HSS2ch1

Heinemann Senior Science 2 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, non-homogeneous

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

Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 1


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-in-

water emulsion for form.


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.



4 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.

b Add a whisked egg yolk and beat in thoroughly.

2 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.

3 a 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.



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 33C) 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..



6 Solvents should not be able to penetrate the skin because the balance of fluids in

the body would be disturbed.



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


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 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

2 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.



4 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 mouthsmall intestine

7–87–9

protein proteases (pepsin, trypsin)

stomachsmall intestine

1–37–9

fat lipases stomachsmall intestine

1–37–9



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).


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

8 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.

14 a 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 It is fat-soluble.

b Vitamin C is water-soluble and therefore easily flushed out of the body when

taken in large doses.

16 a 1 to 3.

b 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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