Heinemann Senior Science 2Chapter 1 Answers

Heinemann Senior Science 2Chapter 1 answers

Chapter 1 Lifestyle chemistry

1.1 Chemicals in everyday life

Questions

1Chemical 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.

2aButter is a liquid-in-liquid colloid. It is therefore an emulsion—a water-in oil emulsion.

bMilk is a liquid-in-liquid colloid and therefore an emulsion—an oil-in-water emulsion.

cToothpaste is a solid-in-liquid colloid.

3Detergent is a surfactant. Surfactants improve the ‘wetting’ power of water.

4A 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.

5A colloid contains particles that are evenly distributed throughout the mixture (they are homogeneous). Therefore the mixture can be evenly spread over the skin.

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

Further questions

1Individual student response.

3Laundry 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.

4Individual student response.

5Mercury 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

1An 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.

2An emulsifieror 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.

3Cleaning 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.

4You 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.

5Biodegradable 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.

6A 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.

7In 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..

8The 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

1aCooks prefer a water-in-oil emulsion because the oil wets the waxy surface of salad vegetables better and more evenly than water does.

bAdd a whisked egg yolk and beat in thoroughly.

2aRefer to Figure 1.22 of text (top and middle pictures, p. 23).

bRefer to Figure 1.22 of text (bottom picture, p. 23).

cThe dirty wash water can be described as an emulsion because the detergent emulsifies any grease in the water.

3aSurfactants 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.

bModern surfactants are more biodegradable, causing less damage to the environment.

4Water 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.

5Lecithin 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

1The 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.

2Protection, excretion, assists heat regulation, helps provide immunity from infection.

3Because it is an acid it must have a pH less than 7.

4A skin soap is based on soap made from fat and alkali, whereas a skin cleanser contains synthetic detergents.

5Refer to Figure 1.34b of text (p.35).

6Surfactants wet and emulsify greasy soils from the hair and skin.

7Microflora are any group of microorganisms that inhabit a particular place. Microflora on the skin can include bacteria, fungi, viruses, protozoa and algae.

8Normal bacteria and yeasts in the skin digest dead epidermal cells and secrete substances that maintain the acidity of the skin.

Further questions

1Most 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.

2a5.61

bThe average pH of the boys’ skin is higher than the average pH of the girls’ skin.

cThere is no obvious explanation. It could be due the differences in hormones.

dPerform the same experiment with a much larger sample of boys and girls.

eUV40 would suit the largest number of students in the class in terms of its average pH values.

3When 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

1water and alcohol

2Water does not react adversely with the skin or any other substance in cosmetics. It dissolves a wide range of substances.

3Alcohol 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..

4Individual student response.

5Individual student response.

6Solvents should not be able to penetrate the skin because the balance of fluids in the body would be disturbed.

Further questions

1aVitamin C is highly soluble in water. Vitamin A and stearic acid have low solubility due to fewer polar bonds in their structures.

bstearic acid

2Individual student response.

3If 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

1Function 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

2The 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.

3Drugs 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.

4An 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.

5a‘Slow release drugs’ means drugs that release their active ingredients over an extended period of time, usually up to eight hours.

bThey are used in place of normal tablets for conditions that require a constant level of release of the drug into the bloodstream.

cThe 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. .

6Excess 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.

7The 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

Further questions

1The 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).

2Individual student response.

3aVitamin 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.

bThe C–N–H group is polar and will be attracted to water molecules.

cIf there are a large number of polar bonds in the molecules of a vitamin then it is likely to be soluble in water

4Vitamin 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

8A 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.

9aA 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.

bChoose 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.

10The 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.

11aWets the surface of the skin and emulsifies any greasy soil on the skin.

bPrevents deterioration of skin cleansers by destroying microbes.

cMakes the skin feel soft.

12aMicroflora are microbes that normally occupy a certain habitat, such as the skin.

bThe 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.

13aAlcohol gives a cooling effect as it evaporates quickly from the skin. Also, it is a mild antiseptic.

bGlycerin retains moisture and makes the skin feel soft.

14aThe drug reaches the affected cells through the bloodstream, after passing through the digestive system and the walls of the small intestine.

bBecause 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.

cOnly 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.

15aIt is fat-soluble.

bVitamin C is water-soluble and therefore easily flushed out of the body when taken in large doses.

16a1 to 3.

bSome 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.

cTo avoid dissolving in the stomach, a drug can be coated with an enteric coating that does not dissolve in acidic conditions.

dThe 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.