Topic
Mixing & changing
Dissolving, rusting, rising, and turning into something else — 45 tiny stories from every shelf.
Sour, and eager to give something away
What Makes Something an Acid?
An acid is a substance that hands out a tiny particle, which is what makes it sour and able to eat into things.
Let’s go →Wrong-sized atoms get in the way
Why Is Pure Gold Too Soft for a Ring?
Mixing metals makes them stronger, because odd-sized atoms jam the neat rows that let metal bend.
Let’s go →Pieces too small to see
What Is Everything Made Of?
Everything is built from atoms, and there are only about a hundred different kinds to build with.
Let’s go →Where roast smells come from
Why Does Food Turn Brown When It Cooks?
Above about 140 °C, sugars and proteins react to make brown colour and roasted flavour.
Let’s go →Shaking a mixture until it gives up
How Does Cream Turn Into Butter?
Churning cream smashes the coats off fat droplets so they clump into butter.
Let’s go →Splitting a liquid into two
How Does Milk Become Cheese?
Cheese is milk split into curds and whey, with the curds pressed, salted and left to age.
Let’s go →It sets by reacting, not by drying
Why Does Concrete Go Hard Under Water?
Concrete hardens by reacting with water rather than losing it, which is why it can set at the bottom of a river.
Let’s go →A narrow window of heat
Why Does Custard Suddenly Scramble?
Egg proteins unfold and thicken custard, but a little more heat makes them clump.
Let’s go →Making a colour hold on
How Does Colour Stay in Cloth?
A dye colours cloth by bonding to the fibres themselves, rather than sitting on the surface like paint.
Let’s go →Flow into every crevice, then stop flowing
How Does Glue Hold Two Things Together?
Glue must first be runny enough to fill every tiny pit in both surfaces, and then stop being runny.
Let’s go →A mesh built from fruit
Why Does Jam Set?
Jam sets when pectin from fruit forms a mesh that traps the sugary liquid.
Let’s go →Melted, then cooled too fast to crystallise
How Do You Turn Sand Into a Window?
Glass is melted sand, cooled so fast that the atoms freeze in place before they can form crystals.
Let’s go →Mostly a surface job
What Does a Marinade Actually Do?
Marinades flavour and tenderise the surface of food — they hardly penetrate at all.
Let’s go →Mixed together, not joined together
Why Can You Get the Salt Back Out?
A mixture is stuff jumbled together but not joined, which is why you can always get the pieces back out.
Let’s go →Two things make a third thing
What Happens When Atoms Join Up?
Atoms join into molecules, and the new thing behaves nothing like the pieces it was made from.
Let’s go →A thread made from nothing that grew
Why Was Nylon Invented?
Nylon is a made fibre: long molecule chains pulled straight, giving thread that is strong, endless and rot-proof.
Let’s go →Three jobs in one tin
What Is Paint Made Of?
Paint is coloured powder held in a glue and thinned with a liquid that leaves once it is on the wall.
Let’s go →Making the jar uninhabitable
Why Does Pickling Stop Food Rotting?
Pickling makes food too acidic and too salty for the microbes that would spoil it.
Let’s go →Millions of small links, joined into chains
What Is Plastic Actually Made Of?
Plastic is made of gigantic molecules — one small unit joined to itself thousands of times into a chain.
Let’s go →Melting versus mashing
Why Does Glass Recycle Better Than Paper?
Glass and metal melt back to what they were. Paper fibres get shorter each time, so paper runs out of lives.
Let’s go →Fat, turned inside out
How Is Soap Made?
Soap is made by reacting fat or oil with a strong alkali, producing molecules with a water end and a grease end.
Let’s go →Turning tough into silky
Why Do Cooks Boil Bones for Hours?
Hours of gentle heat turn tough collagen into gelatine, giving stock its body.
Let’s go →Scrubbing, and rebuilding
What Is Toothpaste Actually Doing?
Toothpaste is a mild abrasive with detergent, flavour and fluoride — and the fluoride is the part that rebuilds enamel.
Let’s go →Nothing alive has the tool for it
Why Does Plastic Never Rot?
Plastic lasts because nothing alive has the chemical tool to cut it up, so it only ever breaks into smaller pieces.
Let’s go →Bacteria doing the thickening
How Does Milk Become Yoghurt?
Bacteria turn milk sugar into acid, which makes milk proteins clump into a soft set.
Let’s go →Throw it all out, take back what you need
What Do Kidneys Actually Do?
Kidneys clean blood by throwing nearly everything out and carefully taking back the water and salt you need.
Let’s go →The chemistry room
What Is a Liver For?
The liver is where everything you absorb goes first — to be stored, rebuilt into something useful, or made safe.
Let’s go →It depends on who does the delivering
Is Venom the Same as Poison?
Venom is injected by the animal, poison is only dangerous if you eat or touch the animal — and both are made of the same kinds of chemicals.
Let’s go →Fruit rusting
Why Does a Cut Apple Turn Brown?
A cut apple browns because a released enzyme reacts with oxygen to build brown pigment.
Let’s go →A gas being made
Why Does Baking Soda Fizz?
Baking soda fizzes because it reacts with acid to make carbon dioxide gas.
Let’s go →A fungus breathing out
Why Does Bread Rise?
Bread rises because living yeast produces gas bubbles trapped inside the dough.
Let’s go →Atoms joining a queue
How Do Crystals Grow?
Crystals grow as atoms leave a solution and lock into a repeating pattern.
Let’s go →Broken up, not vanished
Where Does Sugar Go in Water?
Dissolving breaks a solid into single molecules spread evenly through the liquid.
Let’s go →Smell molecules escaping
Why Does a Fridge Smell of Everything at Once?
Foods release smell molecules that build up in a sealed fridge and settle on everything.
Let’s go →Lowering the freezing point
Why Does Salt Melt Ice?
Salt lowers water's freezing point, so ice melts at temperatures below zero.
Let’s go →Every mix absorbs more
Why Does Mixing Paint Make Brown?
Mixed paints absorb more and more light, so the result heads towards brown.
Let’s go →A liquid that panics
Why Can You Run on Cornflour and Water?
Cornflour mixed with water jams solid when hit and flows when pressed slowly.
Let’s go →Cloudy water is useful water
Why Do Cooks Save the Pasta Water?
Pasta water carries starch, which thickens a sauce and helps it stick to the pasta.
Let’s go →Iron combining with oxygen
Why Does Metal Go Rusty?
Rust forms when iron reacts with oxygen and water to make a flaky new substance.
Let’s go →A molecule with two ends
How Does Soap Clean?
Soap works because each molecule grips grease at one end and water at the other.
Let’s go →Gas hiding in plain sight
Where Do the Bubbles in Fizzy Drinks Come From?
Fizzy drinks hold dissolved gas under pressure, and opening the bottle lets it bubble out.
Let’s go →How tightly the molecules hold
Why Are Some Things Solid and Others Runny?
Solids, liquids and gases differ in how tightly their molecules hold together.
Let’s go →Sugars and proteins reacting
Why Does Toast Go Brown?
Toast browns because heat makes sugars and proteins react into new flavour compounds.
Let’s go →Proteins forced to unfold
How Does Egg White Turn Into Foam?
Whisking unfolds egg white proteins so they wrap around air bubbles and hold them.
Let’s go →A sealed tank of chemicals
Why Does a Battery Run Out?
A battery goes flat because it holds a fixed amount of reacting chemicals, and each electron spends some.
Let’s go →