Chapter 3 Review, pages 128–133
Knowledge
1. (c)
2. (d)
3. (a)
4. (c)
5. (d)
6. (a)
7. (d)
8. (a)
9. (a)
10. (c)
11. (b)
12. True
13. True
14. False. Citronella oil, garlic, geranium oil, and peppermint are examples of natural insect
repellents.
15. True
16. False. Of the polar covalent bonds H–F, H–Cl, and H–Br, the most polar is H–F.
17. False. For the polar covalent bond between a silicon atom and a chlorine atom, the partial
charges would be shown as δ+ Si–Cl δ–.
18. True
19. False. Boiling and sublimating are physical changes.
20. False. The strongest intermolecular attractions in nitrogen trifluoride are dipole–dipole
forces.
21. False. Water, H2O, is the only substance on Earth that commonly exists as a solid, a liquid,
and a gas.
22. True
23. (a) (i)
(b) (iii)
(c) (ii)
24. Three categories of beneficial compounds produced by micro-organisms are food, fuel, and
medicines.
25. Four materials that are commonly recycled in many countries are glass, metal, plastic, and
paper.
26. An insect repellent discourages insects from approaching, whereas an insecticide kills them
outright.
27. The United States Army originally developed DEET to protect soldiers fighting in mosquitoinfested regions.
28. (a) Covalent bonds form between atoms.
(b) Ionic bonds form between ions.
(c) Ionic bonds are created by a transfer of valence electrons between entities.
(d) Covalent bonds are created by the sharing of pairs of valence electrons between entities.
(e) Covalent bonds hold together the atoms within molecules.
29. Ionic compounds do not have intermolecular forces because ionic compounds do not consist
of molecules. Rather, they are made up of ions held together by ionic bonds.
Copyright © 2011 Nelson Education Ltd. Chapter 3: Molecular Compounds and Intermolecular Forces 3-2
30. The two main reasons for the formation of hydrogen bonds are: (1) The electronegativity
difference between hydrogen and nitrogen, oxygen, or fluorine atoms is very large. Bonding
electrons are therefore attracted more to a nitrogen, oxygen, or fluorine atom than to a hydrogen
atom. (2) The small size of a hydrogen atom gives it a concentrated positive pole that is strongly
attracted to neighbouring negative poles.
31. Some outdoor clothing is made of fleece that might be manufactured from substances that
come from recycled plastic bottles.
Understanding
32. The wood in a forest could become a non-renewable resource if the forest is not used
sustainably. That is, if the trees are harvested for their wood at a greater rate than new trees can
be grown, they will not be able to replace the trees that are cut down.
33. The strong, very stable bonds in most plastics make plastic products durable so that they have
long, useful lives. However, the products are often so durable that they will not break down in
the environment when discarded, especially if they are made of petroleum-based plastics.
34. You would want to avoid getting a DEET-based insect repellant spray on your clothes
because DEET can damage various fabrics.
35. In a polar covalent bond, the atoms share electrons unequally, giving one atom a partial
positive charge and the other atom a partial negative charge. In a polar molecule, polar covalent
bonds are asymmetrically distributed in three dimensions. The result is that one part, or pole, of
the entire molecule acquires a partial negative charge while the opposite part, or pole, acquires a
partial positive charge.
36. Electrons are in constant motion, making them seem to fill, all at once, a region of space. If
they spend more time in one part of this region than another, the electron density will be greater
there, just as a cloud can be thicker in some places and thinner in others. In a polar covalent
bond, the more electronegative atom pulls the electrons in the bond toward itself, causing the
electrons to spend more time near that atom. As a result, the electron density is greater around
the more electronegative atom.
37. Structure (b) is a better representation of the three-dimensional shape of a water molecule
because a water molecule has a bent shape.
38. (a) In order of decreasing polarity: N–F, H–Br, Cl–Cl
(b) In order of decreasing polarity: As–O, C–N, C–S
39. (a) The most polar bond is N–F. The partial charges are shown: δ+ N–F δ–
(b) The most polar bond is As–O. The partial charges are shown: δ+As–O δ–
Copyright © 2011 Nelson Education Ltd. Chapter 3: Molecular Compounds and Intermolecular Forces 3-3
40. (a) Bromine molecules are non-polar because each has only a single non-polar covalent
bond.
(b) Sulfur dichloride has 2 S–Cl bonds, and the electronegativity difference between sulfur and
chlorine is 0.6, indicating that the bonds are slightly polar. The polar bonds are not
symmetrically distributed in three dimensions, so SCl2 molecules are polar.
(c) Beryllium dichloride has 2 Be‒Cl bonds, and the electronegativity difference between
beryllium and chlorine is 1.6, indicating that the bonds are strongly polar covalent. However, the
bonds are symmetrically distributed in three dimensions, so BeCl2 molecules are non-polar.
(d) Phosphorus trifluoride has 3 P‒F bonds, and the electronegativity difference between
phosphorus and fluorine is 1.0, indicating that the bonds are polar covalent. The polar bonds are
not distributed symmetrically in three dimensions, so PF3 molecules are polar.
(e) Iodine fluoride has a single I‒F bond, and the electronegativity difference between iodine and
fluorine is 1.0, indicating that the bonds are polar covalent. Since there is only one bond in each
molecule, IF molecules are polar.
Copyright © 2011 Nelson Education Ltd. Chapter 3: Molecular Compounds and Intermolecular Forces 3-4
(f) In tetrafluoroethene, C2F4, the carbon–carbon double bond is non-polar. The electronegativity
difference between carbon and fluorine is 1.4, indicating that there are four polar covalent bonds
between the carbon and fluorine atoms. The distribution of these four bonds is symmetrical in
three dimensions, so C2F2 molecules are non-polar.
41. In the solid state, carbon dioxide molecules do not have enough energy to move apart against
the intermolecular forces that hold them in a tightly clustered arrangement. When more energy is
available, however, the molecules eventually break free of the intermolecular forces and enter
the gaseous state, spreading far apart.
42. (a) Force 1 is a polar covalent bond. Force 2 is a dipole–dipole force.
(b) Covalent bonds are stronger than dipole–dipole forces. The supporting evidence is that the
thermal energy required to overcome dipole–dipole forces is less than the thermal energy
required to break covalent bonds. This is seen in the fact that when liquid hydrogen bromide
evaporates due to supplied thermal energy, the molecules separate but remain individually intact.
The thermal energy is sufficient to overcome the dipole–dipole forces between neighbouring
molecules, but it is not sufficient to overcome the covalent bonds within molecules.
43. London dispersion forces exist between all molecules and atoms. London dispersion forces
result from temporary shifts of electrons on one entity toward protons on another entity. Since all
molecules and atoms have electrons and protons, they all exert London forces on one another.
Dipole–dipole forces, on the other hand, can only exist between the partially charged poles of
polar molecules, and hydrogen bonding only occurs between molecules that have hydrogen
atoms bonded to highly electronegative elements such as nitrogen, oxygen, or fluorine.
44. Both London dispersion forces and dipole–dipole forces result from the attraction of a
positive pole on one molecule and the negative pole on another molecule. Dipole–dipole forces
result from the attraction of the permanently charged poles on neighbouring polar molecules.
London forces, on the other hand, result from temporary poles on molecules formed by
momentary shifts of the electron clouds. These temporary poles are short-lived, so London force
attractions are constantly forming and breaking.
45. (a) At room temperature, hydrogen sulfide is a gas, so room temperature must be higher than
the boiling point of hydrogen sulfide. Water, on the other hand, is a liquid at room temperature,
so its boiling point must lie above room temperature. Thus water has a higher boiling point than
hydrogen sulfide.
(b)
Copyright © 2011 Nelson Education Ltd. Chapter 3: Molecular Compounds and Intermolecular Forces 3-5
(c) The molecular shapes of H2O and H2S are the same. The bonds are asymmetrically
distributed in three dimensions in the same manner for each molecule.
(d) The difference in boiling points of water and hydrogen sulfide can be accounted for by the
fact that hydrogen bonds can form between water molecules, but not between hydrogen sulfide
molecules, giving water a much stronger intermolecular attraction than hydrogen sulfide. The
greater degree of intermolecular attraction in water requires more energy to separate the
molecules so that it can become a gas. Thus, water has the higher boiling point.
46. It is important to drain water pipes in unoccupied, unheated homes in the winter because,
with no heating, the temperatures inside the house could be low enough to freeze the water in the
pipes. The expansion of water as it becomes ice could burst the pipes. If temperatures then warm
sufficiently, the ice could melt and water could leak out, flooding the home.
47. Ice is less dense than the water from which it forms. Due to the lower density, ice floats on
liquid water. The layer of ice will remain atop the water and perhaps even insulate the water
below from further freezing.
48. Water is often chosen as a coolant because it has an unusually high specific heat capacity.
This means that water can absorb a relatively large quantity of energy per 1 °C rise in
temperature. Since water remains cooler than other liquids as it absorbs energy, a larger
temperature difference can be maintained between water and an object or system it is cooling.
Thermal energy therefore continues to flow into the water. This makes water a good choice for a
coolant.
49. If a product is to be environmentally harmless from its manufacture to the end of its useful
life, it must require only renewable resources for its production. Its manufacturing process would
require relatively little energy and would be minimally polluting. The product would have a long,
useful life so that the resources needed for its manufacture would not be taxed by the production
of replacements. At the end of its useful life, the product should be biodegradable or recyclable.
50. Products made from recycled materials are generally greener than those made from new
materials because recycling keeps some used materials out of landfill sites, avoids the need to
use new resources (which may or may not be renewable), and generally uses less energy than
using new materials.
Analysis and Application
51. Answers may vary. Sample answer: Petroleum is used as the starting material for a very large
number of important products that include synthetic fibres, plastics, and synthetic rubber. If we
waste petroleum by turning it into gasoline and burning it in the engines of big, low-gas-mileage
vehicles, there will be less petroleum available for making other products. If the supply of
petroleum is exhausted by wasteful consumption of gasoline, we will have to seek new resources
for synthetic clothing fibres and many useful household products.
52. Answers may vary. Students should provide three properties for each item. Sample answers:
(a) The hose for a gasoline pump should be flexible, strong, and not chemically changed by
gasoline or anything in the air. It should retain its qualities over a large temperature range. It
should be flame resistant.
(b) The adhesive for patching the holes in inner tubes and inflatable pool toys should be flexible
so that the bond it creates between the tube/toy and the patch will not break upon flexing. In
addition, the adhesive must be chemically stable so that the bond does not deteriorate over time
and does not weaken the surrounding material. It must have a high enough melting point that it
does not soften and weaken when the temperature rises. It must also be insoluble in water.
Copyright © 2011 Nelson Education Ltd. Chapter 3: Molecular Compounds and Intermolecular Forces 3-6
(c) The fabric of a camping tent must be strong enough not to tear when stretched. It should be
low in density so that the tent is not too heavy. The fabric should also be resistant to deterioration
due to chemical or physical attack by moisture, sunlight, or oxygen. Finally, it should be
waterproof and non-toxic.
53. Answers may vary. Sample answer: If I were asked to develop new scented insect repellants,
I would start my research by looking at molecular compounds. In order for a compound to impart
a scent to the product, the compound must vaporize readily. This means that the forces holding
the particles of the compound together must be relatively weak, because weaker forces would
allow the particles to more readily break free of the solid or liquid and become vapour. An ionic
compound is held together by ionic bonds, which are much stronger than the intermolecular
forces that hold a molecular substance in the liquid or solid state. Thus a molecular compound is
more likely to have an odour.
54. (a) When a thin stream of decane is passed near a negatively charged vinyl strip, the decane
will not be deflected. The electronegativity difference between hydrogen and carbon is 0.4, so
the carbon–hydrogen bonds in decane are only slightly polar. In addition, the bonds are
symmetrically distributed in three dimensions, so decane molecules are non-polar. Decane
molecules, therefore, will not be attracted to a charged vinyl strip, as shown in the diagram
below.
Copyright © 2011 Nelson Education Ltd. Chapter 3: Molecular Compounds and Intermolecular Forces 3-7
(b) When a thin stream of propanal is passed near a negatively charged vinyl strip, the propanal
will be deflected. The carbon–hydrogen bonds in propanal molecules are only slightly polar, as
explained in part (a). The carbon–oxygen bond, however, is more polar, because the
electronegativity difference between carbon and oxygen is 0.8. The bonds in propanal are not
symmetrical in three dimensions, so the molecule is polar, with the oxygen end having a partial
negative charge. The partial charges on the propanal molecules will cause a thin stream of
propanal to be attracted to the negatively charged vinyl strip, as shown in the diagram below.
55. The difference in boiling points between ethanol, 78 °C, and methoxymethane, –24 °C, is
explained as follows: A molecule of ethanol, C2H5OH(l), has a polar covalent bond between the
oxygen atom and a carbon atom. The oxygen–hydrogen bond is also polar. The bond polarities
and the asymmetrical distribution of the bonds in three dimensions cause ethanol molecules to be
polar with a partial negative charge on the oxygen end of the molecule. Similarly, a molecule of
methoxymethane, C2H6O(g), is polar because of polar oxygen–carbon bonds and an
asymmetrical distribution of the bonds in three dimensions. Again, the oxygen end of the
molecule will have a partial negative charge. Since both molecules have similar dipoles, they
will have about the same degree of dipole–dipole attraction. In addition, molecules of both
substances have the same number of protons and electrons (26), so we can expect the London
dispersion forces to be equally strong in them. Hydrogen bonding, however, can occur in ethanol
because its molecules have a hydrogen–oxygen bond, but not in methoxymethane because its
molecules only have carbon–oxygen and carbon–hydrogen bonds. Hydrogen bonding is
generally stronger than the other intermolecular forces, which gives ethanol stronger
intermolecular attractions and a higher boiling point.
Copyright © 2011 Nelson Education Ltd. Chapter 3: Molecular Compounds and Intermolecular Forces 3-8
56. The difference in boiling points between methanol, 65 °C, and butan-1-ol, 118 °C, is
explained as follows: In the molecules of both methanol, CH3OH(l), and butan-1-ol, C4H9OH(l),
the polar covalent bonds between a carbon atom and the oxygen atom and between a hydrogen
atom and the oxygen atom result in a partial negative charge on the oxygen end of the molecule.
The dipole–dipole forces will be similar in both substances. Similarly, hydrogen bonding can
occur between the molecules of each substance, so these forces should be similar in both
methanol and butan-1-ol. However, butan-1-ol molecules have more electrons and protons than
methanol molecules and thus will have stronger London dispersion forces. The stronger London
forces in butan-1-ol account for the higher boiling point of butan-1-ol.
57. Cleaning clothes with liquid carbon dioxide results in energy savings when the clothes are
“dried” in the washing chamber because energy is not required to dry the clothes. Carbon dioxide
molecules are non-polar and have very weak intermolecular forces. As a result, the thermal
energy available at room temperature is more than enough to rapidly vaporize liquid carbon
dioxide in the washed clothes. The clothes “dry” all on their own and do not need to be placed in
a dryer. Not using a dryer saves energy.
58. (a) The boiling point of hydrogen fluoride, HF, is higher than the boiling points of the other
hydrogen halides, HCl, HBr, and HI, because hydrogen fluoride molecules can form hydrogen
bonds to one another, whereas the other hydrogen halide molecules cannot. The greater strength
of hydrogen bonds compared to dipole–dipole forces and London dispersion forces accounts for
the higher boiling point of hydrogen fluoride.
(b) The boiling points of hydrogen halides increase as one moves down the family from
hydrogen chloride to hydrogen bromide to hydrogen iodide. This indicates that hydrogen
chloride has the weakest intermolecular forces and hydrogen iodide has the strongest. The reason
cannot be dipole–dipole forces, because the most polar bond of H–Cl, H–Br, and H–I is H–Cl, so
hydrogen chloride molecules should have the strongest dipole–dipole forces. London dispersion
forces, on the other hand, should be strongest for hydrogen iodide because its molecules have the
greatest number of electrons and protons. The number of electrons in each molecule also
explains why London forces are weakest for hydrogen chloride. Thus, the boiling point rises
from hydrogen chloride to hydrogen iodide because the strength of the London dispersion forces
increases.
59. The trend in boiling points for hexane, C6H14, heptane, C7H16, and octane, C8H18, will be to
increase as the size of the molecule increases. All of the substances have molecules with bonds
that are symmetrically distributed in three dimensions, so all three substances are non-polar. This
means that London dispersion forces are the only forces of attraction between the molecules of
each substance. As the number of protons and electrons in the molecules of a molecular
substance increases, the strength of the London dispersion forces between the molecules
increases, resulting in a higher melting and boiling point. Octane has the greatest number of
protons and electrons in its molecules, and hexane the least, so the London forces are strongest in
octane and weakest in hexane. Thus, the boiling points will increase from hexane to heptane to
octane.
Copyright © 2011 Nelson Education Ltd. Chapter 3: Molecular Compounds and Intermolecular Forces 3-9
60. Placing a drop of detergent onto the water next to a floating plastic clip will cause the clip to
surge forward because the detergent reduces the surface tension of the water. The surface tension
in water results from intermolecular forces, principally hydrogen bonding, pulling molecules
toward each other at the surface. The inward pull causes the surface to resist being spread apart,
almost like a tight sheet of rubber resists being stretched further. Before the detergent is dropped
in the hole of the bread clip, the intermolecular forces pull equally in all directions. After the
detergent is dropped in the hole, intermolecular forces are reduced at the back of the clip. This is
because detergent molecules have a polar end and a non-polar end. Water molecules are attracted
to the polar ends of the detergent molecules and this interferes with hydrogen bonding between
water molecules. The result is a net pull that moves the water under the front of the bread clip
forward, thus causing the clip to move forward as well.
61. Adding soap to water affects the ability of water to form beads on a horizontal surface
because the soap reduces the surface tension of the water. Water forms beads on a smooth
surface because of its strong intermolecular attraction, which is primarily due to hydrogen bonds.
This causes water molecules to be attracted to one another rather than to the air above it and thus
to form a shape with a minimum surface area. A spherical shape has the least surface area, so
beads of water are like little spheres resting on a surface. The forces that form these spheres are
strong enough to prevent gravity from flattening them. If soap molecules reduce the strength of
the intermolecular forces in water, the water molecules will no longer be able to pull hard
enough on one another to form beads. Instead, gravity will pull the water down into a thin layer.
62. Water that penetrates asphalt can be a problem when temperatures fall below freezing
because the water will freeze. Upon freezing, the water will expand as the liquid turns to ice. The
force exerted by the expansion can be strong enough to break the asphalt apart and create cracks
and potholes, especially after many freeze–thaw cycles.
63. (a) Given: Vwater = 100 cm 3
dwater = 1.00 g/cm 3
dice = dwater – (9 % of dwater )
Required: Vice
m
m
, so V = . Since 1 cm3 of water has a mass of 1 g,
V
d
3
the mass, m, of 100 cm of water is 100 g. The water has a mass of 100 g regardless of whether it
is liquid or solid.
Solution:
Step 1. Calculate the density of the ice.
dice = dwater – (9 % of dwater )
Analysis: The formula for density is d =
= 1.00 g/cm 3 – 1.00 g/cm 3 (0.09)
= 1.00 g/cm 3 – 0.09 g/cm 3
dice = 0.91 g/cm 3
Copyright © 2011 Nelson Education Ltd. Chapter 3: Molecular Compounds and Intermolecular Forces 3-10
Step 2. Calculate the volume of 100 g of ice.
m
Vice =
dice
! 1 cm 3 $
= 100 g #
&
" 0.91 g %
Vice = 110 cm 3
Statement: The volume of the ice resulting when 100 cm3 of water freezes is 110 cm3.
(b) My answer to (a) shows that the volume of the ice is greater than the volume of the water.
This might affect water pipes during the winter if water has been left in the pipes, because as the
water freezes and expands when the temperature drops below freezing, the resulting pressure on
the pipes might cause them to crack.
64. Graph A best represents how the density of water varies with temperature. It shows that ice is
less dense than liquid water. Graphs B and C are inconsistent with the fact that ice is less dense
than liquid water. Graph A also shows both ice and liquid water becoming less dense as
temperature increases, which would be expected.
65. Answers may vary. Sample answer: It really does not matter whether or not governments
give tax breaks or subsidies to manufacturers of bioplastics to help offset production costs and
allow them to sell their plastics at a lower, more competitive price. I might then be able to buy
bioplastics products at about the same price as traditional plastic products, but I will have to pay
more taxes to cover the loss of taxes collected from the bioplastics manufacturers or the cost of
subsidies given to them. More taxes for me is not any different than paying higher prices for
bioplastics products when there are no tax breaks or subsidies. Consequently, tax breaks and
subsidies are not an effective way to increase the use of bioplastics. What really matters is the
health of the environment. I am willing to pay more for products made with bioplastics simply
because I know that it is the right thing to do for our future.
Evaluation
66. Answers may vary. Sample answer: To evaluate which of several reusable water bottles is
best, I would first perform strength tests to see how durable the bottles are. One way to do this
would be to drop the bottles repeatedly from a standard height and observe how long each lasts
before cracking or breaking. I would also see which bottle was the least prone to leaking. For this
test, I would screw the lid on with a standard force, place the bottle in a container, shake the
container in a standardized manner, and observe how much, if any, water leaked out of the bottle.
Testing the stability of the bottle when opened and standing on a table would be important
because bottles that are easily knocked over are a nuisance. For this test, I would place a standard
amount of water in an open bottle, place the bottle on a tabletop, bump the table with a standard
force, and observe which bottles were least likely to be knocked over. Finally, I would run the
bottles through many dishwasher cycles to see which showed the least evidence of deterioration
upon cleaning. The best bottles would show the least deterioration and would thus have the
longest useful lives.
Copyright © 2011 Nelson Education Ltd. Chapter 3: Molecular Compounds and Intermolecular Forces 3-11
67. For a solvent to be suitable for use as a liquid in the synthesis reaction, the solvent must be
liquid, not a gas, at 60 °C. This rules out dichloromethane and silicon tetrachloride, as both boil
below 60 °C. Secondly, the solvent must be non-polar. Non-polar molecules either have nonpolar covalent bonds or a symmetrical distribution of bonds in three dimensions. Acetonitrile and
dimethyl sulfoxide have molecules with polar covalent bonds, and the bonds are asymmetrically
distributed in three dimensions. This rules out these two liquids. Carbon tetrachloride has polar
covalent bonds, but the bonds are symmetrically distributed in three dimensions. Accordingly,
this compound is non-polar as desired. The chemist should use carbon tetrachloride because it is
a liquid at 60 °C and is non-polar.
68. (a) The degree to which the molecules in the liquids in Table 3 have charged ends is
evaluated as follows: To have charged ends, the liquid must be a polar substance. The bonds in
pentane molecules and in carbon disulfide molecules are symmetrically distributed in three
dimensions, so these molecules are non-polar. Methanamide and propanone molecules both have
polar covalent bonds. The double carbon–oxygen bond in each molecule has an electronegativity
difference of 0.8, indicating polar covalent bonding. Also, the bonds in these two molecules are
asymmetrically distributed in three dimensions. Thus, these molecules are polar and have
partially charged ends.
(b) The researcher should test methanamide and propanone as possible insulators for capacitors.
The insulator works best when its molecules have charged ends, which means they are polar. Of
the four possible insulators, methanamide and propanone are the most suitable liquids for testing
because they are polar molecules. Pentane and carbon disulfide would not make good insulators
because their molecules are non-polar.
69. (a) PLA plastic alone would not be a good choice as a material with which to build computer
cases because it is quite flammable. Computer cases, particularly laptop cases, can get very hot,
so a computer case made of PLA would pose a fire hazard.
(b) A PLA plastic that incorporates metal hydroxides might be more suitable for the computer
cases. Metal hydroxides incorporated into the PLA plastic would absorb thermal energy and thus
act as a fire retardant. This would make the plastic much more flame-resistant.
70. Answers may vary. Sample answer: If the world were to substitute bioplastics for petroleumbased plastics on a large scale, one problem that might arise is food shortages, particularly in
regions that commonly experience food shortages, as food crops would have to be diverted to the
manufacturing of the bioplastics. Further research topics within this problem include the total
area of land currently being used worldwide for agricultural purposes and how much other land
is available that could potentially be used for the raising of crops. If not much land is available
for the expansion of agriculture, the diversion of crops to the manufacturing of bioplastics could
threaten food supplies in a world already experiencing serious food shortages. On the other hand,
if a great deal of new land could be put into use for the raising of crops, the sale of such crops
could boost economies without threatening the world’s food supply. In such a scenario, raising
crops for bioplastics should be encouraged. However, I would also have to find out about the
profitability of selling crops for use in making bioplastics. If crops will fetch a better price when
sold for plastics as opposed to being sold for food, farmers might opt for the more profitable
option, even if that means less food for hungry people. To protect starving people from the loss
of a food supply, governments might have to subsidize farmers who grow crops for food.
Copyright © 2011 Nelson Education Ltd. Chapter 3: Molecular Compounds and Intermolecular Forces 3-12
Reflect on Your Learning
71. Answers may vary. Sample answer: After reading this chapter, I am more likely to buy
upcycled products. The production of upcycled products provides jobs without requiring a great
deal of consumption of natural resources. Upcycled products might not seem stylish or fancy
enough to some people, but I would rather be environmentally stylish than fashionably stylish.
72. Answers may vary. Sample answer: Considering what I have learned in this chapter about
insect repellants, I am no less likely to use an insect repellant when outdoors. I do not want to
risk getting West Nile virus from a mosquito bite, and I can choose insect repellants that do not
contain DEET. If only repellants with DEET were available, I would still use insect repellant. I
know that DEET in insect repellents may be the cause of a small number of seizures in adults,
and that DEET-based repellents should not be used on infants or by pregnant or breastfeeding
women, or on children in concentrations greater than 10 %. But millions of people have used
DEET-containing insect repellants without adverse health consequences, so I doubt I would be at
risk. I would try to use insect repellents with lower concentrations of DEET and cover up with
clothing as much as possible rather than slathering on repellent. I would also be very careful not
to get DEET in my mouth when applying insect repellent to my face.
73. Answers may vary. Sample answer: This chapter has helped me see that the marketing
strategy used by electronic retailers of promoting new models and features to make older models
seem out of date is bad for the environment. Many electronics contain toxic chemicals that enter
the food chain and bioaccumulate when they get thrown out. These products also use nonrenewable resources and may add to landfills when they are discarded. On the other hand,
electronic items can be recycled and new models usually offer upgraded features that provide
greater convenience or effectiveness. I think the best approach is to not run to the store the
minute a fancier cell phone or music player is released, but to enjoy your current model for a
significant time, and then buy an upgraded model second-hand, which will save you money and
be better for the environment.
Research
74. Single-stream recycling is based on separating the items and materials from a mixture of all
types of recyclables into groups that are suitable for shipment to an appropriate processing
operation. Sorting is done both by hand and by machine in ingenious ways. Magnets are used to
pull out metals that contain iron. Jets of air are used to separate paper from plastic. Single-stream
recycling is very convenient for the consumer because he or she does not have to pre-sort
recyclables for pickup. Waste-disposal costs can be higher, however, because of the machinery
and employees needed at the receiving facility. Students’ reports should focus on the Peel
Integrated Waste Management Facility and include flow charts or diagrams that describe the
step-by-step sequence of separations in this facility.
75. Students will research polylactic acid, PLA, and produce a pamphlet or audiovisual
presentation that will include the following information:
(a) Answers may vary. Sample answer: PLA, polylactic acid, is a polymer of lactic acid. This
means that many molecules of lactic acid (lactic acid monomers) are joined together into very
long molecules. The long molecules are the polymers. The lactic acid monomers cannot be
polymerized directly because this reaction produces water that prevents further polymerization
reactions from happening. This problem is avoided by converting the lactic acid to a ring
structure that is then converted to the polymer.
Copyright © 2011 Nelson Education Ltd. Chapter 3: Molecular Compounds and Intermolecular Forces 3-13
(b) Answers may vary. Sample answer: PLA offers the obvious green benefit of being
compostable and thus, if composted, will not clutter landfills like traditional plastics. However,
PLA is not recyclable. Single-stream waste sorting operations regard PLA as a nuisance because
it must be sorted out from other plastics and disposed of separately. Also, large amounts of PLA
can make compost wetter and more acidic, making it difficult to supply enough oxygen to the
compost pile.
76. Students’ reports on the various phases of ice should explain that water freezes at a
temperature below 0 °C under a pressure higher than 100 kPa. Ice may be any one of the 15
crystalline phases of water, depending on pressure and temperature. The density of ice varies
with pressure and the density variations are reflected in the lattice structures. Almost all ice in
the biosphere has a hexagonal crystal structure. Students should include a diagram of the
conditions under which the various phases form similar to the graph below, and also provide
diagrams of the various crystal lattice structures similar to those in the table below.
Lattice Structures of the 15 Phases of Ice
Crystal
lattice
structures
hexagonal
rhombohedral
Ice phases
Ih
(almost all
ice in the
biosphere)
II and IV
tetragonal
III, VI,
VIII, IX,
and XII
monoclinic
V and XIII
cubic
Ic, VII, and X
orthorhombic
XI and XIV
Copyright © 2011 Nelson Education Ltd. Chapter 3: Molecular Compounds and Intermolecular Forces 3-14
77. Bisphenol A, or BPA, may be linked to a number of serious health concerns, such as
neurological problems, obesity, cancer, and reproductive system anomalies. Its main use has
been in the manufacturing of polycarbonate plastics and epoxy resins. Data show that BPA can
leach out of plastics in drinking bottles and other products and enter the body or the
environment. One of the most serious concerns is the use of BPA in baby bottles. Health Canada
declared BPA to be a toxic substance in 2010. Students’ reports should include information
about the historical uses of BPA, the possible health risks it poses, and the arguments against and
for its use.
Copyright © 2011 Nelson Education Ltd. Chapter 3: Molecular Compounds and Intermolecular Forces 3-15