Last week we looked at Boyle’s law  – holding a sample of gas at constant temperature while varying the pressure and watching the volume change.  Today we investigated Charles’ Law by keeping the pressure constant and changing the temperature so we could see how the volume would vary.  We used the same 10ml syringes that we used last week but tried to do a better job lubricating the plungers with vegetable oil.  They still seem to get stuck so the students gave them a bit of push/pull/twist to free them and then measured where the plunger came to rest.

img_6574The lab is from the Home Scientist Chemistry kit manual, CK01A, Session VIII-2: Observe the Volume-Temperature Relationship of Gases (Charles’ Law).  To get a range of temperatures we put the syringes and thermometers in my kitchen freezer which got us to -12C,  an ice/water bath, boiling water and cups of water heated in the microwave to get a few points in between.  The students made sure to reset the syringe before each data point and the results of this experiment came out much better than last weeks.  The data analysis was a lot easier in this lab since the only math was converting their measured temperatures in Celsius to Kelvin.   You can see from one set of results below that the data came out very linear, as you increase the temperature of a gas the volume goes up as expected.  Since this was a relatively short lab I talked about percent error a bit before we started and showed them how to put error bars on their data points.  I also had the students graph their data as they went so they could see what temperatures they might want to do to fill in gaps in their graph.  This also allowed them to see when something might have gone wrong (plunger stuck) and they needed to retake a data point.

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If I only had time for one of these gas law experiments I would definitely recommend this one over the Boyle’s law lab.

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