πŸ“˜ CodingMarble Learn

Synthesised Materials: Plastics and Medicines

Synthesised (man-made) materials are made in labs and factories by chemical reactions. Plastics are long chains (polymers) built from small units (monomers). Medicines are molecules with a shape that fits a target in the body, like a key in a lock.

🎬 Step-by-step story

  1. Loose molecules float about. Chemists can join them in new ways to make things nature does not give us.
  2. These are small units called monomers. Right now every unit is alone.
  3. Watch the units join, one by one, into a long chain. A long chain of units is a polymer. This is how plastic is made.
  4. A longer chain makes a stronger plastic. Move the slider and see the strength bar change.
  5. Now medicines. A medicine molecule fits a target in the body like a key fits a lock. A molecule with the wrong shape does not fit.
  6. Free play: pick plastic or medicine and try it yourself.

Tip: drag the 3D scene to turn it. Use two fingers to zoom.

πŸ€” Common doubts, cleared

Where do the monomers come from?

Mostly from crude oil or natural gas, which are broken into small molecules like ethene in a factory. Plant-based sources are also used.

Why does a longer chain make a stronger plastic?

Long chains tangle and cling to each other, like a bowl of noodles. Short chains slide apart easily. Move the slider to see the strength bar rise.

Is plastic the same as polymer?

Plastic is one kind of polymer. Rubber, DNA and cotton are polymers too.

Why does a wrong-shaped molecule not work as medicine?

It cannot fit the target, so it cannot switch it on or off. Watch the red ball bounce away in the 3D.

Are synthetic medicines safer than natural ones?

Neither is automatically safe. A medicine is safe when tested, used in the right dose and only when needed.

What is a synthesised material?

A synthesised (or synthetic) material is one that people make by chemical reactions. Nature gives us cotton, wool, rubber and willow bark. Chemists made nylon, polyester, plastics and aspirin.

Why make them? They can be cheaper, stronger, lighter, or safer than natural things, and we can make as much as we need.

Plastics: long chains from small units

A monomer is a small molecule. Many monomers join to make a long chain called a polymer. Plastic is a polymer. Example: ethene units join to make polythene (polyethylene).

Two families. Thermoplastics (polythene, PVC, PET) soften when heated and can be melted and moulded again. Thermosetting plastics (Bakelite, used in switches and pan handles) set hard once and cannot be melted again.

Why we use plastic: light, cheap, waterproof, does not rust, easy to shape. Problem: germs cannot easily break the long chains down, so plastic waste stays for hundreds of years and breaks into tiny pieces (microplastics). Use the 4 Rs: refuse, reduce, reuse, recycle.

Medicines: molecules that fit

A medicine (drug) is a chemical that changes something in the body to cure, stop or prevent illness. Many act on a target, usually a protein. The drug molecule has a shape that fits the target like a key in a lock. If the shape is wrong, it does nothing.

Some medicines come from nature (willow bark gave the idea for aspirin). Chemists then copy and improve them in the lab: aspirin is made from salicylic acid. Antibiotics kill bacteria but do not work on viruses. Always take medicine in the dose a doctor says, and finish an antibiotic course.

Try it: spot the made-by-chemistry things

Look at the labels in your home. Find 5 things made of polyester, nylon, PET or other plastic. Find the medicine box and read the active ingredient. Sort everything into "natural" and "synthesised". Then drag the slider in the 3D to see why a longer polymer chain feels stronger.

Key formulas and definitions

Worked examples

1. A polythene chain is made from 1000 ethene units. Each ethene has 2 carbon atoms. How many carbon atoms are in the chain?

1000 Γ— 2 = 2000 carbon atoms.

2. A pan handle of Bakelite and a PET water bottle are both heated strongly. Which one can be melted and moulded again?

PET is a thermoplastic, so it softens and can be reshaped. Bakelite is thermosetting, so it stays hard and chars instead.

3. A doctor orders 10 mg of a medicine for each kg of body weight. How many mg does a 20 kg child get?

10 mg Γ— 20 = 200 mg. (Only a doctor decides a real dose.)

4. Ethene has molar mass 28 g/mol. What is the approximate molar mass of a polythene chain of 500 units?

28 Γ— 500 = 14 000 g/mol.

Common mistakes

Practice quiz

1. A small unit that joins to make a plastic is a:
2. Which of these is a synthetic fibre?
3. A plastic that sets hard once and cannot be melted again is:
4. A medicine molecule acts like a:
5. Antibiotics work against:

Practice: answer these yourself

Type or choose your answer, then press Check. Use a hint if you are stuck; the full solution appears after you answer.

Frequently asked questions

What is the difference between a monomer and a polymer?

A monomer is one small unit. A polymer is a very long chain made of many monomers joined together.

Why does plastic last so long in nature?

Its long chains are strong and germs do not have the tools to break them down, so it stays for hundreds of years.

Is every medicine made in a lab?

No. Some come straight from plants or moulds, but many are made or improved by chemists so they work better and can be made in large amounts.

Learn first

Learn next

Related lessons

All Chemistry lessons