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Suggested answers to in
-
text activities and unit
-
end exercises


1

©

Jing Kung
.
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Topic
8 Unit 33



Suggested answers to in
-
text activities and unit
-
end exercises

Topic
8

Unit
33


I
n
-
text activities

Internet Search & Presentation (page
207
)

The aspirin story

The history of aspirin and other medicines dealing with pain, fever or inflammation reveals many
interesting points about scientific methodology and the interaction of people and society with
technology. One overriding theme that emerges when looking at the development of medicines is
the importance of sharing information and cooperation in research.
Time and again discoveries in
one part of the world have been published, but not developed fully until another person reads and
uses the information in another time and place.

The textbook gives some detail of the history of the development of aspirin, but

it is intended that
students find out more than what has been given to them.


Conditions that aspirin helps to relieve or cure

At over
-
the
-
counter dosage (one or two grams), it relieves fever and minor aches and pains. At
dosages three or four times highe
r, available by prescription only, it reduces swelling and is used to
treat gout, rheumatoid arthritis, and inflammatory ailments. Many people take low dosages (below
100 milligrams) daily for preventing recurrent stroke or heart attack. Recent studies fou
nd it
effective in reducing risks for colon and breast cancers. Evidence is accumulating for similar effects
in Alzheimer and other diseases.

However, aspirin can irritate the stomach and in some cases cause ulcer and internal bleeding.
Alternative treatme
nts for pain relief are available: paracetamol and ibuprofen.


Making aspirin soluble

One problem with aspirin is that it is not particularly soluble in cold, or even warm, water (e.g. 36
°C


the temperature of the human body).

A medicine tablet works far

better if it is water
-
soluble, because it then enters the bloodstream more
rapidly. One way of making the aspirin ‘soluble’ is to convert it to one of its salts, e.g. the sodium
salt. As this product is ionic, it would be much more water
-
soluble than the
parent covalent acid


aspirin itself.


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Clinical trials

A new medicine has to demonstrate its safety, quality and efficacy through a series of rigorous
clinical trials in order to obtain a licence and be available to the general public.

Clinical trials ar
e conducted in phases. The trials at each phase have a different purpose and help
scientists answer different questions.



In Phase I trials, researchers test an experimental drug in a small group of people (20


80) for
the first time to evaluate its safe
ty, determine a safe dosage range, and identify side effects.



In Phase II trials, the experimental study drug is given to a larger group of people (100


300) to
see if it is effective and to further evaluate its safety.



In Phase III trials, the experi
mental study drug is given to large groups of people (1 000


3 000)
to confirm its effectiveness, monitor side effects, compare it with commonly used treatments,
and collect information that will allow the experimental drug to be used safely.



In Phase I
V trials, post marketing studies delineate additional information including the drug’s
risks, benefits, and optimal use.


References:

http://www.creatingtechnology.org/biomed/aspirin.htm

http://docbrown.info/page04/OilProducts15.htm

http://www.abpi.org.uk/
/publications/briefings/clinical_brief.pdf

http://clinicaltrials.gov/ct2/info/understand


Internet Search & Presentation (page
215
)

Soap
-
making by ancient people

Soap making is one of the oldest known organic chemical reactions. Soaps are formed by the
rea
ction of fats or oils with an alkali. It is possible that the process could have been discovered in
prehistoric times when animal fat from cooking meat dripped onto wood ash (which is alkaline)
producing a crude soap. Archaeologists once found evidence tha
t the Babylonians were making
soap around 3000 BC. Soap making was probably introduced to Europe by the Phoenicians around
600 BC.

The Romans also produced soap. The word soap in many languages is derived from a famous
Roman legend. According to this legen
d women who washed clothes in the stream below Sapo Hill
noticed how much easier they were to clean than in other streams. It seemed that the ashes and fats
from sacrificial fires in temples on Sapo Hill mixed together to produce soap which was washed
down

from the hill. A soap
-
making factory, complete with soap moulds and bars of soap, was
discovered in the ruins of Pompeii. With the fall of the Roman Empire, soap making declined and
soap was used mostly for cleaning clothes and textiles rather than for pe
rsonal bathing.


Commercial production of soap in Europe

Soapmakers’ guilds began to spring up in Europe during the seventeenth century. Southern
European countries, such as Italy, Spain, and France were early production centers for soap.

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Topic
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The English began

soapcrafting during the twelfth century. Unfortunately, soap was heavily taxed
as a luxury item, and so it was only readily available to the rich. In 1853, when the English soap tax
was repealed, a boom in the soap trade coincided with a change in the soc
ial attitudes toward
personal cleanliness.

In America, soap was made by women producing it out of their homes seasonally. The commercial
production of soap did not start until the early 1600s when enterprising soapmakers from England
began arriving in the
New World.


Scientific advancements and soap
-
making

Scientific advancements that affected the soapmaking trade began with Nicholas Leblanc, a French
chemist who patented a process for making an alkali from common salt in 1791. His process
allowed for the i
nexpensive production of soda ash.

In the early 1800s, Michel Chevreul's significant discoveries about the relationship of fats, glycerine,
and fatty acids laid the groundwork for the chemistry of soaps and fats.

During the mid 1800s, Belgian chemist Ernes
t Solvay discovered the ammonia process that
improved the methods for extracting soda ash from common salt. This increased the availability and
quality of soda ash for soap making.

As a result of the scientific achievements, soap became a popular and easy
-
to
-
obtain commodity.


Production of soapless detergents

Soapless detergents use materials called surfactants which dissolve greases; detergent effects of
certain synthetic surfactants were first noted in 1913 by A Reychler, a Belgian chemist. During
World
War I the Germans used soapless detergents as an alternative to soap but after that war their
uses were largely confined to industrial processes.

After World War II the U.S. aviation fuel plants changed over to making tetrapropene, used in
household deterg
ents, causing a fast growth of household use in the late 1940s. The first product
was a ‘soapless shampoo’. Up to the 1960s they were more expensive than traditional soaps but
they could be used with hard or soft water equally well.

In the late 1960s biolo
gical detergents, containing enzymes and better suited to dissolve protein
stains such as egg stains, were introduced in the U.S..


References:

http://inventors.about.com/library/inventors/blsoap.htm

http://www.harvestsoaps.com/history_of_soap.htm

http://w
ww.soapmakingfun.com/making
-
homemade
-
soap/history
-
of
-
soap
-
making.shtml

http://www.sappohill.com/soaphistory.html

http://www.worldlingo.com/ma/enwiki/en/Detergent

http://www.igg.org.uk/gansg/12
-
linind/soap.htm


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Topic
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Checkpoint (page 225)

1

CH
3
(CH
2
)
14
CH
2


is a no
n
-
polar group which can dissolve in grease.


is a polar group which can dissolve in water.

2

a)

Detergent I

b)


c)

Before shaking an oil
-
water mixture, the hydrocarbon ‘tails’ of detergent particles are
soluble in the oil and the anionic ‘heads’ are solu
ble in the water.

Upon shaking, oil droplets form. Each droplet is surrounded by detergent particles with the
anionic ‘heads’ in the water.

Repulsion between the anionic heads prevents the oil droplets from coming together again.
Thus, the oil droplets rem
ain suspended in the water. An emulsion is formed.

d)

Detergent I functions well in hard water.

When detergent II is added to hard water, scum forms.

A lot of the detergent is needed to get a lather.

e)

Not suitable

Sea water contains a lot of metal ions,
such as magnesium ions and calcium ions.

Detergent II will react with the metal ions to form scum and hence reduce the effectiveness
of the detergent.


Checkpoint (page 236)

1


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Topic
8 Unit 33



2

a)


b)

Carboxyl group; hydroxyl group


Checkpoint (page 244)

1

a)

Ester fun
ctional group; carbon
-
carbon double bond

b)


c)

X is formed from an unsaturated carboxylic acid.

It is a liquid at room temperature as its molecules cannot pack together closely due to the
presence of
cis

double bonds.

2

a)

First gently heat, while stirri
ng, a mixture of fat and concentrated sodium hydroxide solution
for about 20 minutes. Most of the soap formed dissolves in the reaction mixture.

Then add concentrated sodium chloride solution to the mixture. The soap separates from the
solution and floats
on the surface.

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Topic
8 Unit 33



Obtain the soap by filtration. Then wash the soap with a little distilled water and allow to
dry.

b)


c)

Saponification


Checkpoint (page 249)

a)

Amine functional group, carboxyl group, amide functional group, ester functional group

b)



Internet Search & Presentation (page
249
)

Saccharin

Saccharin was discovered over a century ago and has been used as a non
-
caloric sweetener in foods
and beverages for more than 100 years. Saccharin contributes no calories to the diet because it is not
met
abolized by the human body. (It is excreted in the same form as ingested.)



Uses of saccharin

Saccharin is useful for people trying to control their weight. Saccharin may assist in weight
management, control of blood glucose and prevention of dental cari
es.

Saccharin is appropriate for medical and nutrition therapy for people with diabetes, and dietetic
professionals may incorporate saccharin into the individualized meal plans of their patients who
have diabetes.


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References:

http://www.saccharin.org/pdf/
sach_broch_final_406.pdf

http://chemistry.about.com/od/factsstructures/ig/Chemical
-
Structures
---
S/Saccharin.htm


Sucrose

Sucrose or table sugar is obtained from sugar cane or sugar beets.

Sucrose is made from glucose and fructose units. The glucose and fru
ctose units are joined by a
glycosidic linkage.



Uses of sucrose

Sucrose and its co
-
products lend themselves to possibilities in many areas:



fine chemicals;



pharmaceuticals;



polymers;



building and structural materials;



fermentation or enzyme su
bstrate for chemicals production;



new food products and sweeteners;



making biodiesel / ethanol;



transformation of cane or beet plant to make other products.


References:

http://www.spriinc.org/buton10bftpp.html

http://www.elmhurst.edu/~chm/vchembook/
546sucrose.html


Cellulose

Cellulose is a natural polymer of the β
-
glucose monomer. Two b
-
glucose monomer molecules can
link together via an oxygen atom at the first carbon atom (C1) of one unit and the fourth carbon
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atom (C4) of the next. A water molecule

is released. This is a condensation reaction. The link
between the two glucose units is called a glycosidic linkage.



Uses of cellulose

Cellulose has been used to make paper since the Chinese first invented the process around AD 100.
Cellulose is separa
ted from wood by a pulping process that grinds woodchips under flowing water.
The pulp that remains is then washed, bleached and poured over a vibrating mesh. When the water
finally drains from the pulp, what remains is an interlocking web of fibres that,
when dried, pressed,
and smoothed, becomes a sheet of paper.

Cellulose is the major constituent of textiles made from cotton, linen and other plant fibres.

Cellulose can also be processed and chemically modified to make plastics, photographic film, and
ray
on. Cellulose derivatives can be used as adhesives, explosives, thickening agents in food, and
moisture
-
proof coatings. Historically, cellulose made some of the first synthetic polymers like
cellulose nitrate, cellulose acetate, ethyl cellulose and rayon.


References:

http://www.scienceclarified.com/Ca
-
Ch/Cellulose.html

http://en.wikipedia.org/wiki/Cellulose

http://web1.caryacademy.org/chemistry/rushin/StudentProjects/CompoundWebSites/2000/Cellulose
/uses.htm


Starch

The main sources of starch are the cereal

crops, rice, maize, wheat and the root crop potatoes.

Starch is composed of a mixture of two substances: amylose, an essentially linear polysaccharide,
and amylopectin, a highly branched polysaccharide. Both forms of starch are polymers of a
-
glucose.
Natu
ral starches contain 10


20% amylose and 80


90% amylopectin.

Amylose typically consists of more than 1 000 glucose units link together via oxygen atoms
between the first carbon atom (C1) of one unit and the fourth carbon atom (C4) of the next. The link
between glucose units is called a glycosidic linkage.

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Chains of glucose units with such glycosidic linkages tend to assume a helical arrangement.

Amylopectin has a structure similar to that of amylose, with the exception that in amylopectin the
chains ar
e branched. Branching takes place between C6 of one glucose unit and C1 of another and
occurs at intervals of 20


25 glucose units.


These two molecules are assembled together to form a semi
-
crystalline starch granule. The granule
also contains small amo
unts of lipid and phosphate. The exact proportions of these molecules and
the size of the granule vary between species.


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Examples of use of starch

Food and
drinks

Animal
feed

Agriculture

Plastic

Pharmacy

Building

Textile

Paper

Various

mayonnaise

pellets

s
eed coating

biodegradable
plastic

tablets

mineral
fibre

warp

corrugated
board

oil
drilling

baby food

by
-
product

fertilizer


dusting
powder

gypsum
board

fabrics

cardboard

water
treatment

bread





concrete

yarns

paper

glue

soft drinks









meat
produ
cts









confectionery









Source: International Starch Institute, Aarhus, Denmark


References:

http://www.starch.dk/

http://jxb.oxfordjournals.org/cgi/content/full/54/382/451


Cholesterol

Cholesterol is a waxy, fat
-
like compound that belongs to a

major class of lipids called steroids. It's
found in many foods, in the bloodstream and in all the body’s cells.


Cholesterol comes from two sources: the body and food. The liver and other cells in the body make
about 75% of blood cholesterol. The other
25% comes from food.


Functions of cholesterol

Cholesterol is essential for



formation and maintenance of cell membranes (helps the cell to resist changes in temperature
and protects and insulates nerve fibres);



formation of sex hormones;



production o
f bile salts, which help to digest food;



conversion into vitamin D in the skin when exposed to sunlight.


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Good’ and ‘bad’ cholesterol

Cholesterol cannot dissolve in the blood. It has to be transported to and from the cells by carriers
called lipoprotein
s. Lipoproteins consist of protein, cholesterol, triglycerides and phospholipids.
The density of these lipoproteins is determined by the amount of protein in the molecule. The terms
‘good’ and ‘bad’ cholesterol refer to high density lipoproteins (HDL) and
low density lipoproteins
(LDL) respectively.

When too much LDL (bad) cholesterol circulates in the blood, it can slowly build up in the inner
walls of the arteries that feed the heart and brain. Together with other substances, it can form plaque,
a thick,
hard deposit that can narrow the arteries and make them less flexible. This condition is
known as atherosclerosis. If a clot forms and blocks a narrowed artery, heart attack or stroke can
result.

About one
-
fourth to one
-
third of blood cholesterol is carrie
d by high
-
density lipoprotein (HDL).
HDL cholesterol is known as ‘good’ cholesterol, because high levels of HDL seem to protect
against heart attack. Low levels of HDL also increase the risk of heart disease.

Medical experts think that HDL tends to carry c
holesterol away from the arteries and back to the
liver. Some experts believe that HDL removes excess cholesterol from arterial plaque, slowing its
buildup.


References:

http://health.howstuffworks.com/cholesterol1.htm

http://www.americanheart.org/presente
r.jhtml?identifier=512

http://www.scientificpsychic.com/health/lipoproteins
-
LDL
-
HDL.html


Insulin

Glucose provides energy to all of the cells in the body. The cells take in glucose from the blood and
break it down for energy. The glucose in the blood comes

from food.

When a person eats food, glucose gets absorbed from the intestines and distributed by the
bloodstream to all of the cells in the body. The body tries to keep a constant supply of glucose for
the cells by maintaining a constant glucose concentra
tion in the blood. So, when there is an
oversupply of glucose, the body stores the excess in the liver and muscles by making glycogen, long
chains of glucose. When glucose is in short supply, the body mobilizes glucose from stored
glycogen and / or stimula
tes the person to eat food.

To maintain a constant blood
-
glucose level, the body relies on two hormones produced in the
pancreas that have opposite actions: insulin and glucagon.

Insulin consists of two polypeptide chains, an A chain and a B chain, joined
together by disulphide
bonds. The smaller of the two chains is referred to as the A chain and is 21 amino acids long in
humans. The second chain is referred to as the B chain and is 30 amino acids long in humans.

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Source: http://www.chemistryexplained.com
/Hy
-
Kr/Insulin.html


Functions of insulin

Insulin is required by almost all of the body’s cells, but its major targets are liver cells, fat cells and
muscle cells. For these cells, insulin does the following:



stimulates the liver and muscle cells to stor
e glucose in glycogen;



stimulates the fat cells to form fats from fatty acids and glycerol;



stimulates the liver and muscle cells to make proteins from amino acids;



inhibits the liver and kidney cells from making glucose from intermediate compounds o
f
metabolic pathways (gluconeogenesis).


Diabetes

Diabetes is classified into three types: Type 1, Type 2 and gestational diabetes.

Type 1 is caused by a lack of insulin. This type is found in 5


10% of diabetics and usually occurs
in children or adolesce
nts.

Type 2 occurs when the body does not respond or cannot use its own insulin. Type 2 occurs in 90


95% of diabetics and usually occurs in adults over the age of 40, most often between the ages of 50
and 60.

Gestational diabetes can occur in some pregna
nt women and is similar to Type 2 diabetes. During
pregnancy, several hormones partially block the actions of insulin, thereby making the woman less
sensitive to her own insulin.


References:

http://health.howstuffworks.com/diabetes1.htm

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http://www.vivo.co
lostate.edu/hbooks/pathphys/endocrine/pancreas/insulin_struct.html

http://www.providence.edu/chm/kcornely/Case%204_%20The%20structure%20of%20insulin.pdf


Casein

Milk is a complex biological fluid with high amount of proteins, lipid and minerals. The functi
on of
milk is to supply nutrients such as essential amino acids required for the growth of the newborn.

Originally, milk proteins were believed to be a simple homogeneous protein, but about a century or
more ago, milk proteins were divided into two broad c
lasses. The first fraction, which is about 80%
of the protein in bovine milk, is called casein. The second fraction, which makes up about 20% of
protein, is referred to as whey protein, serum protein or non
-
casein nitrogen.

Casein exists in milk in complex

groups of molecules that are called ‘micelles’.

A typical micelle contains on the order of 10
4

polypeptide chains of four basic types, together with
about 3 x 10
3

microgranules of an amorphous calcium phosphate. The micelles are polydisperse in
size and v
ariable in composition.

Due to the importance of casein and casein micelles for the functional behaviour of dairy products,
the nature and structure of casein micelles have been studied extensively, but the exact structure of
casein micelles is still under

debate.

Various models for casein micelle structure have been proposed. Most of the proposed models fall
into three general categories: coat
-
core, subunit (sub
-
micelles), and internal structure models.


Functions of casein

The casein micelle is an importa
nt and characteristic macromolecular assembly of mammalian
biology, occurring in all milks that have been examined in sufficient detail. Its functions, insofar as
they are known, are to form a coagulum in the stomach of the nursling, allowing the slow rele
ase of
nutrients down the digestive tract, and to act as a means of transporting calcium and phosphate in a
readily assimilable form from mother to young. As well as providing a source of amino acids,
enzymatic cleavage of casein polypeptide chains can pro
duce various types of biologically active
peptides.

Another recent speculation is that casein has a role in protecting the mammary gland against ectopic
calcification, a hazard that is common to all tissue in contact with supersaturated calcium solutions.


References:

http://www.nzic.org.nz/ChemProcesses/dairy/3E.pdf

http://books.google.com.hk/books?id=9H_gemXpEWQC&pg=PA63&lpg=PA63&dq=structure+of
+CASEIN&source=bl&ots=mxmH460AUp&sig=M
-
EfF2UOtYlYE9E6L
-
MUH3YTQzw&hl=zh
-
T
W&ei=KaL8S_T7N4uTkAWGi9iMBw&sa=X&oi=book
_result&ct=result&resnum=10&ved=0CD
cQ6AEwCTge#v=onepage&q=structure%20of%20CASEIN&f=true

http://rdo.psu.ac.th/sjst/journal/27
-
1
-
pdf/19casein
-
micelle.pdf


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Unit
-
end exercises
(pages
255



267
)

Answers for the HKCEE (Paper 1) and HKALE questions are not provi
ded.

1

a)

i)

B

ii)

A

b)


2

When we add a detergent solution to a table cloth stained with grease, the hydrocarbon ‘tails’ of
the detergent particles dissolve in the grease. The anionic ‘heads’ of the detergent particles are
insoluble in the grease and rem
ain outside.

The surrounding water molecules attract the anionic ‘heads’ and lift the grease off the surface.

By stirring, the grease (which carries the dirt particles) breaks up into tiny droplets suspended in
the water. These tiny droplets cannot come to
gether again due to the repulsion between the
anionic ‘heads’ of detergent particles on their surfaces. An emulsion forms.

Rinsing washes away the greasy suspension, and leaves the surface clean.

3

a)

A

hexane
-
1,6
-
dioic acid

B

hexane
-
1,6
-
diamine

b)

Condens
ation polymerization

c)


4

a)


b)

i)


ii)

Condensation polymerization

c)

Fibres used to make clothes

Bottles for carbonated drinks

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d)

By the hydrolysis of the ester linkage by enzymes or microorganisms

5

Carbonyl group

Hydroxyl group

6

B

7

B

8

B

9

B

10

B

(1)

X is a condensation polymer.

(2)

X is formed from the condensation polymerization of two different monomers.


11



12



13



14

a)

Little / no lather

Scum

b)

Add dilute nitric acid followed by silver nitrate solution.

A

white precipitate forms.

c)

T
here are several ions that would give a colour flame.

15

a)

Ester functional group; carbon
-
carbon double bond

b)

i)

Saponification

ii)

First gently heat, while stirring, a mixture of vegetable oil and concentrated sodium
hydroxide solution for about 20 min
utes. Most of the soap formed dissolves in the
reaction mixture.

Then add concentrated sodium chloride solution to the mixture. The soap separates from
the solution and floats on the surface.

Obtain the soap by filtration. Then wash the soap with a litt
le
distilled water and allow to
dry.

c)

Hydrogenation of vegetable oils

d)

Hydrocarbons from petroleum, concentrated sulphuric acid and sodium hydroxide

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e)

Bacteria use up oxygen in the water during the decomposition of detergents. This makes the
water of som
e streams, rivers and seas smell badly due to oxygen depletion.

16

a)


b)

When the soap is added to hard water, scum forms.

The scum forms because the calcium and magnesium ions in hard water react with the soap,
giving an insoluble product that floats on

the water.


c)

Washing soda reacts with calcium ions and magnesium ions in hard water to form insoluble
carbonates, thus removing the hardness of water.

17

a)

i)

Carbon and hydrogen

ii)


iii)

Permanent dipole
-
permanent dipole attractions

iv)

Reflux glyc
erol and carboxylic acid in the presence of concentrated sulphuric acid.

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b)

i)

Hydrogen bonding is the attraction between the hydrogen atom attached to an oxygen
atom and the lone pair on another oxygen atom.


ii)

Glycerol is soluble in water because its
molecules can form many hydrogen bonds with
water molecules.

The boiling point of a compound depends on the strength of its intermolecular
attractions.

Strong hydrogen bonds exist in glycerol.

Hence a lot of heat is needed to separate the glycerol molecule
s during boiling.

Thus glycerol has a relatively high boiling point.

c)

i)

Propene

ii)

Petroleum

iii)

Substitution

iv)

Sodium hydroxide solution

v)


vi)

Number of moles of compound A =




= 0.71 mol


Theoretical
yield

of glyce
rol = 0.71 mol
x

92.0 g mol

1


= 65 g



Percentage
yield

of
glycerol

=

x

100%


= 3%

18

a)

Monomer molecules join together repeatedly to form polymer molecules.

Small water molecules are formed during the reaction.

2 g

65

g


30 g

42

g

mol

1


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Topic
8 Unit 33



b)


c)


19

a)


b)

i)


(any one of the hydrogen bonds is acceptable)

ii)

Strong hydrogen bonds hold the polymer chains and water molecules together.

c)

i)

Permanent dipole
-
permanent dipole attractions exist between chains of the polymer
derived from compound A while

hydrogen bonds exist between chains of the polymer
derived from compound B.

Hence chains of the polymer derived from compound A can slide past one another more
easily.

Thus the polymer is more flexible.

ii)


iii)

No

The polymer does not contain carbon
-
ca
rbon double bond.

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Topic
8 Unit 33



20

a)

Any one of the following:



To improve the quality.



To reduce cost.



The demand is greater than the nature can supply.

b)


c)

i)

butane
-
1,4
-
diamine

ii)

Any two of the following:



Lower melting point



Lower strength



Lower rig
idity

d)

i)

Number of repeating units =





= 151

ii)

Amide functional group

iii)

The number of hydrogen bonds per unit length of polymer chain of Stanyl is greater than
that of nylon
-
6,6.

Hence more heat is needed to overcome
the forces between the polymer chains of Stanyl,
enabling the chains to move over one another.

e)

i)


3
x

10
4

198.0

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Topic
8 Unit 33



ii)


(any one of the hydrogen bonds is acceptable)

21

a)

Number of moles of CO
2

produced by 0.10 g of Z =


=

2.2
x

10

3

mol

Mass

of C in 0.10 g of Z = 2.2
x

10

3

mol
x

12.0 g mol

1


=

0.026 g

Mass

of H in 0.10 g of Z = 0.020 g
x



=

2.2
x

10

3

g

Mass

of O in 0.10 g of Z = (0.10


0.026


2.2
x

10

3
) g


=

0.072 g




the empirical formula of Z is CHO
2
.

2.0 g mol

1

18.0 g mol

1

53 cm
3

24 000 cm
3

mol

1

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Topic
8 Unit 33



b)

Let (CHO
2
)
n

be the molecular formula of Z.

Molar mass of Z

=
n
(12.0 + 1.0 + 2 x 16.0) g mol

1


= 90.0 g mol

1

n

= 2



the molecular formula of Z is C
2
H
2
O
4
.

c)

Number of moles of 0.900 g of Z =



= 0.0100 mol


Number

of moles of NaOH required for complete neutralization

= 1.00 mol dm

3

x


dm
3

= 0.0200 mol

0.0100

m
ole of Z requires 0.0200 mole of NaOH for complete neutralization.


i.e.

1 mole of Z requires 2 moles of NaOH for complete neutralization.

It

can be deduced that Z should contain two

COOH groups.


the structural formula of Z is

.

d)

W

CH
2
=CH
2

X

BrCH
2
CH
2
B
r

Y

HOCH
2
CH
2
OH

e)

C
20
H
42



C
18
H
38

+ C
2
H
4

22


23



24



25





20.0

1

000

0.900 g

90.0 g mol

1