Chemistry in Everyday Life: One Mark Questions, Book Back Answers and Notes

About Chemistry in Everyday Life

Medium ~120 min study

The tablet you take for a headache, the preservative in a pickle bottle, the soap in your bathroom and the plastic bucket beside it are all products of chemistry. This unit looks at how these substances are made and why they work, using the organic chemistry you learnt in the earlier units.

The unit moves from the very small to the large. It begins with a drug molecule binding to an enzyme or a receptor protein, and ends with polymer chains thousands of units long. The common thread is that structure decides behaviour. A drug works only if its shape fits the active site or receptor it targets, and a detergent with a branched hydrocarbon tail is broken down by bacteria far more slowly than one with a straight chain.

Questions from this unit are mostly about classification and examples. You may be asked to name an antacid or a tranquiliser, explain why soap does not lather in hard water, identify the monomers of Nylon-6,6, Terylene or Buna-S, or give an example of a biodegradable polymer. Make a table of each class with two textbook examples.

What you'll learn

• Classify drugs by their therapeutic effect and give examples of each class.
• Explain how drugs interact with enzymes and receptors.
• Name common food additives and state what each one does.
• Distinguish soaps from synthetic detergents by structure and behaviour in hard water.
• Write the monomers and reactions for common addition and condensation polymers.
• Explain why biodegradable polymers such as PHBV reduce environmental waste.

Before you start

• Organic functional groups and the structures of simple molecules.
• Intermolecular forces such as hydrogen bonding and van der Waals forces.
• Basic idea of enzymes and receptors in living cells.

Chemistry in Everyday Life explained

Medicines, Food Additives, Cleansing Agents and Polymers

How Drugs Act

Drugs are chemicals that interact with macromolecules in the body to produce a biological response; those used to treat disease are medicines. Most drug targets are proteins, mainly enzymes and receptors. An enzyme inhibitor can block the active site so the substrate cannot bind, which is competitive inhibition. Or it can bind at another place on the enzyme, called an allosteric site, which changes the shape of the active site so the substrate no longer fits. Receptors are proteins in cell membranes that receive chemical messengers. A drug that blocks a receptor and stops the natural message is an antagonist. A drug that imitates the natural messenger and switches the receptor on is an agonist, which is useful when the body lacks that messenger. Choosing the right target helps keep side effects low.

Classification of Drugs

Drugs can be classified in four ways: by pharmacological effect, by action on a particular biochemical process, by chemical structure and by molecular target. Grouping by effect brings together all analgesics, which relieve pain, or all antiseptics, which kill or stop the growth of microorganisms on living tissue. Grouping by structure is useful because similar structures often act alike, as in the sulpha drugs. The unit covers antacids, which neutralise excess stomach acid, antihistamines, which block the action of histamine in allergic reactions, and tranquilisers, which reduce anxiety and stress. Some tranquilisers act as sleep-inducing hypnotics at higher doses.

Food Additives

Chemicals are added to food to keep it longer, improve its look and taste, or add nutrition. Preservatives stop microorganisms from growing; common ones are table salt, sugar, vegetable oil and sodium benzoate. Artificial sweeteners such as saccharin, aspartame and sucralose are many times sweeter than sucrose, so only tiny amounts are needed and they add almost no calories, which suits people with diabetes. Aspartame breaks down on heating, so it is used only in cold foods and drinks. Antioxidants such as BHT and BHA slow the oxidation of fats and oils, so food does not turn rancid.

Soaps and Synthetic Detergents

Soaps are sodium or potassium salts of long-chain fatty acids such as stearic, palmitic and oleic acids. They are made by saponification, heating an oil or fat with sodium hydroxide. In hard water, Ca²⁺ and Mg²⁺ ions form an insoluble scum with soap, so soap is wasted and does not lather. Synthetic detergents, such as sodium alkylbenzene sulphonates and sodium alkyl sulphates, do not form insoluble salts with these ions and work in hard water too. Both soaps and detergents have a long hydrophobic tail and a hydrophilic head. In water they form micelles, with the tails dissolved in the oil droplet and the heads facing out into the water, so the grease is lifted off and washed away.

Polymers

Polymers are large molecules built from many small repeating units called monomers. In addition polymerisation, unsaturated monomers such as ethene, styrene or chloroethene join in a chain reaction, often started by free radicals, and nothing is lost. Polythene, PVC and the synthetic rubber Buna-S (from buta-1,3-diene and styrene) are made this way. In condensation polymerisation, monomers with two functional groups join and a small molecule such as water or methanol is removed each time. Terylene is made from ethylene glycol and terephthalic acid; Nylon-6,6 is made from hexamethylenediamine and adipic acid. These are strong fibres used for clothing and ropes.

Biodegradable Polymers

Most synthetic polymers are not broken down by microorganisms, so they build up as waste in the environment. Biodegradable polymers contain functional groups, such as ester and amide links, similar to those in natural polymers, and bacteria can break them down. PHBV is a copolymer of 3-hydroxybutanoic acid and 3-hydroxypentanoic acid, used in packaging and orthopaedic devices. Nylon-2-nylon-6 is a polyamide made from glycine and aminocaproic acid. Because microbes can digest them, they do not pile up in soil the way polythene does.

Common mistakes to avoid

• Confusing analgesics with tranquilisers. Analgesics such as aspirin relieve pain; tranquilisers such as equanil reduce anxiety and mental tension.
• Assuming all detergents are biodegradable. Detergents with branched hydrocarbon chains are broken down slowly and pollute water; straight-chain ones break down more easily.
• Writing the wrong monomer pair for a condensation polymer. Terylene needs a diol and a dicarboxylic acid, but Nylon-6,6 needs a diamine (hexamethylenediamine) and a dicarboxylic acid (adipic acid).
• Treating antiseptics and disinfectants as the same thing. Antiseptics are safe on living tissue; disinfectants are used on floors and drains. The same compound can be both: 0.2% phenol is an antiseptic, while 1% phenol is a disinfectant.

Test yourself on these with the practice test, then check the worked reasoning in the solved MCQs.

Frequently asked questions

What is the difference between an agonist and an antagonist?

Both bind to a receptor. An antagonist blocks the receptor so the natural chemical messenger cannot act, which helps when the message itself is causing harm. An agonist imitates the natural messenger and switches the receptor on, which helps when the body is not producing enough of that messenger.

How do antacids relieve acidity?

Antacids such as magnesium hydroxide and aluminium hydroxide are weak bases that neutralise excess hydrochloric acid in the stomach. They treat the symptom, not the cause. Drugs such as cimetidine and ranitidine work differently: they stop histamine from binding to receptors in the stomach wall, so less acid is produced in the first place.

Why are artificial sweeteners used instead of sugar in some diets?

Sweeteners such as saccharin and sucralose are hundreds of times sweeter than sucrose, so only a trace is needed and they add practically no calories. Saccharin passes out of the body in urine unchanged. This makes them suitable for people with diabetes and for those controlling their weight.

What makes a polymer biodegradable?

A biodegradable polymer contains groups such as ester or amide links that enzymes from microorganisms can break, much as they break natural polymers. PHBV and Nylon-2-nylon-6 are the textbook examples. They are broken down in soil and water instead of piling up as waste.

What is the difference between addition and condensation polymerisation?

In addition polymerisation, unsaturated monomers join one after another and no atoms are lost, so the polymer has the same empirical formula as the monomer; polythene from ethene is an example. In condensation polymerisation, monomers with two functional groups react and a small molecule such as water, methanol or HCl is removed at each step, as in Nylon-6,6 and Terylene.

How does a detergent differ from a soap?

Soaps are sodium or potassium salts of long-chain fatty acids, with a –COO– head. They form insoluble scum with calcium and magnesium ions, so they do not work well in hard water. Anionic detergents are sodium salts of long-chain alkyl hydrogen sulphates or alkylbenzene sulphonates, whose calcium and magnesium salts are soluble, so they work in hard water as well.