasmas to establish the high temperature required to burn the garbage.
(b) Two products formed in plasma gasification are syngas and slag. Syngas is an energy-rich
mixture of mostly hydrocarbon and carbon monoxide that can be burned as a fossil fuel to
generate electricity. Slag can be used in road construction.
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61. (a) The reaction between potassium and water is a synthesis reaction.
(b) The word equation for the reaction is:
potassium + water → hydrogen + potassium hydroxide
(c) The balanced chemical equation for the reaction is:
2 K(s) + 2 H2O(l) → 2 KOH(aq) + H2(g)
62. (a) When copper wire is placed in an aluminum nitrate solution, no change will be observed
and the solution remains colourless. Since copper is lower than aluminum on the activity series,
it will not displace aluminum from its compound. Therefore, no reaction will occur.
Cu(s) + Al(NO3)3(aq) → no reaction
(b) When aluminum wire is placed in a copper(II) nitrate solution, the original blue colour of the
copper solution will fade (become less blue) as some copper metal deposits on the aluminum
wire. Since aluminum is higher than copper on the activity series, aluminum will displace the
copper ions from copper nitrate, forming the copper metal. A single displacement reaction will
occur and the resulting solution will become paler.
The balanced chemical equation for the reaction is:
2 Al(s) + 3 Cu(NO3)2(aq) → 2 Al(NO3)3(aq) + 3 Cu(s)
63. (a) Since copper is lower than hydrogen on the activity series, copper will not displace the
hydrogen atoms in water molecules.
Cu(s) + H2O(l) → no reaction
(b) Since calcium is higher than hydrogen on the activity series, calcium will displace the
hydrogen atoms in water molecules. The balanced chemical equation for the reaction is:
Ca(s) + 2 H2O(l) → Ca(OH)2(aq) + H2(g)
(c) Since lithium is higher than hydrogen on the activity series, lithium will displace the
hydrogen atoms in water molecules. The balanced chemical equation for the reaction is:
2 Li(s) + 2 H2O(l) → 2 LiOH(aq) + H2(g)
(d) Since lead is lower than hydrogen on the activity series, lead will not displace the hydrogen
atoms in water molecules.
Pb(s) + H2O(l) → no reaction
64. (a) A double displacement reaction occurs.
(b) The products of the reaction will be silver chloride and nitric acid.
(c) A balanced chemical equation describing the reaction is:
AgNO3(aq) + HCl(aq) → AgCl(s) + HNO3(aq)
65. (a) The precipitate formed during the reaction is lead(II) carbonate.
(b) A balanced chemical equation describing the reaction is:
Pb(NO3)2(s) + Na2CO3(aq) → PbCO3(s) + 2 NaNO3(aq)
66. Complete combustion occurs when the supply of oxygen is plentiful. Incomplete combustion
occurs when the supply of oxygen is limited. Incomplete combustion produces a greater variety
of products than complete combustion.
67. The products of complete combustion can be predicted from the fuel used. For hydrocarbons,
the products are water and carbon dioxide. Incomplete combustion produces a greater variety of
products that are sometimes difficult to predict. The products of incomplete combustion of
hydrocarbons may include, in addition to water and carbon dioxide, carbon monoxide and
carbon.
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68. It is important to keep accurate records during scientific experiments because sometimes
many years pass before uses are found for accidental discoveries. If good records are not kept,
the procedure used to produce the discovery might not be able to be replicated. In addition, the
discovery itself might be forgotten.
69. The accidental discovery of useful products supports the importance of communication
among scientists because an accidental discovery of one scientist might be the research goal of
another scientist. If scientists do not communicate their findings, duplication of effort occurs or
useful products are not recognized.
70. You can use the periodic table to determine whether an element is a metal or a non-metal.
Oxides of non-metals are acidic oxides and oxides of metals are basic oxides.
71. (a) Sodium forms a basic oxide.
(b) Sulfur forms an acidic oxide.
(c) Nitrogen forms an acidic oxide.
(d) Magnesium forms a basic oxide.
(e) Carbon forms an acidic oxide.
(f) Aluminum forms a basic oxide.
72. (a) An effective antacid must neutralize excess stomach acid but not harm human tissue.
(b) Not all bases can be used as antacids. Some bases are too basic and can harm tissues in the
mouth, throat, esophagus, and stomach.
73. (a) Acid mine drainage is the outflow of unusually acidic water from a mine or tailings dump
site to the surrounding water. The acidity of the water can dissolve toxic metals, such as
aluminum, from the rock, and thus contaminate groundwater and aquatic systems.
(b) To minimize the environmental damage caused by mine drainage, calcium carbonate
(limestone) is used to neutralize the acidity of waste water from mining.
74. (a) Electrolysis is used to further purify a metal after smelting.
(b) With the help of an electric current, the positive metal ions migrate and attach to the
negatively charged electrode. The metal builds up on the electrode, and can later be safely
removed or recycled.
75. When a piece of land contains hazardous substances in sufficient concentration to pose a
threat to human health or to the environment, the land is contaminated enough to require
remediation.
76. Four remediation strategies that should be considered when attempting to make contaminated
land safe for use are: (i) do nothing but restrict land use in the area; (ii) cover or encase the
contaminated soil; (iii) excavate the entire site and replace the contaminated soil with clean soil;
and (iv) treat the soil at the site to remove the contaminants.
77. To recover zinc metal from the mine tailings containing zinc compounds, two electrodes are
inserted in the mine tailings and a high voltage is applied across the electrodes. With the aid of
an electric current, the zinc compounds are broken down into ions. The positive zinc ions will
migrate and attach to the negatively charged electrode and the metal zinc will build up there and
be safely removed later.
78. Both a catalyst and a reactant are involved in the chemical reaction. The reactant is consumed
by the reaction to produce the desired product. The catalyst makes the reaction occur faster but is
not consumed and remains unchanged after the reaction. That is, a catalyst can be used over and
over again.
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Analysis and Application
79. One type of evidence of a chemical reaction is the release or absorption of energy. However,
energy is also involved in some physical changes, such as change of state. Another type of
evidence is the production of a gas, but a gas is produced when a liquid boils or evaporates and
changes to a gas. A precipitate is often evidence of a chemical reaction, but a solid forms when a
liquid freezes and becomes a solid. The only definite proof that a chemical change has occurred
is when the products are chemically different from the reactants.
80. (a) The student changed a subscript, thereby changing the nature of the product. Only
coefficients should be changed to balance a chemical equation.
(b) The correct balanced equation for the reaction is:
2 H2 + O2 → 2 H2O
81. (a) A balanced chemical equation describing the reaction is:
2 LiOH + CO2 → Li2CO3 + H2O
(b) Lithium compounds are used to purify air in space vehicles because the mass of lithium is
less than the mass of more common elements, such as sodium.
82. (a) A balanced equation that represents the reaction of sulfur oxide with water is:
SO3(g) + H2O(g) → H2SO4(aq)
(b) The reaction that occurs in (a) is a synthesis reaction.
(c) Sulfur trioxide and related compounds are released into the atmosphere as a result of the
combustion of fossil fuels such as coal and crude oil or industrial processes, such as smelting.
83. The balanced equations for the Ostwald process are:
Step 1. 4 NH3(g) + 5 O2(g) → 4 NO(g) + 6 H2O(g)
Step 2. 2 NO(g) + O2(g) → 2 NO2(g)
Step 3. 3 NO2(g) + H2O(l) → 2 HNO3(aq) + NO(g)
84. (a) 2 NaN3(s) → 2 Na(g) + 3 N2(g)
(b) Decomposition reactions generally require a source of energy, such as a spark or electricity.
Upon impact, a sensor that detects a collision in the airbag will cause an electric spark to begin
the reaction.
85. Similar to metals used for jewellery, platinum would be placed near the bottom of the activity
series of metals, close to the metals gold and silver.
86. (a) A single displacement reaction occurs when potassium is placed in water. Since
potassium is higher than hydrogen on the activity series, potassium will displace the hydrogen
atoms in water molecules.
(b) The bubbles are from the hydrogen gas released during the reaction.
(c) The balanced chemical equation for the displacement reaction is:
2 K(s) + 2 H2O(l) → 2 KOH(aq) + H2(g)
87. (a) The two types of chemical reactions that occur during the baking process are double
displacement (between sodium hydrogen carbonate and tartaric acid) and decomposition (of
carbonic acid).
(b) The balanced chemical equations for the reactions are:
2 NaHCO3(s) + H2C4H4O6(s) → Na2C4H4O6(aq) + 2 H2CO3(aq)
double displacement
H2CO3(aq) → H2O(l) + CO2(g)
decomposition
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88. (a) The anions that would likely react with the nickel and cobalt cations are carbonate,
phosphate, hydroxide, and sulfide as these anions would form a precipitate with nickel and
cobalt.
(b) Answers may vary. Sample answer: To remove nickel and cobalt ions from water, we can
precipitate the ions out of the solution. We can use a safe and soluble compound with the anions
listed in (a), such as sodium carbonate, that would produce an only slightly soluble compound
with the two metals. The nickel and cobalt will react with the soluble compound to form a
precipitate that can be filtered out.
89. The hard water deposits mostly contain carbonates that react with vinegar to produce carbon
dioxide gas and water.
90. (a) The reaction of baking soda and the acid is a double displacement reaction.
(b) The balanced chemical equation for the reaction is:
H2CO3(aq) → H2O(l) + CO2(g)
91. (a) A double displacement reaction occurs when manganese(II) sulfate is added to
ammonium hydroxide.
(b) The balanced chemical equation for the reaction is:
MnSO4(aq) + 2 NH4OH(aq) → Mn(OH)2(s) + (NH4)2SO4(aq)
92. (a) Some advantages of using coal is that it is inexpensive and that it is an abundant fuel that
generates a lot of energy.
(b) Some disadvantages of using coal are that it contains a lot of impurities. The burning of coal
is a major source of greenhouse gas emissions, soot, mercury, and other pollutants.
93. (a) Incomplete combustion is likely to occur in the furnace, since the supply of air and thus
oxygen is limited.
(b) The most likely products from the furnace include water, carbon dioxide, carbon monoxide,
and maybe carbon in the form of soot.
94. Teflon might be used in sports equipment that need a non-sticking coating for sliding or
moving, such as bicycle chains and the bottom of skis or snowboards.
95. The likely pH for a lake affected by acid rain is below 5.6, since normal rain has a pH of
about 5.6.
96. Ethanoic acid is an effective treatment of sodium oxide because sodium oxide is a basic
oxide. It reacts with water to form a base. An acid such as acetic acid will neutralize the base,
lowering the dangerously high pH of the sludge to safe levels. Ethanoic acid is also a safe acid to
use since it is not very acidic.
97. (a) A base is used to treat a bee sting because it will neutralize the acidic bee venom to
reduce pain and swelling.
(b) An acid, such as vinegar (a solution of ethanoic acid), might be used to treat a wasp sting
because it will neutralize the basic wasp venom.
(c) These acid or base treatments might not be effective for treating stings since the acid or base
can only be applied to the surface of the skin whereas the venom is beneath the skin. The acidbase neutralization of the venom might not take place if the acid and base are not in contact.
98. (a) If the pH of the lake is below 6.1, a carbonate compound could be added to raise the pH.
(b) If the pH of the lake is above 8.6, adding an acid will lower the pH.
99. This fact that gold is found in ore as metallic gold, not as gold compounds affects the
processing of gold ore into gold products. Gold can be refined to metallic gold primarily using
physical methods. It does not have to be chemically changed from a gold compound into gold
metal.
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100. Answers may vary. Sample answer: I think refineries are located on the Great Lakes or near
a river or an ocean because transporting heavy raw materials and final products to and from a
refinery is cheaper by water than by road, rail, or air.
101. Answers may vary. Sample answer: I think it was decided to leave the oil on the shore
where it was because the micro-organisms would be necessary for the bioremediation of the area.
If they were removed, the remediation would be much slower.
102. The two principles of green chemistry used when recycling cans and not making new ones
from aluminum ore are to use less energy and to not create waste.
Evaluation
103. (a) The chemical equation describing the reaction is:
4 P + 3 O2 → 2 P2O3
(b) During a chemical reaction, reactant atoms rearrange to form the products. Since there are
only 4 phosphorus atoms in the reactants and each of the product molecules consists of 2
phosphorus atoms, no more than 2 molecules of diphosphorus trioxide can be formed even if
additional oxygen atoms are available.
104. (a) The student was incorrect. A precipitate is often evidence of a chemical reaction, but a
solid forms when water is removed from a solution of the solute. Solid sugar was dissolved in
hot water. When the water was cooled, the solubility of the sugar was lowered so some solid
sugar appeared.
(b) The only true proof that a chemical reaction has occurred is when the products are tested and
found to be chemically different from the reactants.
105. Answers may vary. Students’ answers should include that some gases may escape into the
environment, and that the process requires an initial source of electricity to operate. Sample
answer: Before making a final decision, we would need to know how the electricity is generated,
to decide whether this is a clean source of energy. Since it is a rural location, the garbage will
have to be transported a considerable distance to the facility, which uses fossil fuels. The
transportation of any products should also be considered.
106. Answers may vary. Sample answer: The chosen metal should not react with cold, salty
water. According to the activity series of metals, nickel, tin, lead, and copper are all less reactive
than iron. Lead is very dense, so may not be the best choice for coating the hull. Copper may be
a better choice since it is the least reactive among these metals.
107. Answers may vary. Sample answer: We should check any appliances, such as a stove,
furnace, or hot water heater, where combustion may occur and make sure that the oxygen supply
is not restricted in any way. Carbon monoxide detectors should also be installed, and a barbeque
should only be used outdoors.
108. Answers may vary. Sample answer: I think the results of scientific research should belong
to whoever pays for the research. This means that the accidental discoveries using the results of
the research should belong to the company for which the scientists work.
109. Answers may vary. Sample answer: Most of the acidic oxides are gases at room
temperature. They tend to react with water in the air or dissolve in water to produce an acidic
solution. Carbon dioxide contributes to global warming. High levels of the gas make the ocean
more acidic, which hampers the growth of the shells of many marine organisms. Sulfur oxides
are a major contributor to acid rain due to the formation of droplets of sulfuric acid. Basic oxides
are solids, so they are less likely to react with water in the air. Also, when they do react with
water, they produce a basic solution.
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110. (a) The reaction between hydrogen chloride gas and ammonia gas is not a neutralization
reaction because no water would form as there is no oxygen in the reactants.
(b) Ammonia gas forms a base, ammonium hydroxide, in water. Similarly, hydrogen chloride
gas forms hydrochloric acid in water. When these two solutions mix, a neutralization reaction
occurs. An acid reacts with a base to form an ionic compound and water.
111. (a) Metal ions can be remediated by soil flushing, stabilization and solidification,
electrolysis, chemical oxidation, or bioremediation.
(b) Organic compounds can be remediated by soil flushing, oxidation, or bioremediation.
112. (a) The two principles of green chemistry included in the making of recycled paper products
are to use less energy and to not create waste.
(b) The recycled paper industry will only be successful if it can sell its products. It needs people
who are willing to buy recycled paper at a price that covers the costs.
Reflect on Your Learning
113. Answers may vary. Sample answer: I learned the different types of chemical reactions, and
what happens to the reactants and products during these reaction types. I learned that some
reactions are the reverse of other reactions and that many of the reactions that occur around me
can be classified as one of these reaction types.
114. Answers may vary. Students’ answers may include these evidence of chemical changes: I
felt that my body was warm as it released thermal energy; I saw the change in colour of the fall
leaves; I saw soap scum when I used soap in hard water. Sample answer: After completing this
unit, I would look for these clues that indicate a chemical change has taken place: unexpected
change in colour, energy released or absorbed, a gas produced, and the formation of a precipitate.
115. Answers may vary. Sample answer: I learned that there are new methods of heating garbage
that turn some of it into useful fuel. I learned that even this method forms undesirable wastes. I
would ask whether there are means other than recycling that could be used to reduce the amount
of garbage produced.
116. Answers may vary. Sample answer: I found it interesting that mercury in Arctic air was
even investigated in the first place. The research was important because it might lead to learning
how to remove toxic mercury vapours from other places on Earth. Removing mercury from the
environment reduces the number of toxic pollutants.
117. Answers may vary. Sample answer:
(a) I have used Teflon, Scotchgard, and Super Glue.
(b) I used Teflon to keep food from sticking on a pan while I cooked. My coat was treated with
Scotchgard to help keep it clean. I used Super Glue to fix a broken chair.
(c) My life might be different because cooking would be more difficult, clothes would get dirty
more easily, and some broken items could not be repaired.
118. Answers may vary. Sample answer:
(a) Sources of acidic oxides include manufacturing sites and vehicles.
(b) Technologies, such as catalytic converters in cars, and government regulations, such as
industrial emission controls, both reduce the quantity of acidic oxides produced and prevent their
release into the environment.
(c) If many acidic oxides are produced, they will contaminate the air and form acid precipitation,
increasing the acidity of water sources and damaging plants and buildings.
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119. (a) Adding a base or a carbonate, such as calcium carbonate, to an acidic pool will raise the
pH from 4 to a proper pH.
(b) Adding an acid, such as ethanoic acid, to a spa that is too basic will lower the pH from 9 to a
proper pH.
120. (a) Air pollution can be carried for great distances by prevailing winds, so air pollutants
released by neighbouring countries are important to the air and water quality of any country.
(b) There is less reference to water and land contamination because water and land pollutants
move less easily from one location to another.
121. Burying contaminated soil is not true remediation as the contaminants are still there, in the
ground. Rainwater or groundwater could move the contaminants into local water supplies or
cause them to rise to the surface. True remediation involves decontaminating the land.
122. Answers may vary. Students’ answers should include two green principles and explanations
of how the principles can be implemented in the chosen business. Sample answer: I live near a
medical gas production plant. There is always a smell surrounding the plant and there are lots of
fumes being released from the plant. The plant should try to contain the gases that it expels by
capturing it and containing the gas. It should also try to capture any energy loss due to heat and
use it to generate additional energy or to keep another part of the process running.
Research
123. Answers may vary. Students’ answers should include a chemical equation with the relevant
state symbols. Sample answer: The state symbol (s) is not adequate if it is important that the
structure of a solid is specified. The symbol “amor” (short for amorphous) refers to a solid with
no crystal structure. The symbol “cr” (crystalline) refers to the crystalline form. An example of
when these state symbols might be required would be a reaction involving carbon. If charcoal or
coke is used to refine metals, for example, the description of the reaction should include that an
amorphous form of carbon is used. Crystalline forms of carbon include graphite and diamond.
124. Combustion reactions are those that involve rapid combination with oxygen. Most
commonly, combustion is the rapid oxidation of a fuel. In many combustion reactions, the
products are water and carbon dioxide. An example is the complete combustion of propane,
C3H8, to heat a building:
C3H8(l) + 5 O2(g) → 4 H2O(g) + 3 CO2(g)
Combustion also refers to reactions in which certain elements, such as magnesium, react rapidly
with oxygen, forming a metallic oxide:
2 Mg(s) + O2(g) → 2 MgO(s)
This combustion of magnesium is also a synthesis reaction.
125. Answers may vary. Students’ reports should explain the importance of the Deacon process
and the use of chlorine. Sample answer: The Deacon process involves the oxidation of hydrogen
chloride to produce chlorine and water: 4 HCl(g) + O2(g) → 2 Cl2(g) + 2 H2O(g)
This reaction takes place in the presence of copper(II) chloride catalyst. Although the process
was the main method of producing chlorine for many years, it has been replaced by the
electrolysis of various metallic chlorides. Ironically, much of the chlorine produced is used in the
production of hydrochloric acid.
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126. (a) Answers may vary. Sample answer: Carbon monoxide is produced when there is not
enough oxygen to produce carbon dioxide such as when operating a stove or an internal
combustion engine in an enclosed space, where the supply of oxygen is limited.
(b) A carbon monoxide detector monitors the concentration of carbon monoxide in the air and
will sound an alarm when the concentration exceeds a safe level.
(c) Symptoms of mild poisoning include headaches and shortness of breath. Symptoms of severe
poisoning include dizziness, convulsions, and unconsciousness. The best treatment for carbon
monoxide poisoning is early treatment with pure oxygen.
127. (a) The adhesive in Post-It notes was the accidental discovery of a weak adhesive while
trying to develop a strong adhesive.
(b) CorningWare was made by the repurposing of materials designed to withstand the extreme
temperatures of re-entry of vehicles returning to Earth from space.
128. (a) A buffer solution resists a change in pH when small quantities of acid or base are added
to the solution.
(b) Most cellular functions must occur within a certain range of pH. A buffer system helps
maintain this pH range.
(c) The main buffer solution in human blood contains both carbonic acid, H2CO3, and hydrogen
carbonate ions, HCO3–.
(d) When a small quantity of acid is added to the blood, it reacts with the hydrogen carbonate
ion, forming carbonic acid. The carbonic acid decomposes into carbon dioxide and water, and
the carbon dioxide is removed during respiration. When a small quantity of base is added to the
blood, it reacts with the carbonic acid, increasing the quantity of the hydrogen carbonate ion.
129. Answers may vary. Sample answer:
(a) Some packing peanuts are now made from cornstarch.
(b) Cornstarch is soluble in water, so the peanuts will dissolve and not take up space in landfills.
130. (a) This open-pit gold mine is in northwestern Quebec.
(b) One benefit is that the mining company creates a sustainable development fund for the
community.
(c) Concerns of the community include the proximity of the mine to the town and the need to
relocate the neighbourhood.
(d) The ore of the new mine will be processed in a mill. The processes include cyanidation and
electrowinning, which are chemical processes.
131. (a) About one million cubic metres of sludge was released.
(b) The main components of the sludge were water, iron(III) oxide, aluminum oxide, and silicon
dioxide.
(c) The main components of the sludge are not as dangerous as some of the minor components,
such as sodium oxide and potassium oxide. Several minor components are basic oxides, which
raised the pH to dangerous levels. The sludge was highly corrosive and caused skin burns.
(d) Methods of remediation include physically blocking the sludge from entering various
waterways, using chemicals to remove heavy metals, and using acids to neutralize the bases in
the sludge.
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Unit 2: Chemical Reactions
U2-13