Kitchen Science Experiments for Kids: The Amounts the Instructions Leave Out

Start with the volcano, and put the baking soda in first

The volcano fizzed for two seconds and stopped, and the child turned round to ask what went wrong. It stopped because there was too little baking soda in the bottle, not because the vinegar was the wrong sort. Use more soda than looks sensible and the same bottle runs for half a minute.

You need a narrow bottle or tall glass, baking soda, kitchen vinegar, a squeeze of dishwashing liquid, food colouring and a tray. Spoon two heaped tablespoons of baking soda into the bottle, add the soap and a few drops of colour, and swirl it while it is still dry. Then pour in about half a glass of vinegar in one go.

The order matters more than the amounts do. Soda first and vinegar last, poured fast rather than trickled, is what sends foam climbing instead of bubbling politely at the bottom.

Why does the fizz die after two seconds?

Three things kill it, and the bottle tells you which one. A fizz that stops almost at once means the soda ran out first, so the fix is more soda rather than more vinegar. A fizz that never climbs means the container is too wide, and the same mixture in a drinking glass will rise where it spread out flat in a bowl.

The third is tired baking soda. A packet left open in a humid kitchen goes hard, and a lump reacts only on its outside, so press the lumps flat with the back of a spoon before they go in.

Once the fizzing finishes the reaction is finished with it, and stirring will not restart it. Tip it out, rinse the bottle and start again with fresh soda.

Make an egg float, then make it hang in the middle

This one needs nothing you would have to go out and buy. Fill a tall glass two thirds with water, then stir in table salt a tablespoon at a time, waiting for the water to run clear again between each spoon. Somewhere around four to six tablespoons, in a glass that size, the egg stops sitting on the bottom.

Lower the egg in on a spoon rather than dropping it, both because it cracks and because a dropped egg stirs up salt that never dissolved. Undissolved salt is the failure almost everyone hits, and it reads as floating until somebody tilts the glass.

Once it floats, pour plain water very slowly down the back of a spoon held against the inside of the glass. The fresh water sits on the salt water without mixing and the egg hangs between the layers. Ask what they think stirring will do, then let them stir it.

What makes the colours run in a plate of milk?

Fat does, which is why this one fails with whatever milk happens to be open. Pour full-cream milk into a shallow plate, deep enough to cover the bottom and no more, and leave it until the surface is still. Put four separate drops of food colouring near the middle, spaced apart, and do not stir them.

Dip a cotton bud in dishwashing liquid, hold the tip in the milk between the drops, and keep it still while you count to ten. The colour runs away from it in ribbons, and stirring spoils the one movement worth watching.

The soap pulls on the fat in the milk and drags the colour along with it. Low-fat milk gives a weak version and water none at all, so when nothing moves, check the carton first.

Before you pour the vinegar

Read the label on the bottle first. Vinegar is sold here at more than one strength, and the stronger kitchen bottles print their acid share on the front. If yours does, dilute one part vinegar with four parts water before a child handles it, and keep all of it away from eyes.

Everything on the tray is food except the dishwashing liquid, which is the one to keep out of reach of a child who still puts things in their mouth. Under three, do the pouring yourself and hand over the stirring and the watching.

Do all of it on a tray, or outside if the weather allows. Food colouring stains clothes, grout and the good tablecloth.

How do you turn one experiment into three?

Change one thing, and ask for a prediction before you change it. Warm vinegar against cold, a narrow bottle against a wide bowl, sugar instead of salt in the egg glass, low-fat milk instead of full-cream. Say out loud what you each expect, run it, and say whether you were right.

That is the difference between a trick and an experiment, and it costs nothing. A child who has predicted something is watching for a reason; one who has been shown something waits for the next one.

If it becomes a standing Saturday request, the activity finder lists science and STEM classes by city and age band, and the activity quiz narrows that list by what a child already gravitates to. Neither replaces a wet tray and an argument about an egg.