Wednesday, October 9, 2013

Today's Video: In Hot Water

Is boiling water always hot? The answer is "No!"

Today I am filming a video about boiling water. 

What will you need for this experiment? A small syringe, like the one below, often used for baby medicine. You can find this at your local pharmacy.

The idea behind this demo is the Ideal Gas Law. 

In this demo, you will cap the the syringe with your thumb and then pull on it. This decreases the air pressure inside. Increasing the volume decreases the pressure according to the Ideal Gas Law: pV=nRT  

This occurs because water will boil easier at a lower pressure. 

To perform the demo:

  1.  you will first heat water to 4o degrees Celsius, when it is warm to the touch, not hot, not boiling yet. 
  2. Then you will put the water in the syringe. 
  3. Make sure that there are no air bubbles by flicking it.
  4. The water should just barely start leaking out of the top as you cap the syringe with your thumb and put your fingers on the bottom.  
  5. Pulling on the syringe causes bubbles to form.This is because the water is boiling. The decreased pressure is boiling the water.

One advantage of this exercise t is that the syringes are fairly cheap, and you can buy six or more, so students in the class can take turns boiling water and learning about volume and pressure. What a hands-on way to gain understanding of the Ideal Gas Law!

For a more detailed and visual explanation, you will just have to watch my video. Anticipation! 

The video will also include tips for how to perform this demo using oil, as well as how to perform this demo on a larger scale using a vacuum chamber and vacuum pump.

 In each of my videos, I include advice about how to perform the demo or experiment, especially for those of you trying the experiments for the first time. However, I always advise running the experiment on your own first before performing it for your class. 

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