Cold Boil
 |
Poster frame from video: In most browsers, Click on image to play OR Right-click on image and "save target as" to your computer, then play in QuickTime, Windows Media Player, or another player. |
 |
 |
Water at about 40 °C boiling in a syringe |
Taranaki: Water boils at a lower temperature at higher altitudes. |
| Abstract | Water boils at room temperature
|
||
| Portable | Yes | ||
| Principles Illustrated |
Water boils at 100 °C at one atmosphere of pressure but at lower temperatures under lower pressures. Water will actually boil at room temperature if the pressure is low enough. Here we make water boil at room temperature, or more vigorously at about 40 °C, by pulling back the handle of a syringe filled with water. We can understand this as follows. the water molecules have varying amounts of energy, and some are able to leave the liquid and enter the vapour. When we reduce the pressure above the liquid by pulling down the handle of the syringe, we make it easier for water molecules to leave the liquid, thus reducing the boiling temperature. |
||
| NCEA & Science Curriculum | |||
| Teacher Guide |
Would you like to contribute lesson suggestions? Contact us. |
||
| Video | |||
| Instructions | Fill the syringe to around one quarter to one third full from a bucket of room temperature or warm water and seal the top (we usually use Blu-Tack). First pull the syringe back and wait for dissolved air to come out of the water and then return the piston to its original position gradually. You can unseal the top if you wish and expel the small air bubble that forms, but this is not essential. Now the syringe is ready for student use. Have a student pull down the plunger of the syringe to cause boiling. Mounting the syringe in a stand can make it easier for younger students to pull the plunger and also for other students to see the boiling, particularly if larger syringes are used, but have students wear goggles (see safety notes). There is a neat bit of more advanced physics here as well. If you simply partly fill the syringe with water from a bucket, expel as much of the air as possible, and pull down the syringe plunger as described above you will see boiling that is nucleated on the inside surfaces of the syringe. This is seen in our video. It looks a lot like water boiling in a glass kettle with large bubbles. Use about 20 ml of water in a 50-60 ml syringe or about 5 ml in a 20 ml syringe. But you can also see a rather different effect. If you seal a SMALL (20 ml perhaps) syringe with about 5 ml of water, pull the plunger down far and release suddenly, expel the air, and then reseal and pull it slowly you can see boiling throughout the liquid with lots of small bubbles. This effect is discussed well on the Exploratorium website: www.exploratorium.edu/mars/teachers/onmars.html. A large syringe is more likely to shatter when released suddenly. We are in the process of making a video that shows these two experiments side-by-side. |
||
| Safety | Have the students wear goggles, particularly with larger syringes. We discovered by accident that the top of the syringe can shatter if the handle is released suddenly! This is less likely to happen with the 20 ml syringes. |
||
| Related Resources | |||
| Credits |
This teaching resource was developed by the Te Reo Māori Physics Project with support from |
||
|
|||
| Copyright |