How Dangerous is Your House – 1. Kitchen

Dick and Dom explore some hands-on science which you can try for yourself at home.

Science in the kitchen - ice cream, washing up, and what happens when you put marshmallows in the microwave?

Activity 1: Making ice cream without a freezer

You will need:

two freezer bags with a good seal – one small, one large (the small one should fit inside the large one with room to spare)

  • cream
  • milk
  • caster sugar
  • flavouring or soft fruit (Dick and Dom used vanilla essence)
  • ice cubes
  • salt
  • extra polythene bags in case of leaks

Pour half a cup (120ml) of cream into the smaller bag, and add 3-4 tablespoons of sugar. Add a few drops of vanilla essence (or any other flavouring of your choice). Thin out the mixture by pouring in a bit of milk. Then, seal your small bag really well - you don't want any of the ingredients leaking out.

Next, put your full small bag inside the bigger bag. Around the small bag, fill up the rest of your big bag with ice cubes and add 5-6 tablespoons of salt. Seal that well too. You then need to give the bags a really good shake for 5-10 minutes, until the cream and sugar mixture turns to ice cream. Dick and Dom found that it was useful to have a few spare polythene bags to hand to put your bigger bag into, in case of spillage. They also got very cold hands, so you might want to wear gloves!

What's happening?

The salt in the big bag reduces the melting point of the ice. In order to melt at this lower temperature, the ice cubes need energy from somewhere, and they take that from the small bag. So all of the heat from the milk-and-sugar mixture goes to melt the ice cubes, making the mixture colder. As you shake it, it turns to ice cream. The ice and salt mixture in the bigger bag gets very cold, as low as -19C.

This is why we put salt on the roads in the winter: it lowers the freezing point, which melts snow and ice, and prevents the water from re-freezing.

Activity 2: What happens when you put marshmallows in the microwave?

Activity 2: What happens when you put marshmallows in the microwave?

Make sure you have adult supervision when using the microwave.

Place 3 or 4 marshmallows on a microwavable plate. Put them in the microwave, and turn it on for about 45-60 seconds. Watch what happens to the marshmallows – and do press stop before they start to burn!

What's happening?

Microwave ovens work using a type of radiation, which makes the molecules inside your food vibrate and move around, heating it up.

Marshmallows are a good food to see this with, because they are full of air bubbles. As the microwave heats up the marshmallows, the bubbles get bigger and bigger because the molecules inside them are moving around more. And so the marshmallows grow... and grow. When you stop the microwave, the air cools down, the bubbles burst, and the marshmallows go splat.

Be careful when taking the marshmallows out of the microwave: they will be very hot, so don't eat them straight away!

Activity 3: Washing up with pepper

You will need:

  • a bowl full of water
  • ground pepper
  • washing up liquid

Sprinkle pepper across the water so you have a layer of ground pepper floating evenly across the surface.

Now, dip a finger into the water. Does anything happen?

Try it again – but this time, put of drop of washing up liquid on your finger. Does anything happen to the pepper now?

What's happening?

When you put washing up liquid into the bowl, all the pepper springs to the side. The washing up liquid has formed a layer across the water, pushing the pepper to one side. This is because it has lowered or broken the surface tension of the water. When you use washing up liquid to clean dishes, this property allows grease that would normally sit in big sheets or layers on your plates to be turned into droplets of oil, surrounded by a layer of water, which you can then wash away to leave clean plates.