Chemistry and health: food and medicines
Food
Food has carbohydrates, proteins, fats, vitamins, minerals and water. Energy per gram: carbohydrate and protein about 17 kJ, fat about 37 kJ. Vitamins and minerals give no energy but run body reactions (for example iron in blood, calcium in bones). A balanced diet mixes all of them.
Medicines
A medicine works only in the right dose. Too little does not cure. Too much harms. The safe, working range is the therapeutic window. Antibiotics kill bacteria (not viruses). If we stop early or take them for a cold, the strongest bacteria survive and become resistant. See also Chemistry in everyday life.
Materials: choose by property
- Metals and alloys (steel): strong, shiny, carry heat and electricity. Bridges, tools, wires.
- Polymers / plastics: light, do not rust, usually insulate. Bottles, pipes, cable covers. See Polymers.
- Glass: clear and does not react with most liquids, but brittle.
- Ceramics: hard, do not melt easily. Tiles, cooking pots, furnace linings.
- Composites (for example fibre-glass): two materials joined to get both good properties.
The rule: use matches property. Also think about cost, weight, safety and what happens when it is thrown away.
The chemical industry
A chemical industry turns raw materials (air, water, minerals, crude oil, plants) into products people need: fertilisers, plastics, medicines, soap, cement, fuels.
Example chain. Nitrogen from air + hydrogen from natural gas → ammonia (see Haber process) → urea fertiliser → more crops. The same ammonia is also used for explosives, cleaning liquids and fibres.
Factory ideas: choose a catalyst to save energy, recycle unused reactants, treat waste, and keep workers and neighbours safe. Good factories aim for high yield and low waste (Green chemistry).
Social issues: weigh benefit and harm
Every chemical product has benefits and harms. A fair decision lists both and asks who is affected.
- Plastic: cheap and hygienic, but waste lasts for years. Remedy: reduce, reuse, recycle, design for recycling.
- Fertiliser: more food, but run-off causes algae growth and kills fish. Remedy: right amount at the right time.
- Antibiotics: save lives, but misuse creates resistant germs. Remedy: only with a doctor's advice, full course.
STSE thinking: science (what happens), technology (how we use it), society (who gains or loses), environment (long-term effect). Good citizens ask for facts, not only fear or hype.
Try it: your own benefit–harm balance
Predict, then check. In the 3D free play choose Plastic and set care to 0. Predict which side is heavier, then check. Slide care up and note the value where the balance is level. At home: check a food label for energy (kJ) per 100 g, list the plastic items you used today, and mark which you could reuse. Write one rule you will follow.
Key formulas and definitions
- Energy: carbohydrate ≈ 17 kJ/g, protein ≈ 17 kJ/g, fat ≈ 37 kJ/g
- Energy in food (kJ) = grams × kJ per gram
- Safe dose lies in the therapeutic window (between too low and too high)
- Atom economy = useful mass ÷ total reactant mass × 100
- Decide: benefit vs harm, then reduce harm by care
Worked examples
1. A snack has 20 g carbohydrate, 5 g protein and 10 g fat. Find its energy.
20 × 17 = 340; 5 × 17 = 85; 10 × 37 = 370. Total = 340 + 85 + 370 = 795 kJ.
2. Why is a cooking pot not made of plastic but a handle can be?
Plastic melts at low temperature, so it cannot touch the flame. But it is a poor conductor of heat, so it is good for the handle.
3. A medicine works between 3 and 7 units. A patient takes 9. What may happen?
9 is above the window, so the drug can harm the body (side effects, poisoning). Stay in the safe range.
4. In a model, fertiliser has benefit 7 and harm = 10 − care. For what care is it balanced?
Balanced when harm = benefit: 10 − care = 7, so care = 3.
5. Ammonia plant: 28 t of N₂ and 6 t of H₂ react fully to make NH₃. What mass of NH₃ forms? (N₂ + 3 H₂ → 2 NH₃)
Mass is conserved: 28 + 6 = 34 t of NH₃ The ratio 28 : 6 : 34 also matches the equation.
Common mistakes
- Thinking "natural" means safe and "chemical" means harmful. Everything is chemicals, even water; dose and use decide the risk.
- Taking antibiotics for a cold. A cold is caused by a virus, and antibiotics do not kill viruses.
- Choosing a material only by cost, without checking whether its property fits the job.
- Judging a product by benefit only or harm only. Always list both and the people affected.