Ɣ Technological: Many organic halides are important chemicals for use in various industries or serve a useful purpose such as pest control.

Extension

5. (a) Hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) are alternatives to chlorofluorocarbons (CFCs) that are still in use. They appear to be less damaging to the ozone layer than CFCs (although the “hole” in the ozone layer is still growing). However, HCFCs and HFCs may act as greenhouse gases (GHGs), possibly leading to global warming.

(b) An aerosol can is designed with a pump-action top so that the can will be pressurized with air when necessary. The contents to be sprayed can be pre-packaged into the can or added by the consumer. The marketing strategy will focus on environmental safety (no propellant added to the atmosphere to decrease the ozone layer or increase global warming) and economy (re-usable for a variety of ingredients).

6. Pro Perspectives

Ɣ Technological: Many organic halides are important chemicals for use in various industries or serve a useful purpose such as pest control.

Con Perspectives

Ɣ Ecological: Many organic halides are toxic and many are also carcinogenic. Some organic halides have caused and continue to cause the depletion of the ozone layer.

7.

8. Toxicity of organic halides depends on the specific compound and whether it interferes with necessary biological processes. Toxicity also depends on the concentration of the compound.

For small organic halides that are somewhat polar, their water solubility will mean that the organic halide has a good chance of being excreted from the body of an organism. However, larger organic halides whose composition is mostly hydrocarbon tend to have a very low water solubility and a very high fat solubility. Ingesting fat-soluble organic halides likely means that they will be stored in the fatty deposits of an organism and not excreted. The concentration slowly increases above the local environmental level in a process called bioaccumulation. As small organisms like algae are consumed by larger organisms like water fleas, bioaccumlation is magnified. Going up the food chain from water fleas to minnows to larger fish to eagles or humans, the concentration of fat-soluble organic halides is magnified at each step, resulting in final concentrations that may be lethal or cause serious effects (e.g., reproductive). The classic case of this biomagnification is dichloro diphenyl trichloroethane (DDT). Another common organic halide example is polychlorinated biphenyls (PCBs).

10.3 ALCOHOLS AND ELIMINATION REACTIONS

Practice (Page 426)

1. The introduction of alcohols into gasoline has a number of roles. Alcohols contain oxygen,

and when mixed with gasoline in the combustion chamber of the engine they burn more

completely and produce less carbon monoxide. Alcohols increase the octane rating of the

fuel, allowing the engine to run more efficiently. Alcohols are also hydrophilic, which means

that they can absorb and dissolve water into the fuel. This keeps any condensation of water in

the gas tank from freezing the gas lines.

2. Pro Perspectives

Ɣ Social: The mandatory addition of ethanol into gasoline would conserve more

petrochemicals for future generations, as the added ethanol is a renewable resource while the petrochemical portion is not.

Ɣ Political: The mandatory addition of alcohol into gasoline would allow politicians to spread out the benefits from gasoline production to include agricultural areas.

Ɣ Economic: The mandatory addition of alcohol into gasoline would give farmers, and their support businesses, an economic boost as farmers would be able to produce and sell the grains for the fermentation process.

Con Perspectives

Ɣ Social: Many people are against more regulation and prefer choices in the products they buy.

Ɣ Political: The mandatory addition of alcohol into gasoline could affect the career of politicians due to the very large voting population of the province interpreting the increased cost of fuel as a major problem.

Ɣ Economic: The mandatory addition of alcohol into gasoline may cause the production of automotive fuel to increase due to the cost of alcohol production.

3. (a) 6 CO

(g) + 6 H

O(l) o C

H

O

(aq) + 6 O

(g) (b) n C

H

O

(aq) o [C

H

O

]

(s) + n H

O(l) (c) [C

H

O

]

(s) + n H

O(l) o n C

H

O

(aq) (d) C

H

O

(aq) o 2 CO

(g) + 2 C

H

OH(l)

4. To have greater volatility (ability to vaporize), the intermolecular forces between the molecules must be lower. In other words, an order of increasing volatility is predicted to be the order of decreasing intermolecular forces if molecular sizes are approximately the same.

The order of increasing volatility is therefore: alcohols, organic halides, and hydrocarbons.

Practice

(Pages 430–431) 5. (a) butan-2-ol

(b) pentan-2-ol

(c) cyclohexane-1,3-diol

6. (a) (b)

(c) (d)

7. (a) (b)

8. The presence of a hydroxyl group in methanol makes the molecule more polar than methane, and allows hydrogen bonding between molecules. This increase in intermolecular forces results in a higher boiling point.

9. (a) In order of their increasing boiling point: ethane, fluoromethane, methanol.

The order of the boiling points depends on the order of the strengths of the intermolecular forces that exist among molecules in a substance. All substances will have London forces with strengths depending on the number of electrons per molecule. Since the number of electrons in these substances is the same, the observed trend depends on the presence of other intermolecular attractions. Ethane has only London forces among its molecules.

Both fluoromethane and methanol consist of polar molecules with dipole–dipole forces.

Methanol has the highest boiling point because it also has hydrogen bonding.

(b) In order of increasing boiling point: pentane, 1-chlorobutane, butan-1-ol.

All molecules have a similar number of electrons. Pentane has the lowest boiling point because its molecules are nonpolar and, as a result, have only London forces between them. The higher boiling point of 1-chlorobutane is a result of dipole–dipole forces between its molecules, in addition to its London forces. Butan-1-ol has the highest boiling point because its molecules attract each other with all three types of intermolecular forces, in particular hydrogen bonding.

10. Each molecule of glycerol contains three hydroxyl groups which can hydrogen-bond with water, interfering with the attractions between water molecules and thus interfering with the freezing of water. When water in tissues does not freeze, there is less damage to the tissues.

11. (a)

As the strength of intermolecular forces increases, the boiling point also increases, due to the increase in attraction between the molecules. To vaporize, the molecules with higher forces need more energy. Since ethane only has London forces and also has the fewest number of electrons (18), it has the weakest intermolecular forces. Chloroethane has more electrons (34) than ethane, and is polar due to the chlorine, so will rank next in strength of intermolecular forces. Ethanol, due to its hydrogen bonding, will have the strongest intermolecular force even though it has slightly fewer electrons (26) than chloroethane.

[Boiling points are: ethane (-88.6 °C), chloroethane (12.3 °C), ethanol (78.5 °C)]

(b) The solubility of molecules in water is dependent on the strength of attraction between the molecule and the water. Ethanol is not only polar but is capable of hydrogen bonding with water molecules. Ethanol should have the highest solubility in water. Chloroethane is the next most soluble because it is polar due to the chlorine atom. Polar molecules tend to be at least partially soluble in polar water. Ethane would be the least soluble in water because it is nonpolar.

12. (a) CH

(g) + H

O(l) o CO(g) + 3 H

(g) (b) CO(g) + H

(g) o CH

OH(l)

13. (a) (b)

14. (a) CH

CH

OH(l) + 3 O

(g) o 2 CO

(g) + 3 H

O(g) (b) 2 CH

– OH(l) + 3 O

(g) o CO

(g) + 2 H

O(g) 15. (a) 5.0% u 355 mL = 18 mL

(b) 12% u 150 mL = 18 mL

(c) 40% u 45 mL = 18 mL

(d) The volume of ethanol is the same in each of these drinks.

16. Ethanol is denatured to make it unfit for human consumption. The intention is to reduce the problems of intoxication or at least to reduce the problem linked with products sold only in licensed establishments. This practice of denaturing allows for alcohol used as a solvent or an additive to be sold at a lower cost (without significant government taxes).

17. Purpose

The purpose of this investigation is to test intermolecular bonding theories.

Problem

What are the relative boiling points of 1-butanol, methanol, 1-propanol, and ethanol?

Prediction

According to intermolecular bonding theories, the predicted order of increasing boiling points is methanol, ethanol, 1-propanol, and 1-butanol. All four alcohols contain one hydroxyl group and therefore have very similar dipole–dipole and hydrogen bonding forces. If we consider those forces approximately equal, then London forces must account for differences in boiling point. The four alcohols, methanol (18 e

), ethanol (26 e

), 1-propanol (34 e

), and 1-butanol (42 e

) have an increasing number of electrons and, therefore, an increasing strength of London forces.

Evidence

According to the CRC Handbook of Chemistry and Physics, the respective boiling points are:

Chemical Boiling point (qC)

1-butanol 117 1-propanol 97

ethanol 79 methanol 65

Evaluation

According to the evidence, the order is exactly the same as the Prediction. Therefore, the Prediction is judged to be verified and the intermolecular bonding theories clearly appear to be acceptable.

Practice (Page 433) 18.

19. (a)

(b)

(c)

20.

21. (a) One solution to the problem of having too much ethane remaining as the chemicals are removed from the cracker is to separate the ethane and ethene, and then reintroduce the ethane into the cracker.

(b) One solution to the problem of producing ethyne along with ethene would be to remove the chemicals more quickly, before ethene has a chance to convert to ethyne. By removing the chemicals early, there is a good chance that there will be a significant amount of ethene that has not been converted to ethyne.

(c) One solution to the problem of producing methane and hydrogen instead of ethene during the cracking of ethane is to change the conditions of the reaction, including the reaction pressures, temperatures, and/or the catalysts.

Investigation 10.2: Isomers of Butanol (Pages 433, 462)

Purpose

The purpose of this investigation is to test a personal hypothesis about the relative reactivity of the alcohol isomers of butan-1-ol.

Problem

What is the difference in reactivity, if any, of the alcohol isomers of butan-1-ol with concentrated hydrochloric acid?

Hypothesis

The relative reactivity of the isomers of butan-1-ol depends directly on the number of hydrogen atoms attached to the same carbon as the hydroxyl group. The more hydrogen atoms attached to the carbon, the faster the reaction will be.

Prediction

According to the hypothesis, the order of reactivity from greatest to least is butan-1-ol, butan-2- ol, and 2-methylpropan-2-ol. Since hydrogen has a lower electronegativity than carbon, the primary alcohol will have a greater negative charge on the oxygen and, therefore, the hydroxyl group will be easier to replace. The secondary alcohol will have the second fastest reaction because it has only one hydrogen attached to the carbon containing the hydroxyl, while the tertiary alcohol has no hydrogens on that carbon and will have either very little reaction or none.

Materials

Ɣ lab apron

Ɣ eye protection

Ɣ gloves

Ɣ butan-1-ol (pure) Ɣ butan-2-ol (pure)

Ɣ 2-methylpropan-2-ol (pure) Ɣ concentrated HCl(aq) (12 mol/L) Ɣ 3 test tubes with stoppers

Ɣ test-tube rack Ɣ 4 eye droppers

Ɣ labelled disposal container

CAUTION: 12 mol/L hydrochloric acid is very corrosive. Protective clothing (including gloves) must be worn.

Evidence

Alcohol Reaction with HCl(aq) butan-1-ol no changes observed butan-2-ol no changes observed 2-methylpropan-2-ol cloudy white mixture formed

Analysis

According to the evidence collected, 2-methylpropan-2-ol was the only isomer to react. Neither butan-1-ol nor butan-2-ol appeared to react.

Evaluation

The design does not appear adequate to answer the problem. An improvement to the design would be to have a more specific and precise diagnostic test for the formation of an alkyl halide.

The materials are judged to be adequate for the given design but might be improved with a heating device to warm the mixtures. The procedure was barely adequate to collect sufficient evidence. Improvements required include (i)use of larger volumes of reactants to make the different layers more visible and (ii)possibly heating the mixture. (There were no special technological skills required.) On the basis of my evaluation of the experiment, I am not certain of the results. The major sources of uncertainty are the difficulty of seeing changes with small quantities of reactants and the lack of a more specific diagnostic test for alkyl halides.

It is not possible to judge the prediction because the evidence is insufficient to answer the problem. Therefore the hypothesis remains untested and the purpose was not accomplished.

Another experiment with an improved design is required.

Web Activity: Web Quest—Cellulosic Ethanol (Page 434)

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

Environmental impact of building the plant

Every construction project has an environmental impact. This impact can be reduced, however, by having it situated away from environmentally sensitive areas and by using eco-friendly (e.g., recycled) products in the construction. The use of heavy equipment should be kept to a minimum, and waste materials should be re-used or recycled.

Environmental impact of using ethanol as a fuel

Ethanol in fuel has a number of environmental advantages. It contains oxygen and, when burned alone or blended with gasoline in a vehicle engine, contributes to more complete combustion and lower carbon monoxide emissions. Ethanol can replace other fuel additives, such as methyl tertiary-butyl ether (MTBE), which is being phased out due to groundwater contamination.

Using pure ethanol in engines will reduce the carbon dioxide emissions, for the same

distance travelled, by about 13%.

Biomass is the main ingredient in the production of cellulosic ethanol. The production of biomass by plants, involves the removal of carbon dioxide from the air. Although this carbon dioxide is returned to the air when the ethanol is burned, there is an environmental advantage (a reduction in GHGs) to this process during the growing period. This contrasts with the combustion of ethanol sourced from petroleum products, which releases only carbon dioxide.

Ethanol is more stable and less likely to catch fire than gasoline, and spilled ethanol is much less toxic to the environment as it can be diluted with water because it is a polar molecule.

Environmental spills, when diluted, can be metabolized by aquatic organisms without causing serious damage.

Taking into account all the energy costs in producing ethanol, industry can obtain approximately 38% more energy from a litre of ethanol than is put into the process, when using fermentation of food-source sugars. Cellulosic ethanol production can release approximately 162% more energy than is consumed in its production. This means that, even though it may require petroleum products to help produce ethanol (pesticides, fertilizer, tractor fuel, etc.), there is a net energy gain.

Availability of biomass and how it is transported to the plant

Biomass is available from many sources, including pulp mills and farms. It can be a waste product (such as plant waste) or a specially grown crop (such as corn). Of course, if a

considerable quantity of energy is expended, and pollution is produced, in the production and transportation of the biomass, then any benefit gained by its conversion into ethanol is negated.

There has to be a careful balancing of the input and output of energy and the overall pollution that is released.

Depending on the study, there seems to be conflicting evidence and a wide variety of points of view on this issue. However, it seems that there is an energy gain of approximately 38%

(industry average) from producing ethanol from corn (starch fermentation), while there is a 162%

energy gain (predicted) from producing ethanol from cellulose.

Economic impact of producing large quantities of ethanol at the plant

There may be a large economic impact with the increased use of ethanol, depending on petroleum fuel prices and the cost of producing ethanol.

As petroleum becomes more expensive, using a renewable resource such as ethanol (as long as it is not too expensive to manufacture) becomes a viable alternative. Currently,

approximately 27% of the total energy consumption in Canada comes from transportation machinery. These machines mostly use liquid fuels (gasoline, diesel, or kerosene). Since ethanol is also a liquid, it can be used in current engine designs. In fact, automobile engines can already use 10% ethanol blends (E10) and, with minor modifications, will be able to use 85% blends (E85).

In Alberta, ethanol is currently produced by either hydration of ethene or fermentation of plant starch/sugar. So far, these methods have not been widely adopted for use as fuels. Studies have shown that fermentation of starch to produce fuel-grade ethanol costs approximately

$41/barrel (2005), compared with the average crude oil price of $54/barrel.

Currently, cellulosic ethanol costs more per litre than does ethanol produced by

fermentation, at about $0.52CND per litre, or $1.50US per gallon in 1999 dollars. This higher

cost is largely attributed to the cost of developing the technology, developing the enzymes, and

mass-producing the enzymes. As more plants are built, and as the technology matures, it is

expected that the cost per litre will drop below the cost for starch fermentation. One reason for

this prediction is that, while starch is primarily grown for food, plant cellulose is not digestible by

humans and is therefore cheaper to purchase. Usually, the parts of the plant that cannot be used as

food are burned or discarded. These “wastes” can be turned into valuable ethanol. Harvesting the

whole plant, selling the starchy parts for food, and selling the cellulose for ethanol production

makes farming much more profitable.

Another economic consideration is that ethanol production, either from starch or cellulose, can move the fuel production profits from petrochemical companies to agricultural areas. Farmers and even cities can get into the business of energy production: farmers can sell excess biomass, while cities can recycle garden and paper waste. Even forestry and pulp/paper industries can use this technology to generate ethanol, creating profit from wastes that are byproducts of their production.

A further economic consideration is the cost of transporting biomass to the ethanol plant and of transporting ethanol to consumers. Finally, the lower energy density of ethanol (two-thirds the energy of the equivalent mass of gasoline) reduces the range of ethanol-powered vehicles.

Technology behind the production of cellulosic ethanol

Cellulosic ethanol has exactly the same chemical structure as ethanol that is made through fermentation or petrochemical processes. Cellulosic ethanol is made from the non-food portion of renewable feedstocks such as cereal straws, corn stover, and fast-growing trees such as poplar, and grasses. There are two main methods in cellulosic ethanol production: enzymatic hydrolysis and a gasification process.

In enzymatic hydrolysis, the cellulose in the biomass is converted into sugars, while the lignin in the plant fibre (the portion that cannot be converted to ethanol) is used to generate steam and electricity to fuel the process. This eliminates the need for fossil fuels such as coal or natural gas. Yeast metabolizes C

(hexose) sugars into ethanol. Since hemicellulose breaks down to produce both C

and C

sugars, microorganisms are used to convert the pentose sugars into ethanol. One example of such an organism is one developed (and patented) by the University of Florida, which is capable of fermenting both C

and C

sugars. Once produced, the ethanol is distilled and filtered into a fuel-grade product that can be blended into automobile fuel.

In the gasification process, cellulose is converted into carbon monoxide instead of sugar molecules. Microorganisms consume the carbon monoxide in a fermenter to produce ethanol, hydrogen, and water.

Ethanol production methods

1. Fermentation uses yeast (Saccharomyces cerevisiae) to metabolize sugar in the absence of oxygen into ethanol and carbon dioxide. The overall chemical reaction is:

yeast

6 12 6 2 5 2

C H O  o 2 C H OH + 2 CO .

Since yeast will die once the concentration of ethanol reaches about 25%, any further concentration must be done through distillation.

2. The ethene hydration reaction is catalyzed by an acid. The typical reaction is:

acid

2 4 2 2 5

C H + H O o C H OH .

This method uses considerable quantities of petrochemicals, some as feedstock (ethene) and some as the fuel to drive the process. This method, with lower fuel prices, was more

economical than fermentation. However, with higher fuel prices, this method has become less favourable.

Section 10.3 Questions (Page 435)

1.

2. Propane is a nonpolar hydrocarbon with weak intermolecular forces; thus it has a low boiling point and is a gas at room temperature. Propan-2-ol is an alcohol, with a polar hydroxyl group and strong intermolecular hydrogen bonds, thus it has a higher boiling point than propane and is a liquid at room temperature.

3.

4. (a)

(b)

5.

6. (a) addition:

(b) elimination (dehydration):

(c) addition:

(d) combustion:

7.

[Alternatively, two separate chemical equations can be written. This would be a better representation because the relative yields of the two products are not equal.]

8. (a) butane

(b) methylpropane (or 2-methylpropane)

(c) but-2-ene

(d) methylpropene (or 2-methylprop-1-ene) (e) butan-1-ol

(f) butan-2-ol

(g) methylpropan-1-ol (or 2-methylpropan-1-ol) (h) methylpropan-2-ol (or 2-methylpropan-2-ol)

9. (a) (b)

(c) (d)

10. Purpose

The purpose of this investigation is to test a hypothesis concerning the relative boiling points and solubility of alcohols.

Problem

(a) What is the trend in boiling points for C

– C

primary alcohols?

(b) What is the trend in solubility for C

– C

primary alcohols?

Hypothesis

As the number of electrons per molecule increases for each alcohol, the boiling point will increase due to the increasing strength of London forces. Also, as the number of carbon atoms per molecule increases, the nonpolar portion of the molecules becomes larger, decreasing the solubility of the alcohol in the polar water.

Analysis

According to the evidence, the boiling point increases from methanol to hexan-1-ol and the solubility decreases from methanol to hexan-1-ol.

Evaluation

The hypothesis is judged to be acceptable because the evidence provided clearly agrees with the trends expected. The purpose was accomplished.

11. Pro Perspectives

Ɣ Scientific: Alcohols are frequently used as solvents in organic reactions because they are effective for both polar and non-polar compounds.

Ɣ Technological: Increasingly, one of the most important technological applications of alcohols is as a gasoline additive.

Ɣ Economic: Grain-based ethanol plants are adding another significant market for grain farmers.

Ɣ Political: Provincial legislation to include 10% ethanol in gasoline, and tax incentives, will accelerate the expansion of the ethanol industry.

Con Perspectives

Ɣ Ecological: It is better for the environment to produce alcohols from renewable plant materials than to produce them from nonrenewable fossil fuels.

Extension

12. (a) 2 CH

OH(l) + 3 O

(g) o 2 CO

(g) + 4 H

O(g)

CH

CH

OH(l) + 3 O

(g) o 2 CO

(g) + 3 H

O(g)

(b) Methanol and ethanol, having both polar hydroxyl groups and nonpolar carbon chains, are soluble in both water and in gasoline; thus water droplets are dissolved in the alcohol and do not form ice, which blocks gasoline flow.

13. (a)

(b) Ethylene glycol is a better choice as a radiator antifreeze and coolant than ethanol because it has a much higher boiling point (197 °C vs 79 °C) due to its stronger London forces and hydrogen bonding. A mixture of ethylene glycol and water can be heated to a higher temperature before it boils, compared to a mixture of ethanol and water. Ethylene glycol also has a larger specific heat capacity than ethanol, which allows for the

absorption of larger amounts of heat from an engine for the same increase in temperature.

(c) Methanol, rather than ethanol glycol, is used as a windshield wiper antifreeze for three reasons. First, ethylene glycol has a higher melting point (–13 °C vs –97 °C), which means it is likely to get too viscous or even freeze at temperatures that can occur during winter. Second, ethylene glycol is more viscous than methanol, which could make clearing the liquid from the windshield a problem. Spilled or sprayed ethylene glycol, with its higher boiling point and lower volatility, evaporates very slowly compared to methanol, which evaporates much more quickly.

(d) According to the Material Safety Data Sheet (MSDS) references, methanol is more toxic than ethylene glycol. The lowest reported lethal dose for a human is 428 mg/kg for methanol and 786 mg/kg for ethylene glycol.

(e) A 50:50 dilution of ethylene glycol in water has a freezing point of –37 °C.

10.4 CARBOXYLIC ACIDS, ESTERS, AND ESTERIFICATION REACTIONS

Lab Exercise 10.B: Explaining Physical Property Trends (Page 437)

Purpose

The purpose of this investigation is to use your knowledge of organic structures and intermolecular forces to explain some physical properties of alcohols and carboxylic acids.

Problem

What is the explanation for the trends in boiling points and solubilities in water within and between series of simple alcohols and carboxylic acids?

Analysis

Ɣ The boiling point increase of methanol (65 qC) to pentan-1-ol (137 qC) can be explained by

the increase in the size of the molecules and the number of electrons. As the size increases,

the strength of the London forces increases, which means that the strength between molecules

increases, which in turn causes an increase in boiling points. The dipole–dipole and hydrogen

bonding forces should be approximately the same for all the alcohols.