How to: instantly turn water into ice

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Mark Miodownik, presenter from Dara O Briain's Science Club on BBC Two, reveals how you can perform simple science experiments at home. By carefully supercooling water you can transform it into ice instantly and create your own ice sculptures.

'Supercooling' is when you chill a liquid below its freezing point without it becoming solid. Try this amazing trick by following Mark's simple step-by-step instructions.

Mark Miodownik pours supercooled water on to ice in a bowl You can rapidly cool water below its normal freezing temperature. It will instantly turn into ice when you kick-start the crystallisation process.
pouring salt Start off by placing one bottle of water into a large bucket. Pour in 3kg of ice cubes and 1.5kg of salt. Then fill the bucket with water up to the bottle's lid. Repeat the process with a second bucket and bottle.
mark checks the bottle Do not disturb your bottles while they are cooling, as the smallest knock can start the freezing process. If you have a suitable themometer, check the temperature of the water. When it reaches between -7C and -8C carefully lift one bottle out of its bucket. Otherwise leave it for 30 to 45 minutes.
Mark puts ice cubes in a mixing bowl Place some ice cubes in a clear mixing bowl and carefully unscrew the bottle lid.
pouring water Slowly pour your supercooled water into the bowl. As it hits the ice cubes the water will crystallise, freezing almost instantly.
pouring water You can create impressive 'ice stalagmites' and even freeze the water back into the bottle.
Mark taps a bottle of bottle of cooled water onto a table Now lift out your other bottle and wipe if carefully with a towel. Give it a sharp tap on the table and watch as it rapidly turns into ice.
ice forming in bottles Tapping the bottle causes microscopic bubbles to emerge, which ice forms around.

Things you'll need:

  • Two 1 litre bottles of water (deionised water for car batteries works best, but you could use filtered water)
  • A thermometer (optional)
  • A clear mixing bowl
  • Two buckets
  • 8kg of ice cubes
  • 3kg of table salt
  • Towel

How to do it:

The experiment can sometimes fail if a bottle is knocked by accident. You can increase your chances of success by putting two bottles of deionised water in each bucket.

1.

Why doesn't the water freeze at 0C?

Ice cold water in bottle

Water tends to freeze at 0C but there needs to be a 'nucleus' around which the crystalline structure of ice can form. So filtered water can be chilled well below this as there are no impurities for ice crystals to form around, unlike normal water.

In this experiment, the ice cubes in the bowl, and the bubbles that form when you tap the bottle, act as the 'nucleus' to kick-start crystallisation.

Place a bottle of deionised water into a bucket and pack 3kg of ice around the base of the bottle. Leave a few ice cubes aside in the freezer, to use later. Pour 1.5kg of salt over the ice and top up with water until it fills the bucket to the level of the bottle's lid. Repeat the process with the second bucket and bottle.

2.

Do not disturb your bottles while they are cooling, as the smallest knock can start the ice crystallisation process. Carefully check the temperature of the water using a thermometer. You need to wait for it to cool down to -8C. This process will take around 30 minutes.

3.

Carefully take one of your bottles out of its bucket and check it is still liquid water. Place it on the table.

4.

Why does adding salt to ice water make it get colder?

When water and ice are mixed together some molecules of ice are melting and some of the water molecules are freezing.

When the temperature reaches 0C the two processes balance each other out in what is known as dynamic equilibrium.

However, salt upsets this balance. This is because salt dissolves in water but can't interact with ice.

The salt molecules start to replace the water molecules so there are fewer water molecules freezing compared to the number of ice molecules melting.

The water cools down below 0C so more molecules will freeze to achieve balance once again. The more salt you add, the colder the icy water gets.

Take the ice cubes you set aside and place into a mixing bowl. Now gently unscrew the top of your water bottle and slowly pour onto the ice cubes. Watch in amazement as the water turns instantly into ice!

5.

Now carefully lift out the other bottle of water from its ice bucket. Gently wipe it over with a towel. Then, holding it firmly by the lid, give it a sharp tap on the table. You should soon see ice begin to form at the top of the bottle and 'creep' downwards.

Send your supercooling pictures to us @BBCScienceClub. We'll post a selection of the best icy pics.

Dara O Briain's Science Club is at 8pm, Thursdays throughout August 2013 on BBC Two.

Mark Miodownik freezes and thaws a carrot to show how ice damages cells. He also reveals the process of crystallisation using sodium acetate in water.

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