Download 1.1 Chemicals in everyday life

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Chapter 1 answers
Chapter 1 Lifestyle chemistry
1.1 Chemicals in everyday life
Questions
1
Chemical substances applied to the skin may harm the skin if they have properties
that are different from those of the skin. They may react with normal substances
within the skin.
2
a
Butter is a liquid-in-liquid colloid. It is therefore an emulsion—a water-in oil
emulsion.
b
Milk is a liquid-in-liquid colloid and therefore an emulsion—an oil-in-water
emulsion.
c
Toothpaste is a solid-in-liquid colloid.
3
Detergent is a surfactant. Surfactants improve the ‘wetting’ power of water.
4
A surfactant molecule has a hydrophilic (water-attracting) head and a lipophilic
(oil- or fat-attracting) end. This structure allows a surfactant to reduce the surface
tension of water by breaking up water’s ‘skin-like’ surface. The surfactant is able to
dissolve in both fat and water.
5
A colloid contains particles that are evenly distributed throughout the mixture (they
are homogeneous). Therefore the mixture can be evenly spread over the skin.
6
Property
Solution
Colloid
Suspension
Particle size
smallest
intermediate
large
Distribution of
particles in
medium
homogeneous
homogeneous
uneven, nonhomogeneous
Particle settling
particles remain in
solution indefinitely
particles remain in
solutions for long
periods of time
particles settle over
time
Effect of filtering
particles cannot be
filtered
particles cannot be
filtered
particles can be
filtered
Effect on light
beam
light beam is not
visible
scatters light—light
beam is visible
scatters light
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Chapter 1 answers
Further questions
1
Individual student response.
2
3
Laundry detergents work by allowing the water to ‘wet’ fabric easily, by reducing
the surface tension of the water. Dishwashing detergents contain surfactants whose
hydrophobic ends attach to grease and whose hydrophilic ends allow and oil-inwater emulsion for form.
4
Individual student response.
5
Mercury has a much greater surface tension than water. The forces of cohesion
(holding mercury particles together) are much greater than the forces of adhesion
(forces holding mercury particles to the glass container).
1.2 Cleaning products
Questions
1
An emulsion is a colloid containing one liquid evenly dispersed within another
liquid. A suspension is a mixture in which small solid or liquid particles are
suspended in a liquid or gas. The particles of a suspension settle into separate
phases after a short time, whereas an emulsion remains stable for a long period.
2
An emulsifier or emulsifying agent causes particles of one liquid to become evenly
dispersed in a stable suspension in another liquid. This stable suspension is called
an emulsion.
3
Cleaning products contain surfactants so that the cleaning solvent, usually water,
can wet the surface being cleaned. They contain emulsifiers so that the grease and
oil on the surface being cleaned can form an emulsion with the cleaning solvent,
usually water.
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Chapter 1 answers
You could test the electrical conductivity of each moisturiser. The water-based
moisturiser will conduct electricity, while the oil-based moisturiser will not. You
could test both moisturisers with food dyes. The water-based moisturiser will
absorb the dye, while the oil-based moisturiser will not .However, the oil-based
moisturiser will absorb oil-based dyes such as fuchsin. Also, oil-in-water emulsions
feel cool on the skin, but water-in-oil emulsions do not.
5
Biodegradable means ‘able to be broken down readily by natural processes of
microbial decay’. It is important that detergents be biodegradable so that they do not
persist in the environment and pose a hazard to living things.
6
A soap is made by a reaction between fat and alkali in a reaction called
saponification. A synthetic detergent is made from petroleum by-products and
contains a different water-attracting end on its molecules.
7
In automatic washing machines, the soap would form an insoluble scum with the
soil during washing. This scum causes discolouration of clothing and may form a
sediment on the washing machine tub..
8
The hydrophobic tails attract each other less strongly than did the water molecules,
reducing surface tension and allowing the water to wet surfaces more effectively.
Further questions
1
a
Cooks prefer a water-in-oil emulsion because the oil wets the waxy surface of
salad vegetables better and more evenly than water does.
2
b
Add a whisked egg yolk and beat in thoroughly.
a
Refer to Figure 1.22 of text (top and middle pictures, p. 23).
b
Refer to Figure 1.22 of text (bottom picture, p. 23).
c
The dirty wash water can be described as an emulsion because the detergent
emulsifies any grease in the water.
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a
Chapter 1 answers
Surfactants lower the surface tension of water, thus allowing it to wet the
surface of the pine needles. The salt water can then penetrate the outer surface
of the needles and alter the salt balance inside the trees, eventually killing them.
b
Modern surfactants are more biodegradable, causing less damage to the
environment.
4
Water striders make use of the fact that water has a high surface tension in order to
walk on the surface of water. Detergents lower the surface tension of the water so
that water striders sink—this would reduce their population. Detergents also
emulsify oils, and this would interfere with the fatty layers of organisms.
5
Lecithin added to cocoa powder helps to form an emulsion when the cocoa is added
to water or milk. The cocoa fats form an emulsion in the water because of the
presence of lecithin, and these cocoa fats provide the flavour that consumers like.
1.3 Cleaning the human body
Questions
1
The skin consists of different kinds of specialised cells grouped together. Each of
these specialised groups of cells is a tissue. The two major tissue types in the skin
are the epidermis and dermis. An organ consists of at least two tissue types working
together for a common purpose, as the epidermis and dermis act together to perform
the major skin functions. Therefore the skin is an organ.
2
Protection, excretion, assists heat regulation, helps provide immunity from
infection.
3
Because it is an acid it must have a pH less than 7.
4
A skin soap is based on soap made from fat and alkali, whereas a skin cleanser
contains synthetic detergents.
5
Refer to Figure 1.34b of text (p.35).
6
Surfactants wet and emulsify greasy soils from the hair and skin.
7
Microflora are any group of microorganisms that inhabit a particular place.
Microflora on the skin can include bacteria, fungi, viruses, protozoa and algae.
8
Normal bacteria and yeasts in the skin digest dead epidermal cells and secrete
substances that maintain the acidity of the skin.
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Chapter 1 answers
Further questions
1
Most of the skin has little moisture available to support microbes. It is slightly
acidic, which inhibits the growth of most microflora. The surface temperature of the
skin (around 33C) is lower than that required by most microbes. Salt in sweat, and
chemicals such as sebum, fatty acids and urea, make the fluid medium of the skin
unsuitable for most microbes. Sweat, like tears and saliva, also contains an
antibacterial enzyme called lysozyme.
2
a
5.61
b
The average pH of the boys’ skin is higher than the average pH of the girls’
skin.
c
There is no obvious explanation. It could be due the differences in hormones.
d
Perform the same experiment with a much larger sample of boys and girls.
e
UV40 would suit the largest number of students in the class in terms of its
average pH values.
3
When on the surface of the skin this bacterium does not cause disease because it is
present in small numbers, does not attack body tissue and does not provoke an
inflammatory response.
1.4 Solvents
Questions
1
water and alcohol
2
Water does not react adversely with the skin or any other substance in cosmetics. It
dissolves a wide range of substances.
3
Alcohol does not change the way that glycerin works, it dissolves glycerin easily
and it evaporates readily leaving an even layer of glycerin on the skin..
4
Individual student response.
5
Individual student response.
6
Solvents should not be able to penetrate the skin because the balance of fluids in the
body would be disturbed.
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Chapter 1 answers
Further questions
1
a
Vitamin C is highly soluble in water. Vitamin A and stearic acid have low
solubility due to fewer polar bonds in their structures.
b
stearic acid
2
Individual student response.
3
If someone swallows kerosene: Reassure the patient, make him or her as
comfortable as possible and ensure airways are not restricted. Do not induce
vomiting. Call the Poisons Information Centre for information—they will instruct
you if it is necessary to take the patient to hospital.
1.5 Routes for administering drugs to the body
Questions
1
2
Function and pH of each part of the digestive system.
Name of part
Function of part
pH range
teeth
Mechanically break down food into small pieces.
n/a
salivary glands
Secrete enzymes to begin the chemical breakdown of
carbohydrates.
6–8
oesophagus
Carries food by peristalsis to the stomach.
stomach
Churns food. Protein and fat digestion begins here with the
aid of enzymes and hydrochloric acid.
1–3
bile
A liquid made in the liver to emulsify fat droplets in the
duodenum.
8–9
small intestine
Enzymes from the pancreas and the small intestine itself
complete digestion. Nutrients and water are absorbed.
7–9
large intestine
Water and minerals are absorbed.
about 7
The solubility of a drug can be different in the stomach from in the small intestine.
A drug may be more soluble in alkaline conditions than it is in acidic conditions, or
vice versa.
3
Drugs are usually absorbed into the bloodstream via the walls of the small intestine
or stomach, or even through the walls of the mouth. Alternate routes include via
hypodermic syringe, where a drug is directly administered to the bloodstream, or
through dermal patches, subdermal implants or nasal sprays.
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Chapter 1 answers
An enteric-coated tablet is a tablet with a special coating, usually cellulose acetate
phthalate, which only dissolves at pH > 5.8. This means that drugs coated with this
material will not dissolve in the strongly acid conditions in the stomach, but will
dissolve in the slightly alkaline small intestine.
5
a
‘Slow release drugs’ means drugs that release their active ingredients over an
extended period of time, usually up to eight hours.
b
They are used in place of normal tablets for conditions that require a constant
level of release of the drug into the bloodstream.
c
The osmotic pump system uses the principle of osmosis to release the drug.
The drug and a water absorbent substance are surrounded by a semipermeable
membrane pierced by small, laser-drilled holes. As water from the digestive
tract is drawn through the membrane, the substance expands, pushing the drug
through the holes.
In diffusion-controlled systems, the drug simply diffuses through a polymer
coating—either a film or a matrix.
In dissolution-controlled systems, the rate of dissolution of the drug is
controlled by slowly soluble polymers or by microencapsulation. Once the
coating is dissolved, the drug becomes available for dissolution. By varying the
thickness of the coat and its composition, the rate of drug release can be
controlled. .
6
Excess water-soluble vitamins are easily flushed out of the body via the kidneys in
urine. Excess fat-soluble vitamins stay in the body much longer, since they remain
dissolved in the fatty parts that are not flushed out by the urinary system, so their
toxic effects are more serious.
7
The breakdown of food in the digestive system.
Food
Type of digestive
enzyme
Where broken down
pH range
required
starch
amylases
mouth
small intestine
7–8
7–9
protein
proteases (pepsin,
trypsin)
stomach
small intestine
1–3
7–9
fat
lipases
stomach
small intestine
1–3
7–9
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Chapter 1 answers
Further questions
1
The parts of the digestive system most important for chemical breakdown of foods
are the mouth, the stomach and the small intestine. The chemical breakdown of
carbohydrates begins in the mouth. The chemical breakdown of fats and proteins
begins in the stomach. The initial breakdown of proteins requires an acidic
environment (low pH). The stomach walls secrete hydrochloric acid to produce this
acidic environment. Chemical digestion is completed in the small intestine. The
pancreas and the walls of the small intestine produce enzymes that help break down
carbohydrates, proteins and fats. The environment in the small intestine is slightly
basic (alkaline).
2
Individual student response.
3
a
Vitamin A has only one C–O–H group. The rest of the molecule is large and
non-polar. Vitamin C has many C–O–H groups providing many sites for
attraction to water molecules.
b
The C–N–H group is polar and will be attracted to water molecules.
c
If there are a large number of polar bonds in the molecules of a vitamin then it
is likely to be soluble in water
4
Vitamin D appears to be the most dangerous as it is capable of causing death in
some cases. The toxic effects of vitamin D include kidney damage, lethargy,
vomiting, diarrhoea, loss of appetite, hypertension and excess urine production.
Exam-style questions
1
D
2
B
3
D
4
A
5
B
6
C
7
B
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Chapter 1 answers
A water-in-oil emulsion gives complete coverage of the skin with an oily layer
containing the active sunscreen agent. An oil-in-water emulsion would not be
suitable because the water medium would evaporate quickly, leaving areas of the
skin without complete coverage.
9
a
A highly acidic substance will have a pH near 1. Neutral substances have a pH
of 7. Strongly alkaline substances have pH values close to 14.
b
Choose which different parts of the skin will be tested, making sure that the
sites include both dry and moist areas of the skin such as the back of the hand
and under the arms. Place a piece of pH paper dipped in distilled water on each
site for one minute. Repeat each test twice. Repeat the test on a number of
people.
10 The oil produced by sebaceous glands consist of fatty acids and other acids
produced by bacteria. The bacteria break down the dead lining the walls of the
glands and secrete substances that help to maintain the skin’s pH of about 5.5. The
sweat glands also secrete fatty acids that contribute to the maintenance of the skin’s
pH.
11 a
Wets the surface of the skin and emulsifies any greasy soil on the skin.
b
Prevents deterioration of skin cleansers by destroying microbes.
c
Makes the skin feel soft.
12 a
Microflora are microbes that normally occupy a certain habitat, such as the
skin.
b
The normal microflora on the dry parts of the skin include Staphylococcus
epidermidis and Corynebacterium, which help to maintain the pH of the skin
and ward off potentially harmful microbes. Bacteria called Propionibacterium
acnes inhabit the sebaceous glands. While these bacteria help break down dead
skin cells and produce acids to keep pH in balance, they can also cause an
inflammatory response and lead to acne.
13 a
Alcohol gives a cooling effect as it evaporates quickly from the skin. Also, it is
a mild antiseptic.
b
Glycerin retains moisture and makes the skin feel soft.
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14 a
Chapter 1 answers
The drug reaches the affected cells through the bloodstream, after passing
through the digestive system and the walls of the small intestine.
b
Because this drug passes through the digestive system before it reaches the
blood, it can only remain available for as long as it takes to pass through the
small intestine. This is usually 4 to 6 hours.
c
Only soluble drugs can pass through the walls of the digestive system into the
bloodstream to reach the part of the body where they are needed. A drug may
be soluble in water or fat.
15 a
b
It is fat-soluble.
Vitamin C is water-soluble and therefore easily flushed out of the body when
taken in large doses.
16 a
b
1 to 3.
Some materials coating the drug or the drug itself may be insoluble in the
acidic conditions in the stomach. Other drugs may dissolve quickly in acidic
conditions.
c
To avoid dissolving in the stomach, a drug can be coated with an enteric
coating that does not dissolve in acidic conditions.
d
The stomach is acidic with a pH range of 1 to 3 while the duodenum is slightly
alkaline. The enzymes in the stomach are different from those in the
duodenum.
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