14. As shown on the map, the nearest ethane extraction sites to Lethbridge are to the

14. As shown on the map, the nearest ethane extraction sites to Lethbridge are to the

southeast (Milk River area) and northeast (Medicine Hat area).

From social and economic perspectives it can be said that the gas plants provide jobs for people who both support and earn a living from local businesses.

15. There is a huge range in educational requirements for jobs in Alberta ethane companies. (For example, professional jobs at Dow Chemicals require a university degree.) Administrative and technical support positions require a secondary school education as well as the completion of vocational associate degree/certificate, apprenticeship or trades training. Specialized training in chemical or mechanical

technologies is also desirable.

ATCO takes university engineering students on co-op work-experience placements.

[See Table 2 in Section 10.1

(Student Book page 415) for a list of some ethane producers in Alberta, e.g., in Joffre, Edmonton, Cochrane, and Empress Alberta.]

16. Being able to move the molecules helps me to understand the angles between the atoms. In a book it looks as though the molecules are flat, but when you turn them around you see that they are not. It is easier to see how some molecules with polar bonds are polar molecules, but others are not.

9.4 AROMATICS

Web Activity: Web QuestWest Nile Denial (Page 383)

[The following responses are samples. Other answers should also be considered. The responses should be presented in a brochure.]

Compounds that have been, or are being, used as mosquito repellents

Ɣ DEET, picaridin, pyrethrins, citronella, oil of lemon eucalyptus, catnip, and garlic are all used

as mosquito repellents. Many of them are aromatic molecules, containing a benzene ring. If

chemists were to engineer a new synthetic repellent compound, the molecule would probably

contain at least one benzene ring.

Safety warnings concerning the use of specific repellents

Ɣ DEET is considered relatively safe for adults, providing it is not ingested. There are concerns regarding its use on children and animals, however, as they may be more likely to ingest it.

All repellents should be washed from the hands before touching food. It is possible that natural substances could be safer than synthetic compounds. Pyrethrins (naturally sourced) are toxic however, so one cannot assume that all natural compounds are safe. One concern with nonpolar compounds is that, being fat soluble, they could perhaps accumulate in the body.

Recommendation for a safe and effective way to minimize the risk of mosquito bites Ɣ Adults should use a mosquito repellent containing at least 20% DEET if they go outside at

dawn and dusk, or if they are going into a mosquito-infested area, during the months when mosquitoes are particularly active. Long pants and long-sleeved shirts, in light colours, should also be worn.

Ɣ Children under 12 should also wear suitable clothing during times when mosquitoes are active. A natural mosquito repellent, such as citronella oil or oil of lemon eucalyptus, could also be applied to places they are less likely to touch, such as the back of the neck and the ankles. Avoid putting chemicals on a child’s hands and face.

Lab Exercise 9.A: Chemical Properties of Aliphatics and Aromatics (Page 384)

Purpose

The purpose of this investigation is to test the generalization that aromatic hydrocarbons react like saturated rather than unsaturated hydrocarbons.

Problem

What is the order of reaction rate for cyclohexane, cyclohexene, and benzene?

Prediction

Since benzene behaves chemically as if it were saturated rather than unsaturated, benzene and cyclohexane should react similarly and resist oxidation by permanganate. Since alkenes are generally more reactive due to their unsaturated bonds, cyclohexene should react quickly with permanganate.

Analysis

The rapid colour change in cyclohexene indicates that the reaction occurred immediately. The other liquids showed no initial reaction, as expected. However, the slight colour change in cyclohexane suggests that a chemical reaction may have occurred, although slowly. On the basis of the evidence, the order of reaction rate from lowest to highest, is benzene, cyclohexane, and cyclohexene.

Evaluation

The prediction is judged to be verified since the evidence gathered supported the prediction made.

Since the prediction is verified, the generalization that aromic hydrocarbons react like saturated rather than unsaturated hydrocarbons is judged to be acceptable.

The purpose of the investigation was accomplished although, as always, further tests

should be completed.

Lab Exercise 9.B: Boiling Points of Sample Aliphatics and Aromatics (Page 384)

Purpose

The purpose of this lab exercise is to test the ability of London forces to predict the relative boiling points of aliphatic and aromatic hydrocarbons.

Problem

What is the relative order of boiling points of simple C

alkane, alkene, cycloalkane, cycloalkene, and aromatic hydrocarbons?

Prediction

According to intermolecular bonding theories, hydrocarbons have nonpolar molecules and should have only London forces among the molecules. Based on the theoretical rule that the strength of London forces is related only to the number of electrons per molecule, the order of strengths of London forces from weakest to strongest should be benzene, cyclohexene, cyclohexane/hex-1- ene, and hexane. Because the strength of intermolecular forces is believed to relate directly to boiling point, this order should also be the order of increasing boiling points.

Name Molecular formula # e

per molecule

benzene C

H

42 cyclohexene C

H

46 cyclohexane C

H

48 hex-1-ene C

H

48 hexane C

H

50

Analysis

According to the evidence gathered, the order of boiling points, from lowest to highest, is hex-1- ene, hexane, benzene, cyclohexane, and cyclohexene.

Evaluation

The prediction is clearly judged to be falsified because the experimental result bears little resemblance to the predicted order. It does not seem likely that any experimental uncertainties in measuring the boiling points could account for this difference. The concept of London forces, including the simple rule of counting electrons per molecule as a predictive tool, is judged to be unacceptable in this experiment. The molecules may be too close to the same size and other factors are influencing the results. The next step may be to create a replacement or revised concept although, for now, we should just know that the concept does not predict well when the boiling points and the molecules are similar.

The purpose of the investigation was met; our simple intermolecular force theory was tested.

Section 9.4 Questions (Page 385)

1. The simplest aromatic compound is benzene, C

H

. An unusual structural feature of benzene

is the circle in the centre of the six-sided ring. This represents six “extra” electrons shared by

all carbon atoms in the ring. This is the best explanation that chemists have found for the

chemical formula and the chemical reactions of benzene.

2.

3. (a) (b) (c)

(d)

4.(a) (b) (c)

[Note: The three xylenes are respectively ortho-, meta- and para-dimethylbenzene. This nomenclature is not required for this course.]

5. (a) 1-ethyl-3-methylbenzene

(b) 1-methyl-4-propylbenzene

[Some alternative names are allowed, depending on order of numbering in structure and order of branches in names]

6. (a)

propylbenzene o methylbenzene + ethene (b) ethylbenzene o 1,2-dimethylbenzene (c) benzene + ethene o ethylbenzene 7. (a) aliphatic

(b) aromatic (c) aliphatic

(d) aliphatic [name should be 4-methylpent-2-yne]

(e) aromatic (f) aliphatic 8. (a) unsaturated

(b) saturated

(c) saturated [based on low reactivity like alkanes]

(d) unsaturated (e) saturated

(f) saturated (based on low reactivity like alkanes)

9. This is not an appropriate name for benzene because the physical and chemical properties of benzene suggest that it has no double bonds. For example, each of the carbon-carbon bonds in the benzene are identical in both length and strength, suggesting that the bonds are identical rather than alternating single and double bonds. Furthermore, benzene does not undergo addition reactions that are characteristic of unsaturated hydrocarbons. Instead, benzene undergoes substitution reactions, which are characteristic of saturated hydrocarbons.

10. Knowing the experimental result does not help to explain the order of boiling points using London forces. This concept does not work in this example perhaps because the numbers of electrons per molecule are very similar. To explain the order some other concept is required.

A possibility might be to add the concept of molecular shape that may affect how close the molecules can get to one another.

11. Ɣ Common sources of benzene exposure: Since benzene is a naturally occurring component of crude oil, it can enter groundwater and soil through seepage of oil, either from a pool of crude oil in the ground or an accidental oil spill. Benzene can also be made during the incomplete combustion of organic materials. A major source of benzene in the

atmosphere is the incombustion of gasoline and diesel fuels. Even cigarette smoke is known to contain traces of benzene. At one time benzene was intentionally added to gasoline to improve performance. Now gasoline is restricted to having less than one percent benzene. Benzene has generally been replaced as a solvent or reactant, for example in schools, by toluene. Since benzene is a common industrial solvent, many industrial processes are potential sources of benzene exposure.

Ɣ Short-term health effects: vomiting, dizziness, nausea, reduction in blood pressure, depression of the central nervous system.

Ɣ Long-term health effects: bone marrow depression, anaemia, leukemia, and liver and

kidney toxicity.