Chapter 14 Chemicals for Consumers

Concept Map

14.1 Soap

1. Soap is water soluble sodium or potassium salts of fatty acids which consist of 12 to 18 carbon atoms per molecule.

2. Soap is manufactured by heating animal fats or vegetable oils with concentrated sodium hydroxide.

3. Animal fats or vegetable oils are natural esters from fatty acids and glycerol.

4. The general formula of soap is RCOONa where R is a long-chained alkyl group.

5. Some examples of soap is shown in the table below.

Soap Fatty acid Raw material

Sodium oleate Oleic acid Olive oil

Sodium palmitate Palmitic acid Palm oil

Sodium laurate Lauric acid Coconut oil

6. The process of making soap is called saponification. It involves the hydrolysis of fats or oils catalysed by concentrated alkali.

boil

Fats + NaOH ¾® soap + glycerol

boil

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Chemicals for Consumers

Soap Detergent

Saponification

Soap molecule:Hydrophobic endHydrophilic end

Cleansing action

Effect in hard water

Natural and synthetic

Detergent molecules:alkyl sulphates and alkylbenzene sulphonates

Cleansing action

Effect in hard water

Medicine

Traditional and modern

Food additives

Plants and herbsAnalgesicAntibioticPsychotherapeutic drugsHormones and drugs

FunctionsSide effects Correct usage

PerservativesAntioxidantsFlavouring agentsColouring agents

FunctionsSide effectsUses

Oils + NaOH ¾® soap + glycerol

14.2 The Cleansing Action of Soap and Its Effectiveness

1. Cleansing is ineffective if only water is used because water, being a polar solvent, cannot dissolve oil or grease which are found in dirt.

2. A cleansing agent is required to

(a) aid water in wetting the surface of the object to be cleaned by reducing the surface tension of water,

(b) isolate or separate the oil or grease from the surface of the object to be cleaned,

(c) emulsify the dirt in water so that the dirt can be easily expelled.

3. When soap dissolves in water, the soap molecule is ionized to form cations and anions of soap.

CH3(CH2)14COONa(s) ® CH3(CH2)14COO– (aq) + Na + (aq)

4. The cleansing action of soap is explained by the properties of the structure of the anions of soap:

(a) The anion of soap has a structure that consists of two components: the long-chained hydrocarbon which is hydrophobic and the negative end

which is hydrophilic.

(b) The hydrophobic hydrocarbon is covalent in nature which dissolves in grease but not in water, whereas the hydrophilic component is ionic

and dissolves in water but not in grease.

(c) Both of these properties of the anion of soap enable the soap to clean greasy stains effectively.

6. The cleansing action of soap:

14.3 Detergent

1. Detergent is the sodium salt of organic acid such as sulphonic acid.

2. Natural detergent is made from animal or vegetable oil while synthetic detergent is normally made from petroleum.

3. Commercial detergents are usually sodium alkyl sulphates and sodium alkylbenzene sulphonates.

4. When detergent dissolves in water, it is ionized to sodium cations and anions of the detergent.

5. The cleansing action of the detergent can be explained by using the structural properties of its anions.

(a) The anions of the detergent consist of two components: the hydrophobic and the hydrophilic components.

(b) The hydrophobic component dissolves in grease but not in water while the hydrophilic component dissolves in water but not

in grease.

6. Advantages and disadvantages of soap:

Advantages Disadvantages

(a) Soap is a biodegradable substance which can be

decomposed by bacteria. Therefore soap does not pose a

threat to the environment.

(b) Soap can only clean effective in pure water which

does not contain dissolved calcium or magnesium ions.

(c) Soap is also ineffective in acidic water. This is

because the hydrogen ions can react with the anions of

soap such as stearate to form fatty acid molecules.

(a) Soap is ineffective in hard water which contains

dissolved calcium or magnesium ions or other minerals.

(b) The calcium and magnesium which are present in

hard water can combine with the anions of soap to form a

white precipitate called scum.

(c) The scum formed will float on the surface of the

water causing the cleansing action to start only after all

the calcium and magnesium ions in the hard water react

completely with the anions of soap.

(d) The scum formed will also stick onto the cloth and

hard to remove.

7. Advantages and disadvantages of detergent:

Advantages Disadvantages

(a) Detergents can be an effective cleansing agent in both

hard and pure water.

(b) Detergents are more effective than soaps in hard

water because the calcium or magnesium salts from

detergents are soluble in water. Therefore detergents do

(a) Detergents with branch-chained hydrocarbons are

non-biodegradable.

(b) Formation of large amount of bubbles or foam will

restrict the oxygen supply from diffusing into the water,

hence threatens aquatic lives.

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not form scum in hard water.

(c) Detergents are also effective in acidic water because

the hydrogen ions do not combine with the anions of the

detergent.

14.4 Food Additives

1. There are two types of food additives: natural source and chemically made.

2. Food consists of organic substances. Therefore the freshness of food cannot be maintained for a long time because organic

substances tend to decay.

3. The decay of organic substances is due to the chemical reactions caused by microorganisms such as bacteria.

4. The decay of food can be prevented through preservation.

5. The function of preservatives is to destroy or prevent the growth of microorganisms in food.

6. Salt, sugar, and vinegar are examples of natural food additives.

7. Salt is widely used to preserve foods such as vegetables, meat, and fish. This is because salt will absorb the water contained in

the food and thus drying them. Without water, microorganisms cannot survive.

8. Microorganisms cannot survive in sugar solution and acidic conditions of vinegar.

9. Some permitted food preservatives are shown below:

Sulphur dioxide Propanoic acid

Benzoic acid Sodium nitrate

Sodium benzoate Sodium nitrite

Ascorbic acid Ethanoic acid

10. These preservatives are commonly used in soft drinks, syrups, fruit juices, margarine, processed meat, fish paste, and dried

vegetables.

11. Oils and fats as well as certain vitamins can undergo oxidation when exposed to air. Oxidation can decompose food into

smaller molecules which are toxic.

12. Ascorbic acid, ascorbyl palmitate, citric acid and isopropyl citrate are added to foods as antioxidants to prevent spoilage.

13. Sometimes an artificial flavouring is added to food to enhance the flavour of the food. One example is monosodium

glutamate(MSG).

14. Saccharin and aspartame are artificial sweeteners which can increase the sweetness of foods.

15. Summary of harmful side effects caused by some food additives:

Additive Likely side effect

Sugar Obesity and diabetes

Salt High blood pressure

Sodium nitrite Forms carcinogenic compounds in the body

Sulphur dioxide and

sodium benzoate

May develop sore throats and skin rashes and

hives

Aspartame Causes respiratory allergies, headaches,

dizziness, nausea and numbness

MSG Headache, burning sensation along the back of

the neck and chest pain

14.5 Understanding Medicine

1. Traditional medicines are medicines which are obtained from natural sources without being processed chemically.

2. Summary of some traditional medicines and their properties:

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Plants/Herbs Properties

Ginseng Refresh body and enhance body strength

Aloe vera Treatment of itchiness and wounds

Mint Increase body temperature and induce sweating

Cocaine Act as anesthetics

Garlic As an antibiotic, reduces the stickiness of

platelets

Ginger Treatment of flatulence in the body, warming of

the body to prevent cold

Quinine Treatment of malaria and muscle cramps

3. Modern medicines are produced chemically and often involve drugs.

4. Modern medicines usually come in the form of pills, capsules, emulsion, paste, and solution.

5. Basically modern medicines are divided into four groups according to their functions.

Analgesics

Antibiotics

Hormones and steroids

Psychotherapeutic drugs

6. Analgesics:

Analgesics are medicines that can relieve pain. Examples are aspirin, paracetamol, and codeine.

These medicines are generally used to lower the body temperature of a person suffering from high fever.

7. Antibiotics:

Antibiotics are used to treat infections caused by bacteria. Examples are penicillin and streptomycin.

8. Psychotherapeutic Drugs:

Psychotherapeutic drugs are used to treat psychiatric patients by altering their emotions as well as behaviour. These drugs can be

categorised into stimulants and antidepressants.

Examples of stimulants include amphetamine and caffeine. Antidepressants are used to control depression and to calm down a

patient. Examples include barbiturate and tranquiliser.

9. Hormones and Steroids:

Hormones are chemicals produced by human`s endocrine gland to control physiological processes and homeostasis in the human

body. Insulin is a type of hormone secreted by pancreas to control the blood sugar level. Anabolic steroids are medicines used to

treat AIDS and cancer.

Assessment 14

Objective Questions

1. Which of the following is not true about soap?

A. Soap is a mixture of sodium and sulphonic acid with 12 to 18 carbon atoms.

B. Soap is made from animal fats or vegetable oils.

C. The process of making soap is called saponification. D. Glycerol is one of the products of saponification.

2. The soap molecule has the following properties except

A. its hydrophobic end is covalently bonded B. its effectiveness decreases in heated water

C. its hydrophobic end dissolves in grease D. it reduces the surface tension of water.

3. Which of the following are correct about soap and detergent?

I Soap is ineffective in hard water as it forms scum

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II Dehydrated zinc carbonate overcomes the problem of hard and

acidic water

III Soap is more soluble in water as compared to detergent.

IV Detergent is less biodegradable compared to soap

A. I and II only B. I, II, and III only C. I and IV only D. IV only

4. The following are the advantages of using food additives except

A. delays food decay B. increases mineral and vitamin content

C. reduces health risks in the case of sorbitol D. prevents heart related diseases.

5. Food packaging labels should contain

I mass of product

II expiry date

III address of manufacturer

IV added vitamins and minerals

A. I, II, and III only B. I, II, and IV only C. II, III, and IV only D. I, II, III, and IV only

6. Analgesic is

A. a type of medicine which is used as an antidepressant

B. used to retard growth of microorganisms C. used to relieve pain

D. a type of steroid used to cure arthritis rheumatoid

7. Caffeine, nicotine, and dextroamphetamine are types of

A. antipsychotic drugs B. antidepresants C. steroids D. stimulants

8. Which of the following is most commonly used in the treatment of rheumatoid arthritis?

A. Panadol B. Prednisone C. Codeine D. Steptomycin

9. Which of the following is true about hormones?

I Hormone carries the function of controlling metabolism, physiological and

homeostatic activities in the body.

II Endocrine glands release hormones directly into the blood stream

III Excessive use of hormones may cause side effects such as insulin shock

and liver disorders.

IV Females will have the characteristics of a male when testosterone is taken e\ excessively.

A. I, II, and IV only B. I, III, and IV only C. II, III, and IV only D. I, II, III, and IV

10. Vineger, lime, onions, salt and cinnamon are all used as

A. natural flavouring B. natural stabilisers C. natural preservatives D. natural antioxidants

Structured Questions

1. Soap is manufactured by mixing fatty acids with an alkaline solution.

(a) Name the process of manufacturing soap. [1 mark]

(b) The process stated in (a) is a combination of two processes. Name the two processes.

[2 marks]

(c) One type of fatty acid that can be used to produce soap is palmitic acid. Where can it be obtained from?

[1 mark]

(d) One of the by products of manufacturing soap is an alcohol. Name that alcohol. [1 mark]

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(e) H H H H H H H H H H H H O ½ ½ ½ ½ ½ ½ ½ ½ ½ ½ ½ ½ || H—C—C—C—C—C—C—C—C—C—C—C—C—O—S—O– Na + ½ ½ ½ ½ ½ ½ ½ ½ ½ ½ ½ ½ || H H H H H H H H H H H H O

Circle the hydrophobic part of the detergent molecule above. [1 mark]

(f) Sodium carboxymethyl cellulose is added into detergents as an additive. What is its function?

[2 marks]

(g) State two disadvantages of using detergents. [2 marks]

2. (a) Turmeric powder is commonly used in cooking as a traditional food additive. Name two uses of turmeric.

[2 marks]

(b) What is tartrazine used for? [1 mark]

(c) State the method that can be used to separate tartrazine from food? [1 mark]

(d) State two uses of aspirin. [2 marks]

(e) Barbiturate is an antidepressant used as sleeping pills and to treat fits. State one of its disadvantages.

[1 mark]

(f) State three important ways of taking medication. [3 marks]

Essay Question

1. (a) Outline an experiment to prepare a sample of soap by using coconut oil in the laboratory. [8 marks]

(b) Describe the cleansing action of soap on a piece of handkerchief stained with grease. [8 marks]

(c) Give two examples of traditional medicines derived from plants and state their functions. [4 marks]

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