# Finding Absolute Zero

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#### Updated on Sep 04, 2013

Have you ever put a marshmallow in the microwave? If you haven’t, here is video to watch.

As the gases inside the marshmallow are heated by the microwave, their molecules move around more and more. The molecules start bumping into each other, and they push each other apart. When gases gain more energy, they need more space, causing the marshmallow to puff out. A French scientist named Jacques Charles described how gases change with temperature back in 1780s.He stated that if the mass and pressure are kept the same in a gas, then the volume of the gas changes directly with temperature. This property of gases is called Charles’ Law: V1/T1=V2/T2

If gases expand as they are heated, it stands to reason that they would contract as they cool. Here is a video of an inflated balloon being placed in liquid nitrogen.

What if you cool the gas so much that none of the particles moved around anymore? That would also mean the molecules could be infinitely close together, making the volume of the gas 0. This can’t actually happen, but scientists like to think theoretically. This temperature at which all molecular motion stops is called absolute zero.

Even though you can’t lower the temperature of a gas to absolute zero, you can do an experiment that gives you a quantitative value for the relationship between gas and volume. Once you have figured out two volume-to-temperature points, you can plot a line, and once you have line, you can extrapolate (extend using known information) your line to see what temperature absolute zero would be.

### Problem

How can the value of absolute zero be determined?

### Materials

All the glass materials must be made of some sort of Pyrex-like material, to prevent shattering during temperature changes.

• Bucket
• Ice
• Big spoon
• Water
• Safety goggles
• Large beaker, at least 500 mL
• One-hole rubber stopper that fits the 125 mL flask
• Short glass rod (5- 10 cm) that fits snuggly into the stopper hole
• Ring stand
• Clamp
• Hot plate
• Tongs big enough to hold the 125 mL flask
• Celsius thermometer
• Graph paper
• Ruler

### Procedure

1. Make an ice bath by filling the bucket with ice and adding cool water. The bucket should be 3/4 full.
2. Using the big spoon, stir the ice bath occasionally.
3. Put the one hole stopper into the dry 125 mL flask.
4. Set up a hot water bath. The 500 mL beaker should be on the hot plate.
5. Clamp the 125 mL flask upright so that most of flask is submerged in the hot water bath. (See diagram 1)
6. Boil the water with the empty flask inside it for five minutes. You are doing this so that the gas inside the flask reaches the same temperature as that of the boiling water.
7. Record the temperature of the boiling water (which should be the same as that of the gas inside the flask). Try to get a measurement to 0.1 degrees C. The more precise your measurements are, the more precise your determination of absolute zero will be.
8. While the beaker is still in the hot water bath, carefully place the short glass rod into the hole in the flask’s stopper.
9. Using the tongs, remove the flask from the hot bath.
10. Invert the Erlenmeyer flask and place into the ice bath. (See diagram 2)
11. Making sure the flask is underwater, remove the glass rod in the stopper.
12. Keep the flask submerged in the ice bath for 6-7 minutes, stirring the ice bath occasionally. Water should creep inside the flask. Why?
13. Using your fingers, which might get chilly, raise the inverted flask until the water level inside and outside the flask are the same. This is to ensure that the pressure inside the flask is equal to atmospheric pressure. The only variable you want in this experiment is temperature.
14. Measure the temperature of the water in the ice bath.
15. 16. Reinsert the glass rod into the stopper. Take the flask out of the water and set it upright.
16. Using the graduated cylinder, record the volume of water in the flask as precisely as possible.
17. Fill the flask to the level where the stopper was.
18. Using the graduated cylinder, record the total volume of the flask.
19. Subtract the volume of the water that moved into the flask from the total volume of the flask. This is the volume of the gas inside the flask after cooling.
20. Your data table should look something like this:
 Data Points Temperature in Celsius Volume in mL 1 (record temperature of the flask in the boiling water) (total volume of flask) 2 (record temperature of the ice bath) (total volume of flask minus volume of water that moved in)
1. On your graph, temperature should be on the x-axis. The range of temperatures should be from -300 to about 150 degrees C. Volume in mL should be on your y-axis. The range of volumes should be from 150 mL to 0 mL.