Extension 12. (a)

Extension 12. (a)

(b) Animal hides decompose quickly unless they are cured to remove the water from the skin. The hide is first soaked in water to remove water-soluble substances, and hair is removed by soaking in a mixture of lime and water, followed by an enzyme mixture. The hair and any remaining tissue are removed by machine and the hide is washed and treated with tannic acid. The tannic acid displaces water from the spaces between the protein fibres of the hide, allowing the fibres to cement together to form a strong, water-resistant leather.

13. (a) First molecule: one cis and two trans Second molecule: two cis and two trans

(b) Transfats increase the level of low-density lipoprotein (LDL) or “bad” cholesterol in the bloodstream, which contributes to clogging of the arteries. As arteries clog, the risk of stroke and heart attack increases.

10.5 POLYMERIZATION REACTIONS—MONOMERS AND POLYMERS Web Activity: Web Quest—Teflon: Healthy or Hazardous?

(Page 448)

[Students’ presentations may cover some of the following material.]

Production of Teflon

To produce polytetrafluoroethylene (PTFE or Teflon®), the manufacturer first needs a steady supply of tetrafluoroethylene (TFE). To produce the required TFE, three main ingredients, fluorspar, hydrofluoric acid, and chloroform are combined in a reaction chamber and heated to between 590 ˚C and 900 ˚C. The gas produced is cooled and then distilled to remove impurities.

A possible sequence of reactions is:

CaF

(s) + H

SO

(aq) o CaSO

(s) + 2 HF(aq)

CH

(g) + 3 Cl

(g) o CHCl

(g) + 3 HCl(g)

CHCl

(g) + 2 HF(g) o CHClF

(g) + 2 HCl(g)

2 CHClF

(g) o CF

CF

(g) + 2 HCl(g)

One method of producing PTFE from the TFE is by suspension polymerization. In this process, a reaction chamber is filled with purified water and a reaction agent or initiator, which will set off the reaction of the PTFE. Liquid TFE is then piped into the reaction chamber. When it contacts the initiator, it starts the polymerization process. While this is occurring, the reaction chamber is mechanically shaken and the chamber is cooled by the flow of cold water or coolant through the walls of the chamber. When enough TFE has reacted (by mass), the water is drained from the container and the PTFE is removed. It is then dried, fed into a mill, and pulverized into a powder.

Once in powder form, manufacturers typically agglomerate the PTFE into pellets, which have a consistent size and shape. In this form, the PTFE can be more easily moulded into parts by means of a variety of techniques.

The dispersion polymerization method of producing PTFE agitates the chamber lightly instead of shaking it vigorously. This allows the PTFE to form into tiny beads. Added chemicals cause the beads to settle and change into a milky substance, which is called a PTFE dispersion.

As a liquid, the PTFE is much easier to manipulate for use in fabric finishes and for coating metals.

To coat cookware with PTFE, the item must be made of aluminium or an aluminium alloy and the surface must be prepared to receive the PTFE. First, the item is washed with detergent and then rinsed with water. The item is then etched with a solution of hydrochloric acid to roughen the surface, is rinsed with distilled water and nitric acid, and is then washed again and rinsed again with distilled water. At this point the item is coated with a primer (a trade secret) that helps the PTFE bond to it. A number of layers of PTFE are then applied, and cured onto the cookware. After the cookware has been put through a cooling process, it is ready for final assembly and packaging.

The summary for the addition reaction of TFE to produce PTFE is shown on page 447 of Chapter 10.

Concerns About Teflon

DuPont has spent considerable effort defending both its Teflon brand name and the processes involved in its manufacture. One common misconception is that Teflon itself is

dangerous, although there seems to be no scientific basis for that idea. However, there is growing evidence that chemicals involved in the manufacture of Teflon® and released during the

decomposition of Teflon are dangerous.

One such chemical is perfluorooctanoic acid (PFOA or C-8). PFOA is used in the manufacturing of Teflon, and testing by the FDA has shown that under normal usage Teflon coatings do not contain or emit measurable amounts of PFOA. PFOA is a concern because it is highly resistant to breaking down and accumulates in the food chain. Traces of the PFOA family of chemicals can be found in the blood of virtually everyone in North America, and as of yet there are no studies that definitively answer how this has happened. DuPont has been fined by the Environmental Protection Agency (EPA) in the United States for failing to disclose how toxic PFOA is, but DuPont has admitted no liability after settling the issue. As of February 2006, the EPA’s Science Advisory Board has voted to approve a recommendation that PFOA be considered a likely carcinogen.

DuPont also claims that evaluation of human health and toxicology studies shows that PFOA does not pose a health or cancer risk to humans, and that there are no significant risks in exposure to PFOA from using Teflon.

As regards overheating Teflon during the cooking process, there are conflicting opinions.

DuPont claims that the maximum recommended temperature for Teflon cookware is 500 ˚F

(260 ˚C), and that temperatures above that are not obtained in normal cooking processes. DuPont

also claims that significant breakdown of Teflon occurs only at temperatures of 660 ˚F (349 ˚C),

which is well above the smoke point for fats or butter. DuPont suggests that only leaving

cookware dry and unattended while under intense heat would cause any issue, and no matter what kind of cookware it is, that should never be done.

As well, other groups, such as the American Heart Association and the National Stroke Association, claim that cooking with Teflon is still a safer and healthier alternative as you can use less fat (with lower health risks of stroke and heart disease) and improve the natural taste of foods. Beyond any health risks, it is suggested that since most kitchen fires are caused by grease and oil igniting, using non-stick cookware lessens the risk of a fire in the kitchen.

Groups concerned about Teflon argue that there is a significant risk of overheating the cookware and producing toxic gases in the home. Polymer fume fever (or Teflon flu) is an acknowledged issue with overheating the coating. Symptoms include headache, chills, cough, fever, and shortness of breath, which often are similar to symptoms of the common flu virus.

There are also documented cases of birds being killed when a non-stick pan is overheated in a kitchen. Birds and small animals seem to be especially sensitive to the gases produced, and even DuPont has issued a warning about this issue.

Pros and Cons of Various Types of Cookware

There are many pros and cons for each type of cookware. Sample answers are listed here.

Ɣ Teflon Pro: cookware is now relatively inexpensive, very easy to clean, light, and allows less oil to be used in frying and cooking.

Ɣ Teflon Con: can produce toxic gases when heated improperly, can be scratched over time, wears out in a few years of use, and may not have good heat retention (depending on the mass).

Ɣ Steel Pro: heavier cookware has a more even heat once brought to temperature, is much longer lasting that most cookware, and has low upkeep.

Ɣ Steel Con: generally quite expensive, containers are heavy, needs non-stick spray or oil to keep food from sticking, and not as good at conducting heat.

Ɣ Other types of cookware that could be discussed include: glass, aluminium, steel clad, copper, ceramic, and cast iron.

[Students are also expected to take a position on whether Teflon or one of its alternatives is the better option for cookware.]

Practice (Page 448)

(Butenes in #1 and #7 should have the location numbers between prefix and ending.) 1. (a) polymer of but-1-ene

(b) polymer of vinyl fluoride

(c) polymer of 1-chloro-1,2,2-trifluoroethene

(d) The presence of highly electronegative Cl and F atoms makes the polymer more polar and thus not very soluble in nonpolar organic solvents. The absence of C-H bonds and the presence of strong C-F and C-Cl bonds makes this polymer unreactive and therefore resistant to heating. The lack of bulky side chains and uniform structure makes this polymer rigid.

2.

3. (a) but-2-ene

(b) 1-chloro-1,2-difluoropropene

4. The monomer must have a double or triple bond to form an addition polymer.

5.

6. (a) Typical properties of plastic are that it is flexible, light in weight, electrically

nonconductive, and able to be molded into different shapes. Plastics will also soften when heated.

(b) Within long polymer molecules you would expect to find intramolecular covalent bonds.

Between polymer molecules there would be intermolecular forces, such as London and dipole–dipole forces.

(c) Intramolecular bonding: the prevalence of single, rather than multiple, carbon–carbon bonds makes plastics strong and chemically unreactive.

Intermolecular bonding: the intermolecular attractions hold the molecules together but are weaker so that the molecules can move to produce both flexibility and the ability to be molded into different shapes.

7. (a) (b) (c)

8.

SPI resin code

Type of products Properties Accepted by

municipal recycling organization?

Accepted by other recycling

organization?

1

(PETE) bottles for

carbonated drinks, containers for peanut butter and salad dressings

clear; strong; barrier to gas

and moisture; heat resistant Yes No

2 (HDPE)

milk, water, juice bottles, grocery bags

rigid; strong; resistant to chemicals and moisture

Yes No

3

(V) plastic siding, water

pipes, syringes strong; easily blended;

resistant to grease, oil, and other chemicals; clear or coloured

No Building materials may be

recycled.

4

(LDPE) dry-cleaning and grocery bags, flexible containers and lids

strong; flexible; resistant to

moisture No No

5

(PP) ketchup bottles, margarine containers

strong; resistant to grease, oils, and other chemicals;

resistant to heat and moisture

Yes No

6 (PS)

meat trays, plastic knives, spoons, forks, CD cases

transparent; “expanded” form – good insulator

Yes No

Web Activity: Case Study—Recycling Plastics (Page 449)

Procedure for processing recycled plastic:

1. Inspection

2. Chopping, washing and separation by flotation

3. Drying, melting, filtering and extrusion into fine strands 4. Pelletizing, if required

5. Ship to plastic reprocessor to manufacturer final products Pro Perspectives

Ɣ Technological: Plastic bags are one of the most efficient and innovative means to transport items from store to home. They are strong, and lightweight.

Ɣ Economic: Plastic items are inexpensive.

Con Perspectives

Ɣ Ecological: Plastic bags and other items often end up in the environment, are nonbiodegradable, and have been known to harm fish.

Paper bags can be made from renewable resources and more easily recycled. Plastic bags are made from nonrenewable fossil fuels.

There are health concerns about the use of plastics in microwaves, food wraps, and other plastic items.

Ɣ Economic: Plastic producers pay a fee per kilogram to support municipal recycling, and this fee is passed on to consumers.

Practice (Page 451)

9. Saturated lipids have more hydrogen atoms than unsaturated lipids with the same number of

carbon atoms. As the number of hydrogen atoms increases, the number of electrons increases,

and therefore so do the London forces. Since the saturated lipids have stronger London

forces, their melting points will correspondingly be higher. (The shapes of the molecules are

also a factor.)

10.

11.

Practice (Page 452) 12.

13. To form a polyester, a dicarboxylic acid (a carboxyl group at each end of the molecule) and a diol (a hydroxyl group at each end of the molecule) are needed.

14. The reactions to form fats and those to form polyesters are similar in that both have alcohol and carboxylic acid groups joining together to produce a larger molecule and water. The reactions are different in that polyesters can be made up of large numbers of dicarboxylic acid and diol monomers reacting, while fats are made up of only three acid and alcohol molecules reacting.

Web Activity: Simulation—Molecular Modelling (Page 452)

[No written response is required for this activity.]

Investigation 10.5: Preparing Nylon 6,10 (Demonstration) (Pages 453, 464)

Purpose

The purpose of this demonstration is to use your knowledge of condensation polymerization to explain the formation of a nylon polymer.

Problem

How does the combination of sebacoyl chloride and 1,6-diaminohexane form the polymer known as nylon 6,10?

Prediction

Evidence

The 1,6-diaminohexane is a clear, colourless solution with a slightly pungent odour. The sebacoyl chloride is also a clear, colourless solution, with a pungent odour.

When the sebacoyl chloride solution was poured onto the 1,6-diaminohexane solution, the two solutions did not mix and a cloudy layer appeared. When forceps were placed into the container, a long white strand was pulled from the interface of the two liquids.

Practice (Page 455)

15. A polyamide is formed by a condensation polymerization reaction.

16. An example of a natural condensation polymer is a protein. An example of a synthetic condensation polymer is nylon 6,6.

17. Repeating unit:

Explore an Issue: Natural or Artificial Polymers?

(Pages 455–456) Issue

Do cloth diapers pose less of a threat to the environment than disposable diapers?

Resolution

Consumers should return to using cloth diapers in order to protect the environment.

Evidence

Pro Perspectives

Ɣ Ecological: Disposable diapers release chemicals called volatile organic compounds,

including toluene, ethylbenzene, and xylene. All these cause environmental damage and may leak from landfills when disposed of.

Disposable diapers use 1.3 million tons of wood pulp (a quarter million trees) each year, along with plastics, which are made from petroleum resources.

It is estimated that washing cloth diapers at home uses the same amount of water as flushing the toilet five to six times each day. This is similar to the normal usage of water by children once they are potty trained. Diaper services, which do high-volume business, are even more efficient.

The materials in a disposable diaper are generally not biodegradable. Even if a diaper contained biodegradable parts, the lack of oxygen and water would slow the decomposition considerably.

Canadians are dumping around 2 billion diapers into landfills every year, which equals about 300 000 T of diapers.

Proper use of disposable diapers involves disposing of fecal matter into the toilet before throwing out the diaper. However, most people never do that. The smell and bacteria can create public health hazards. Also; fecal matter carries live viruses that could be released into the environment through leaking landfills.

Cloth diapers can be used between 100 and 150 times, which lowers their environmental impact per diaper, compared to disposable diapers.

Babies are more susceptible to the toxic effects of air pollutants, such as those emitted

from disposable diapers, because they breathe more air per kilogram of body weight than

adults do.

Cloth diapers “breathe” much better than disposable diapers, keeping babies’ skin healthier. The incidence of diaper rash at any one time is around 7% for babies diapered solely in cloth diapers, but 13% for those in disposable diapers.

Ɣ Economic: Due to the absorbing power of artificial polymers, it is recommended that a baby’s diaper be changed every 2–3 h. This is very costly for parents.

Cloth diapers cost approximately $35 per month per child, while disposables cost approximately $50 per month per child.

Ɣ Social: Leaving a disposable diaper on a baby too long can cause diaper rash, which can make babies cranky and cause undue tension in the household.

Ɣ Legal: It is illegal to dump human waste into landfills, though this is ignored for the use of diapers at this time.

Ɣ Technological: The polymethylacrylate absorber is so efficient at pulling in moisture that often babies seem unaware when they are wet.

Ɣ Scientific: Research has shown that mice exposed to volatile chemicals emitted from

disposable diapers were more likely to experience irritation of the airways than mice exposed to emissions from cloth diapers.

Con Perspectives

Ɣ Ecological: The production and cleaning of cloth diapers require more energy and water and generate more water pollution than the production of disposable diapers.

The soaps used in cleaning cloth diapers may contain phosphates, which are damaging to the environment.

Pesticide usage on cotton crops is greater than for any other crop in the United States.

Since cloth diapers are made from cotton, this usage of pesticides would increase with increased use of cloth diapers.

Ɣ Economic: Cloth diapers are initially more costly to purchase, and often require support clothing such as plastic coverings to protect from leaks.

Cloth diapers require washing, cause extra wear and tear on washing machines, use up hot water, and use costly detergents.

Ɣ Social: Disposable diapers are much more convenient for busy parents. It is difficult to deal with carrying around dirty cloth diapers while traveling or away from home.

Washing cloth diapers entails a lot of work, which many parents are not interested in.

Ɣ Technological: Cloth diapers tend to leak more, and require use of rubber coverings to stop leakage.

Ɣ Political: Politicians do not like getting involved in issues of consumer choice, so there is very little chance for legislation to force the use of cloth diapers.

Ɣ Scientific: New biodegradable diapers, which are a combination of cellulose and synthetic polymers, are being researched and developed. Biodegradable diapers show promise in being able to break down in oxygen and water-poor landfills.

Analysis

Despite the ease of use of disposable diapers, with the large numbers of environmentally friendly soaps available, there is an overwhelming amount of evidence to support the resolution that consumers should return to using cloth diapers in order to protect the environment. However, convenience is more important than ever in society, so the situation is unlikely to change.

Evaluation

The design is deemed adequate because it allowed for the collection of sufficient background

information to reach a consensus on the resolution within the group. However, the design could

be improved by creating a detailed survey and sampling many families with small children.

Mini Investigation: Starch and Cellulose (Page 457)

[No written response is required for this activity.]

Practice (Page 458)

18. Both contain hydroxyl and COC (ether) groups.

19. Starch is used for energy storage. The orientation of the glucose–glucose linkages favours intra-chain hydrogen bonds between hydroxyl groups and results in a helical structure. These chains are sufficiently small to make these polysaccharides somewhat soluble in water and easily transported in the organism.

Cellulose is used for cell structure and strength in plants. The orientation of the glucose–

glucose linkages favours inter-chain hydrogen bonds between hydroxyl groups, which results in a linear structure. These inter-chain links produce a strong, inflexible structure of layered sheets of cellulose, that is insoluble in water and ideal for its function.

20. (a) Sugars: monosaccharides or disaccharides; readily soluble in water.

Starch: polymers of glucose; slightly soluble in water; requires specific enzymes to be broken down into glucose.

(b) Starch: helical polymer chains of glucose; slightly soluble in water; flexible structure allows ready transport throughout the organism.

Cellulose: linear polymer chains with inter-chain hydrogen bonding; rigid and insoluble in water; requires specific enzymes to be broken down into glucose.

21. Carbohydrates have a ring stucture where one of the atoms in the ring is an oxygen atom.

Attached to the carbons in the ring are hydrogen atoms and hydroxyl groups. The general formula is C

(H

O)

.

22. Molecules of sugars have many hydroxyl groups that are capable of hydrogen bonding with other molecules, resulting in high melting points. The intermolecular attractions in

hydrocarbons are mainly the weaker Van der Waals forces.

23. Comparing glucose, starch, and cellulose, glucose is the most soluble in water, starch can be fairly soluble, and cellulose is insoluble. Glucose is highly soluble in water because it is polar and has hydrogen bonding due to its hydroxyl groups. In starch, the glucose monomers are at angles that lead to a helical structure, which is maintained by the hydroxyl groups within the chains themselves. These chains are small enough to be slightly soluble in water. In cellulose, the glucose monomers make long linear polymer chains, which can form layers with other chains due to hydrogen bonding. These long sheets of cellulose are too large to be soluble in water.

Web Activity: Case Study—Cellulose Acetate (Page 458)

1. Typical properties of cellulose acetate polymers include toughness, a deep gloss, high transparency, and a “natural” feel.

2. The major technological applications of cellulose acetates include textiles and fibres, frames for glasses, tools, and film media. Other applications include wound dressings, personal hygiene products, absorbent cloths, specialty papers and filter media.

3. A natural products chemist researches substances that occur naturally.

Section 10.5 Questions (Page 460)

1.

2.

3. [Ideally, students should use computer models where possible to view these molecules. These structures are quite difficult to construct with a physical molecular model kit.]

(a) (b)

(c) (d)

(e) (f)

4. Polyethylene is beneficial because it can be low density (flexible but not strong) or high density (rigid but strong). It can be used at a range of temperatures and is chemically inert. It is used in shopping bags, sandwich bags, plumbing pipes, and wire insulation. These

products, however, are not biodegradable.

An alternative to using standard polyethylene shopping bags would be to use

biodegradable polyethylene bags. These bags have a catalyst added to the polyethylene,

which, along with heat and/or light, degrades the polymer. Microorganisms in the soil can

continue the breakdown of the plastic.

5. Pro Perspectives

Ɣ Scientific: Scientific research is producing a better understanding of molecular structure and properties which will eventually lead to new synthetic materials with better

properties.

Ɣ Technological: We need a continuing supply of petrochemicals to ensure enough feedstock for the ongoing development of new polymers. Also, natural polymers do not have the range of properties to replace synthetic polymers in many technological products and processes.

Ɣ Social: Society has become very dependent on the many products that are made using a variety of polymers from petrochemical feedstock.

Con Perspectives

Ɣ Ecological: We should make more use of natural polymers from renewable resources that do less harm to the environment in their production and disposal.

Ɣ Political: Unless governments enact more legislation, and provide regulations and enforcement, recycling will continue to be haphazard.

6. Advantages: controlled degree of rigidity or flexibility, water-resistant and thus dries readily, durable.

Drawbacks: made from nonrenewable resources, not biodegradable.

7.

8. (a) Natural product: pasta (carbohydrate) Synthetic polymer analog: cellulose polymer (b) Natural product: meat (protein) Synthetic polymer analog: nylon

(c) Natural product: butter (lipid) Synthetic polymer analog: polyester

9. (a) An ideal polymer would be able to absorb sufficient water to sustain a plant for several weeks and absorb nutrients dissolved in water. It would not be harmful to plants and could be tailored to specific types of application (houseplants, outdoor plants). Also, it would degrade after several months into harmless products and would be inexpensive.

(b) Test for absorption: place samples of equal mass of each polymer in equal excess volumes of water and water with dissolved nutrients, and determine the mass of liquid absorbed. Test for release of liquid: mix equal swelled mass of each polymer with equal masses of a variety of soil types, and measure the moisture content over a test period.

Examine the soil and polymer mixture samples at selected time intervals, and test for pH.

Store mixture samples over several months and determine the amount of degradation. An appropriate test period would be two weeks.

(Sample answer:) Test A

polymer mass of water

added (g) mass of water

added (g) mass of polymer + adsorbed water (g)

polymer A 50.0 100.0 70.0

polymer B 50.0 100.0 80.0

Test B

polymer mass of nutrient solution absorbed (g)

% change in concentration of nutrients in excess solution

polymer A 70.0 g + 10

polymer B 80.0 g 0

Test C

polymer mass before

degradation (g) mass after degradation

(8 weeks) (g) PH

polymer A 50.0 g 25.0 5.5

polymer B 50.0 g 40.0 6.5

Analysis: Polymer A absorbs less fluid than polymer B, and does not absorb nutrients as well as polymer B; polymer A also degrades to produce acidic substances. Polymer B allows all nutrients to be absorbed but does not degrade as quickly as polymer A.

10. Ɣ The term “natural” is used to describe products made by plants or animals, such as natural fruit juice. Some molecules made by plants are synthesized in laboratories, e.g., vitamin C; others are made by plants but are treated chemically, e.g., decaffeinated coffee, which is treated with chemicals to remove caffeine. It is difficult to use the term

“natural” with any accuracy because many natural products undergo some treatment during growing or processing.

Ɣ The term “organic” to describe some produce in supermarkets indicates that the item is grown without use of “chemical” substances such as synthetic fertilizers, antibiotics, etc.

In scientific terminology, all plants and animals, and thus most foods, are organic in nature as they contain molecules such as carbohydrates, proteins, and fats—all of which contain carbon atoms. Also, all materials contain chemicals; this term is not meant to refer specifically to manufactured substances.

Ɣ The terms “organic” and “natural” denote substances that are not grown using synthetic materials. However, they may require synthetic materials in their use, e.g., cloth diapers need synthetic detergents for washing, and plastic for packaging.

Ɣ The term “chemical” should mean any material substance, no matter its source. There is no substance that does not contain chemicals. In the media and common usage, the term

“chemical” often refers to synthetic chemicals, mistakenly implying that natural substances are not chemicals.

11. Starch and cellulose are both polymers of glucose and, when burned, both produce carbon dioxide and water, with the same energy released. Humans can only break down starch and lack the ability to break down cellulose. Thus, cellulose remains unchanged in humans, with no release of energy. Starch can be broken down in humans to produce energy.

12. Sugars are small molecules with many hydroxyl groups, making them readily soluble in the aqueous sap. Tree trunks are mainly cellulose, which are long linear polymer chains of glucose, packed tightly together by inter-chain hydrogen bonds, making them rigid and insoluble in water.

13. Paper or Plastic Bags Paper:

Ɣ Advantages—made from renewable resources, e.g., wood fibres; biodegradable and decomposes in a short time, releasing the atoms and molecules to be recycled; strong; can be reused in many applications, e.g., wrapping parcels.

Ɣ Disadvantages—can rip easily; becomes soggy when wet; not waterproof.

Plastic:

Ɣ Advantages—strong and flexible; waterproof; can be reused in many applications, e.g., as garbage bags; less bulky than paper bags when folded for storage; low cost.

Ɣ Disadvantages—made using nonrenewable resources; not readily decomposed; takes up space in landfill sites.

14. (a) addition polymerization

(b) condensation polymerization

(c) condensation polymerization

(d) condensation polymerization

15. (a) (C

H

O

)

+ nH

O o nC

H

O

o 2nC

H

OH + 2nCO

(b) (C

H

O

)

+ n H

O o n C

H

O

o 3n CH

OH + 3n CO

Extension 16.

Each of the two carboxyl groups in the acid can combine with one of three hydroxyl groups in a condensation reaction. The polymer product will grow into a large 3-D molecule.

17. Two functional groups are a carboxyl group and a hydroxyl group or amino group.

18. Low-carbohydrate and low-sugar diets will have similar effects, as sugars are part of the

carbohydrate family. Giving up candy and snacks, which are high in simple sugars that are

quickly digested by the body, can be better than removing vegetables, cereals, and pastas

because they contain complex carbohydrates that slowly release energy over time. Simple

sugars are quickly absorbed, forcing the body to store the energy while starches promote a

steadier blood sugar level. A better approach to weight loss would be to increase healthy activity and eat a well-balanced, nutritious diet.

19. (a-c) Natural rubber is produced from the sap of the rubber tree, Hevea brasiliensis, found in the Amazon Basin. An alternative source is Castilloa, which is native to Mexico.

The sap is collected, exposed to air, and gently heated. This process has been used by Aboriginal peoples of Mexico and Peru for over two thousand years. There is some record of rubber being made into balls and used for ritual games by the Olmec people of Central America. It was likely also used to make shoes and containers for liquids.

Natural rubber is a polymer of 2-methylbuta-1,3-diene (isoprene), CH

=C(CH

)CH=CH

.

The polymerization reaction is:

n CH

=C(CH

) CH=CH

o [CH

C(CH

)=CHCH

]



Charles Goodyear developed the vulcanizing process in which rubber is heated with sulfur. This process produced a more elastic and stable rubber and made it suitable for a wide range of products such as cushions, raincoats, and shoes. Rubber is primarily used in car tires, and a filler such as carbon black is added for reinforcement.

Synthetic rubber was developed and produced in Germany during World War I, and demand for materials increased research and production of new synthetic rubbers during World War II.

20. Dr. Raymond Lemieux had a wide variety of interests in organic and biochemical sciences.

His many achievements include: pioneering work on nuclear magnetic resonance (NMR) technology, discoveries in antibiotics, founding a number of successful companies, work with blood determinates, development of new organ anti-rejection drugs, and improved treatments for leukemia and hemophilia.

21. [Answers will vary.] In 2006 a series of new petrochemical projects was announced,

involving companies such as Sherritt International (a recycling company that handles

polypropylene) and Shell Chemicals Canada (producers of monoethylene glycol and styrene

monomer).