Organic products we use every day
Most things made from oil, gas and plants are organic compounds. Three families matter most:
- Polymers: very long molecules made by joining many small monomers. Examples: polythene (carrier bags), PVC (pipes, made from chloroethene) and Teflon (non-stick pans, made from tetrafluoroethene).
- Condensation products: polymers where a small molecule, usually water, leaves at each join. Nylon (clothes, ropes) and polyester (PET bottles) are made this way.
- Halogen derivatives: carbon compounds with Cl, F, Br or I. Uses: solvents like dichloromethane, refrigerants, non-stick coatings and some pesticides.
Good news: they are cheap, light and strong. Bad news: many do not rot, and some harm the environment. We must use, reuse and recycle them wisely.
Freons and ozone depletion
Freons are chlorofluorocarbons (CFCs) such as CCl2F2. They do not burn, are not poisonous to touch and are easy to turn into liquid, so they were used in fridges, air-conditioners, spray cans and foam.
But they are very stable low down, so they slowly rise to the stratosphere, 15 to 50 km up, where the ozone layer (O3) absorbs harmful ultraviolet (UV) light from the Sun. There, UV breaks a C–Cl bond:
CCl2F2 → CClF2• + Cl•
The free chlorine atom attacks ozone in a chain reaction:
Cl• + O3 → ClO• + O2
ClO• + O → Cl• + O2
Chlorine is back and starts again. It acts as a catalyst, so one Cl atom can destroy about 100,000 ozone molecules. Less ozone means more UV on Earth, which causes sunburn, skin cancer, eye damage and harm to plants and plankton.
In 1987 the world agreed on the Montreal Protocol to stop making CFCs. Safer gases replaced them, and the ozone layer is slowly recovering.
Hydrolysis and oxidation in the human body
Hydrolysis means splitting a molecule using water (hydro = water, lysis = splitting). Digestion is hydrolysis, helped by enzymes:
- Starch + water → glucose (enzyme amylase in saliva)
- Fat + water → glycerol + fatty acids (lipase)
- Protein + water → amino acids (protease)
The small pieces dissolve in blood and reach every cell.
Oxidation in the cells releases energy. The main fuel is glucose:
C6H12O6 + 6O2 → 6CO2 + 6H2O + energy
About 2,800 kJ of energy comes from each mole (180 g) of glucose. The body does it slowly in many small steps, so the energy is used and not lost as one big flame.
Proteins: primary, secondary and tertiary structure
A protein is a long chain of amino acids joined by peptide bonds (a condensation product, with water lost at each bond). There are 20 common amino acids.
- Primary structure: the order of amino acids along the chain, like the order of letters in a word.
- Secondary structure: local twisting into an α-helix (coil) or β-sheet (folded ribbon), held by hydrogen bonds between neighbouring parts.
- Tertiary structure: the whole chain folds into one 3D shape, held by bonds between side chains (hydrogen bonds, ionic bonds, sulphur bridges, oily parts hiding inside).
Several chains together give a quaternary structure (haemoglobin has four). Heat, acid or alcohol break the weak bonds, so the protein unfolds. This is denaturation: when you boil an egg, the white goes solid and cannot go back.
Enzymes and hormones
Enzymes are proteins that act as biological catalysts. The substrate fits into a pocket called the active site, like a key in a lock, so each enzyme works on one kind of substrate. They speed reactions up millions of times and are not used up. They work best at a particular temperature (about 37 °C in the human body) and pH. Too hot, and the shape is lost.
Hormones are chemical messengers made by glands and carried by the blood to target cells. They control growth, mood, sugar level and more. Insulin (a small protein of 51 amino acids) lowers blood glucose; adrenaline (a small amine) prepares the body for action; thyroxine controls the speed of body chemistry. Too much or too little of a hormone causes illness, such as diabetes when insulin is lacking.
Use wisely: safety and environment
Organic products help us, but we must manage them: recycle plastics, never burn PVC in the open (it gives toxic gas), return old fridges so CFC gas is collected, and keep pesticides away from water. Choosing the right compound for the job is chemistry; using it with care is responsibility.
Key formulas and definitions
- CCl2F2 → CClF2• + Cl• (UV, in the stratosphere)
- Cl• + O3 → ClO• + O2 and ClO• + O → Cl• + O2 (catalytic cycle)
- C6H12O6 + 6O2 → 6CO2 + 6H2O + energy (about 2,800 kJ per mole)
- Starch / fat / protein + water → glucose / glycerol + fatty acids / amino acids (hydrolysis)
- Protein levels: primary (sequence) → secondary (helix, sheet) → tertiary (3D fold)
Worked examples
1. Which part of a CFC molecule harms ozone, and what makes it free?
The chlorine atom. UV light in the stratosphere breaks the C–Cl bond and releases a free Cl atom, which then attacks ozone.
2. One chlorine atom destroys about 100,000 ozone molecules. How many are lost by 3 x 10^6 free Cl atoms?
3 x 10^6 x 10^5 = 3 x 10^11 ozone molecules.
3. How many moles and how many grams of CO2 form when 0.5 mol of glucose is fully oxidised? How much energy is released (2,800 kJ per mole)?
1 mol glucose gives 6 mol CO2, so 0.5 mol gives 3 mol CO2. Mass = 3 x 44 = 132 g. Energy = 0.5 x 2,800 = 1,400 kJ.
4. Write what happens when starch is digested and name the type of reaction.
Starch + water → glucose. This is hydrolysis, helped by the enzyme amylase.
5. Explain why boiling an egg cannot be reversed.
Heat breaks the weak bonds that hold the folded shape of the egg-white proteins, so they unfold and stick together. This is denaturation, and the original shape does not return.
6. Why does an enzyme work for one substrate only?
Its active site has a special 3D shape that fits only one substrate, like a key in one lock.
Common mistakes
- Saying CFCs are used up when they destroy ozone. The chlorine atom comes out unchanged each time, which is why one atom does so much harm.
- Confusing hydrolysis (adding water to split) with condensation (joining and losing water). They are opposites.
- Thinking the ozone layer is at ground level. Good ozone is high in the stratosphere; ozone near the ground is a pollutant.
- Mixing up the protein levels: primary is the sequence, secondary is the coil or sheet, tertiary is the whole fold.