Download Ex. 32 Answer

New 21st Century Chemistry
Suggested answers to in-text activities and unit-end exercises
Topic 8 Unit 32
In-text activities
Checkpoint (page 168)
1
Suggested answers to in-text activities and unit-end exercises
Topic 8 Unit 32
1
© Jing Kung. All rights reserved.
New 21st Century Chemistry
2
Discussion (page 169)
1 Hydroxyl group
2
3
4
Addition of bromine to an alkene
An alkene
Suggested answers to in-text activities and unit-end exercises
Topic 8 Unit 32
2
© Jing Kung. All rights reserved.
New 21st Century Chemistry
5
Checkpoint (page 172)
a)
b)
c)
d)
Checkpoint (page 175)
1 a) CH3CH2CH2CH2Cl / CH3CH2CH2CH2Br / CH3CH2CH2CH2I
2
b) Cl2, ultraviolet light or heat
c) 85% H3PO4, 165 – 170 °C
d) H2O / H3O+
a)
Suggested answers to in-text activities and unit-end exercises
Topic 8 Unit 32
3
© Jing Kung. All rights reserved.
New 21st Century Chemistry
b)
c)
d)
Discussion (page 177)
This discussion aims at raising students’ awareness of the principles of green chemistry. See the
following list of green chemistry principles the discussion questions help to convey.
1
2
3
4
5
Safer auxiliary substances — Whenever possible, avoid the use of auxiliary substances such as
solvents and separating agents. When these substances are needed, they should be non-toxic.
Energy efficiency — Energy efficiency should be considered when designing and producing a
product.
Safer auxiliary substances — Whenever possible, avoid the use of auxiliary substances such as
solvents and separating agents. When these substances are needed, they should be non-toxic.
Safer auxiliary substances — Whenever possible, avoid the use of auxiliary substances such as
solvents and separating agents. When these substances are needed, they should be non-toxic.
Use of renewable resources — When possible, the feedstocks should come from a renewable
resource.
Checkpoint (page 189)
a) Place the mixture in a separating funnel. Allow the two layers to separate. Run the aqueous layer
into a beaker.
b) No more gas bubbles are given off.
c) To dry the organic product.
The liquid product is clear after the drying process.
Suggested answers to in-text activities and unit-end exercises
Topic 8 Unit 32
4
© Jing Kung. All rights reserved.
New 21st Century Chemistry
d)
e) Number of moles of (CH3)3COH used =
7.10 g
74.0 g mol–1
= 0.0959 mol
= number of moles of (CH3)3CCl formed
Theoretical yield of (CH3)3CCl = 0.0959 mol x 92.5 g mol–1
= 8.87 g
Percentage yield of (CH3)3CCl =
5.50 g
x 100%
8.87 g
= 62.0%
Internet Search & Presentation (page 190)
Aspartame
Aspartame is 200 times as sweet as sucrose. Aspartame is utilized as a low-calorie sweetener in soft
drinks, salad dressings, ready-made meals, table-top sweeteners, and pharmaceuticals.
Suggested answers to in-text activities and unit-end exercises
Topic 8 Unit 32
5
© Jing Kung. All rights reserved.
New 21st Century Chemistry
The three main reactants used in the synthesis of aspartame are
• phenylalanine,
• methanol and
• aspartic acid.
Ester synthesis
Treatment of phenylalanine with methanol in the presence hydrochloric acid causes an esterification
reaction with the carboxyl group on the phenylalanine. The product is the methyl ester of
phenylalanine.
Amide synthesis
The final goal is to react the methyl ester of phenylalanine with aspartic acid to give the dipeptide
structure. A series of reactions is required so that only the carboxyl group near to the amino group
of the aspartic acid is reacted. The carboxyl group on the side chain is protected so that it does not
react.
References:
http://www.chemcases.com/nutra/nutra2.htm
http://www.elmhurst.edu/~chm/vchembook/549aspartame.html
Paracetamol
Paracetamol is a very widely used medicine. It is a mild painkiller and reduces the temperature of
patients with fever. There are many common products containing paracetamol which are available
from pharmacies. Many of them are sold as treatments for the relief of cold and influenza and they
can be bought in a number of different formulations.
Suggested answers to in-text activities and unit-end exercises
Topic 8 Unit 32
6
© Jing Kung. All rights reserved.
New 21st Century Chemistry
Paracetamol is a relatively safe drug but toxic side effects have been observed with high doses
greater than 10 – 15 g. The principal toxic metabolite of paracetamol is N-acetyl-p-benzoquinone
imine (NAPQI). The tripeptide glutathione stored in the liver can combine with this metabolite,
producing an inactive substance. An acute overdose depletes the glutathione. As a result, NAPQI
accumulates and begins to react with proteins and nucleic acids in the liver, eventually causing
irrepairable damage.
The preparation of paracetamol from phenol
Paracetamol can be made in three steps from phenol.
Step 1
Step 2
Step 3
Reference:
http://www.rsc.org/education/teachers/learnnet/pdf/LearnNet/rsc/paracetamol.pdf
Suggested answers to in-text activities and unit-end exercises
Topic 8 Unit 32
7
© Jing Kung. All rights reserved.
New 21st Century Chemistry
Ibuprofen
Ibuprofen is one of the commonly used anti-inflammatory agents. It is used to relieve the symptoms
of a wide range of illnesses such as headaches, backache, period pain, dental pain, neuralgia,
rheumatic pain, muscular pain, migraine, cold and flu symptoms and arthritis.
Boots process
The Boots process is an older commercial process of obtaining ibuprofen developed by the Boot
Pure Drug Company. The Boots Company patented the process in 1960s. This synthesis consists of
six steps and resulted in unwanted by-products.
Source: http://www.scheikundeinbedrijf.nl/content/Modules/Modulenaam/Files/case.pdf
Suggested answers to in-text activities and unit-end exercises
Topic 8 Unit 32
8
© Jing Kung. All rights reserved.
New 21st Century Chemistry
Celanese process
In the mid eighties when the patent on ibuprofen was about to run out, other companies began
developing new synthetic methods to produce ibuprofen. During this time, the Hoechst Celanese
Corporation and the Boots Company agreed to a joint venture resulting in the BHC Company.
The Celanese process (hereafter known as the green synthesis) has only three steps and gives fewer
harmful by-products.
Source: http://www.scheikundeinbedrijf.nl/content/Modules/Modulenaam/Files/case.pdf
References:
http://www.rsc.org/education/teachers/learnnet/green/ibuprofen/home.htm
http://www.chm.bris.ac.uk/motm/ibuprofen/synthesis.htm
http://www.scheikundeinbedrijf.nl/content/Modules/Modulenaam/Files/case.pdf
Unit-end exercises (pages 195 – 205)
Answers for the HKCEE (Paper 1) and HKALE questions are not provided.
1 A H2 / Pt catalyst
2
B
C
D
E
A
B
C
D
E
Br2 (in organic solvent)
aqueous bromine
cold dilute KMnO4 / OH–
HI
reflux with conc. HCl + ZnCl2 catalyst; or mix with PCl5; or reflux with SOCl2
reflux with NaOH(aq)
excess conc. H2SO4, 180 °C; or Al2O3, 300 °C
reflux with CH3COOH and conc. H2SO4
reflux with NaOH(aq)
Suggested answers to in-text activities and unit-end exercises
Topic 8 Unit 32
9
© Jing Kung. All rights reserved.
New 21st Century Chemistry
F K2Cr2O7 / H3O+
G 1 LiAlH4 / ethoxyethane
3
A
B
C
D
E
F
2 H3O+
NaOH(aq)
1 LiAlH4 / ethoxyethane
2 H3O+
K2Cr2O7 / H3O+
reflux with CH3OH and conc. H2SO4
reflux with NaOH(aq), separate the products by fractional distillation, obtain the acid by
adding excess mineral acid to the salt of carboxylic acid
NH3(aq)
4
5
G heat
D
B
6
C
7
A Option A —
Option B —
W and Z have the same molecular formula but their atoms are linked in
different order. Hence they are structural isomers.
Oxidation of X produces propanoic acid.
Option C —
Y does not have geometrical isomers. One of the carbon atoms of the C=C
bond has two identical hydrogen atoms attached to it.
Option D — Y undergoes addition polymerization to form polypropene.
8 A (3) 1,2-dibromopropane (CH3CHBrCH2Br) will be obtained if Br2(aq) is used in step 3.
9 C
10 B (1) When preparing ethanal from ethanol, the product should be distilled off from the
reaction mixture once formed. Otherwise ethanal will be further oxidized to form
ethanoic acid.
(3) Ethene and bromine react quickly at room temperature. There is NO need to heat under
reflux.
11 a)
b)
c)
d)
HBr(g); addition
expose a mixture of CH3CH2CH3 and Br2 to ultraviolet light or heat; substitution
reflux with NaOH(aq); substitution
1 LiAlH4 / ethoxyethane
2 H3O+
reduction
12 a) —
b) reflux with conc. HCl + ZnCl2 catalyst; or mix with PCl5; or reflux with SOCl2
c) 1 LiAlH4 / ethoxyethane
Suggested answers to in-text activities and unit-end exercises
Topic 8 Unit 32
10
© Jing Kung. All rights reserved.
New 21st Century Chemistry
2 H3O+
d) NaOH(aq), heat
e) 1 reflux with NaOH(aq)
2 separate the products by fractional distillation
3 obtain the acid by adding excess mineral acid to the salt of carboxylic acid
13 A
B
C
D CH2=CHCH2CH3 or CH3CH=CHCH3
E
14 a) A 1 LiAlH4 / ethoxyethane
2 H3O+
B reflux with NaI + conc. H3PO4; or reflux with red P + I2
b) C excess conc. H2SO4, 180 °C
D HCl
c) E reflux with NaOH(aq)
F reflux with conc. HCl + ZnCl2 catalyst; or mix with PCl5; or reflux with SOCl2
d) G CH3CH2COOH
H
15 —
Suggested answers to in-text activities and unit-end exercises
Topic 8 Unit 32
11
© Jing Kung. All rights reserved.
New 21st Century Chemistry
16 a)
b)
c)
d)
e)
f)
g)
h)
17 —
18 Step 1
Concentrated sulphuric acid is used as a catalyst.
The reaction mixture is heated for about 40 minutes as the reaction is slow.
Suggested answers to in-text activities and unit-end exercises
Topic 8 Unit 32
12
© Jing Kung. All rights reserved.
New 21st Century Chemistry
Step 2
Ester boils below 85 °C.
Step 3
Sodium carbonate solution is added to remove any acid.
Step 4
Anhydrous sodium sulphate or calcium chloride is added to remove water.
Step 5
The 76 °C – 80 °C fraction contains most of the ester.
19 —
20 a) i) Apparatus I — heat under reflux
Apparatus II — distillation
ii) Expansion of vapour would build up pressure. An explosion may occur.
b) i) The reaction is vigorous.
ii) Ethanol and iodoethane are flammable.
iii) To allow time for the reaction to complete. / The reaction is slow.
iv) Between 71 °C – 73 °C
c) i) Number of moles of I2 =
20.0 g
= 0.0788 mol
2 x 126.9 g mol–1
1 mole of I2 can produce 2 moles of iodoethane.
ii) Number of moles of iodoethane formed = 2 x 0.0788 mol
= 0.158 mol
iii) Theoretical yield of iodoethane = 0.158 mol x 156.0 g mol–1
= 24.6 g
Percentage yield of iodoethane =
Suggested answers to in-text activities and unit-end exercises
Topic 8 Unit 32
16.7 g
x 100% = 67.9%
24.6 g
13
© Jing Kung. All rights reserved.
New 21st Century Chemistry
21 a) Shaking and the heat of the hands may cause the liquid inside the separating funnel to
vaporize. Pressure may build up inside the funnel.
An explosion may occur if the tap is not opened regularly for pressure release.
b) Without releasing the pressure, the liquid in the separating funnel will not drain out of the
funnel.
c) The product may not separate out as crystals if too much solvent is used.
22 —
Suggested answers to in-text activities and unit-end exercises
Topic 8 Unit 32
14
© Jing Kung. All rights reserved.