Finding Absolute Zero Experimentally: Investigating a Capillary Tube

[miniradman]

We were presented with a task of calculating the temperature of absolute zero experimentally.

To do this, we were given a capillary tube with one end sealed. Then we heated the tube up in a bunsen burner and quickly put the open end in some cooking oil. The oil was sucked up as the gas within the tube cooled down. The result of this was that there was a small section of the tube filled with oil. (image of setup attatched)

Once we had out tube filled, we exposed them to 4 different temperatures (5^oC, 25^oC, 55^oC and 90^oC and measured (using a ruler) the length of the gas in between the oil and sealed end of the tube.

Once we had these points we graphed them to get a y=mx+c function. The only problem is that my c value (when the volume equals zero) is around -150^oC. I've repeated the experiment 4 times with the same results and I don't know what is affecting the results so severly.

Any ideas would be greatly appreciated

 

[Borek]

calculating the temperature of absolute zero experimentally

Determining, not calculating. Or calculating from experimental results.

I've repeated the experiment 4 times with the same results and I don't know what is affecting the results so severly.

Same tube with same oil sample each time?

Can you show numbers you got?

I never did such an experiment, and I have no clever ideas about what went wrong. But I agree with you that the error seems way too large. While air is not an ideal gas, it can be approximated by one quite accurately.

 

[HallsofIvy]

Are you certain that the gas was at 5C, 25C, etc.? It is very difficult to hold something at a specific temperature like that. With 0C, you can put it into a bath of melting ice, or with 100C, boiling water- water will stay at those temperatures as long as there is still some ice or water left. One other temperature you can be sure of is "room temperature"- let the object sit for an extended period, then measure the temperature of the air. Water does not "stay" at other temperatures.

 

[miniradman]

Determining, not calculating. Or calculating from experimental results.

sorry :rofl:

Same tube with same oil sample each time?

Can you show numbers you got?

I never did such an experiment, and I have no clever ideas about what went wrong. But I agree with you that the error seems way too large. While air is not an ideal gas, it can be approximated by one quite accurately.

Well, I used identical capillary tubes but the amount of oil was in the same, not was it in the same place (its a little hard to get exact). But even when the oil wasn't the same for each test, the c values for the linear equation I got were very close to all tests.

err... I only have the results for the test I intended to use for my practical report. But I know for a fact that everyone in the class (all 2 of them) and the teacher had around -150 degrees celcius as well.

25^oC = 3cm
52^oC = 3.5cm
91^oC = 4cm
10^oC = 2.6cm

Are you certain that the gas was at 5C, 25C, etc.? It is very difficult to hold something at a specific temperature like that. With 0C, you can put it into a bath of melting ice, or with 100C, boiling water- water will stay at those temperatures as long as there is still some ice or water left. One other temperature you can be sure of is "room temperature"- let the object sit for an extended period, then measure the temperature of the air. Water does not "stay" at other temperatures.
T 11:39 AM

Well the capillary tube's wall was very very thin and I read the level of the oil while it was still in the water. So I assurmed that the temperatures would have equalized by the time I recorded the result.