How can ice boil water

Save my name, email, and website in this browser for the next time I comment. This site uses Akismet to reduce spam. Learn how your comment data is processed. Skip to content Search for:. Latest news. Making Horsehair Pottery. Hagfish Slime. Paint Spinning. Turbulent Puffs. Like this: Like Loading As the video explains , you need a pressure chamber, which uses a vacuum pump to suck out all the air in the area you're working with.

Inside this, Cody sits a beaker containing 60 ml of room temperature tap water. A salt made from magnesium sulphate anhydrous and a bottle coated in calcium sulphate are also placed up the back of the chamber. These two substances aren't there to help the boiling-freezing process - they're to help absorb the water vapour so the pressure chamber isn't damaged by the build-up. A few pieces of solid calcite are then added to the water as 'boiling chips', which won't affect anything temperature-wise, but will help the water boil more smoothly.

Inside the pressure chamber, the water isn't going to be boiled by increasing the temperature - instead, it's going to be boiled by decreasing the pressure.

As Cody explains , the boiling point of a liquid depends on both temperature and pressure, and the warmer the liquid, the higher the vapour pressure. The small bubbles trapped in the ice cause the white appearance. Boiling the water removes the air dissolved in it, producing clear ice as a result. Assuming that other impurities don't produce the same cloudy effect. If the water passed through a water softener, the Ca and Mg ions may have been replaced by twice as many sodium or potassium ions.

For the gases present in water, dissolution at room temperature is an exothermic process, so their solubility decreases when the water is heated. The solubility of gases doesn't reach zero at boiling point, nor does it necessarily decrease over the whole temperature range. The sulphates sometimes referred to as "permanent hardness" , and the sodium or potassium bi carbonates stay in solution.

I'm really winging this one because the last time I did an equilibrium calculation was 35 years ago! But I'm fairly sure of a partial answer see discussion at end. A gas's solubility in water or liquid generally almost always decreases with increasing temperature.

This phenomenon is explained in a way very like the explanation of the increase in evaporation rate of a liquid with temperature. Gases dissolve in liquids because the gas molecules find a lower energy state bound to the liquid. The higher the temperature, the greater the proportion of the gas molecules with thermal energy greater than the binding energy for the dissolution process.

So a greater proportion of the gas molecules can escape from liquid: the chemical equilibrium for the dissolution reaction shifts to favor free molecules more than bound ones with increasing temperature. The boiling of a liquid lowers the concentration of dissolved gases through the above effect. Normally the shift of equilibrium back to favor dissolved gases with decreasing temperature would mean that, on cooling, the liquid would take up as much gas as is driven off in the boiling process.

The trick with clear ice is that the liquid is frozen too quickly for the gas dissolution process to complete - it is frozen irreversibly so that it is a long way from equilibrium as it cools - with the result that there is a nett expulsion of gas from the liquid by the boiling before freezing process.

Once the liquid is frozen, the gas can no longer dissolve in it, so you have clear ice. Note that this answer is incomplete: it does not answer why the gas dissolved in the liquid forms the bubbles it does when the liquid freezes, as in the right hand image of your question.

This answer only explains the absence of the gas needed for the clouding process, so a full answer needs to explain why the dissolved gas comes out of solution to form bubbles as the ice freezes.

This answer was meant as a comment to WetSavannahanimal aka Rad Vance but it is rather long and I hit the character limit. The reason for the opaque center should be due to the manner in which the water volume is freezing. Presumably the solution is not mixed and the outside freezes first forming a crystalline ice wall through which the gas cannot escape.

As the wall thickens gas is released from the water that solidifies into the central solution that remains. This concentrates the gas in the remaining liquid in the centre.

When the gas concentration in this solution hits the saturation value for the liquid at it's current state some of it exits the solution forming the cavities, simultaneously some ice should form, returning the solution to the saturation concentration.

This is repeated until all the water is frozen. The observation that clear ice is made buy bubbling gas through it as it freezes, indicates that mixing of the solution allows the saturated gasses to escape from the surface of the total water volume as the solid forms rather then forming in the center.

Now one might ask the question why is it that there isn't just a single bubble. The first reason, from a bulk solution point of view, is that the water is freezing incrementally forming bubbles as it goes. It is really oscillating about the equilibrium state of the solution, that is the gas saturation point of the freezing solution. The exact conditions of this point will vary slightly as the liquid freezes. The pressure that the ice in the center froze at is likely larger then the pressure at which the surface ice froze at for instance, similarly there is a the temperature at which it froze might also vary.

There is probably also a concentration effect, that is as this equilibrium point shifts about the gas saturation point will shift about, this change in concentration also affects the freezing point a little. There are about four effects Temperature, Pressure, Volume and Gas Concentration at play during the freezing.

The second effect, from a finite volume point of view, is that locally about the cavity the water might experience a "rush of gas" which could locally freeze a film of water encapsulating the bubble hence the final complex arrangement of cavities and not the formation of a single bubble.