Charles' Law

Introduction

This procedure uses the air trapped inside of a Beral pipet at different temperatures to demonstrate Charles' Law. In order to do this, we must assume that a constant pressure is exerted by equal depths of hot and cold water and that that pressure causes no significant distortion of a Beral pipet.

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Procedure
  1. Attach a weight or metal strip to a dry, pulled, Beral pipet and attach a string to this assembly. Lower this assembly into a 250mL (or larger) beaker of hot water (temperature should not be in excess of 80 °C as this can cause some distortion of the pipet bulb). Keep the string out of the water to make removal of the assembly easier.
  2. Allow this to remain under water until bubbles cease to emerge from the tip. Read and record the temperature of the hot water bath (Th). Remove the pipet from the hot water bath and instantly place it into ice water. Allow sufficient time for it to cool and for water to enter the pipet. Read and record the temperature of the cold water bath (Tc).
  3. Remove the pipet from the water and carefully count drops of water which have entered the pipet during cooling (Cold drops). Completely fill the pipet and count how many drops are contained in the full pipet (Total drops).
  4. (Tc+273)/(Th+273) = (Total drops-Cold drops)/(Total drops)
  5. Remove the beaker of water from the hot plate. Repeat the experiment at lower temperatures for the hot water bath.

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Data Analysis

Temperature = 61° (hot) 25° (cold)
Total drops = 198
Cold drops = 33
( 25 + 273 )/( 61 + 273 ) = ( 198 - 33) /(198 )
( 298 / 334 ) = ( 165 / 198 )
0.89 = 0.83

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Safety

Hot plates and hot water can cause burns. Handle hot materials with caution.

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TG Discussion

Loss of heat when transferring between hot and cold containers (trial in the same container yielded 0.89 = 0.87); loss of water by squeezing pipet accidentally; distortion of the pipet's shape; and moisture in pipet to begin with are all possible sources of error in this experiment. Counting the large number of drops in a filled pipet is tedious and, therefore, error prone.

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TG Materials

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TG Reference


The microscale version of this lesson was developed by:

Dennis Miller
Bassett HS
Bassett, NE

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