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Materials
- Frame for complete experiments 45500.00
- Rear cover for complete experiment panel 45501.00
- Panel for complete experimental set-ups 45510.00
- Clamping holder, d = 18...25 mm 45520.00
- Clamping holder, d = 8...10 mm, turnable 45522.00
- Apparatus carrier with fixing magnets 45525.00
- Holder for glass jacket 45524.00
- on fix. magn. 02161.00 Holder for hand-held instruments
- Clamp on holder for demonstration board 02164.00
- Spring plugs, 50 pieces 45530.00
- G-clamp 02014.00
- Cobra3 DISPLAY UNIT 12154.00
- Support clamp for small casings 02043.10 - l = 250 mm 02031.00 Support rod, stainless steel 18/8, - Data cable RS 232, Sub-D/USB 07157.01 - Cobra3 power supply 12151.99 - Hand held instrument 2 x NiCr-Ni, RS 232 07140.00 - Immersion probe NiCr-Ni, stainless steel 13615.03 - RS 232 07136.00 Hand held measuring instrument pressure, - Pressure sensor, 1.0...1300 hPa 07136.01 - Glass jacket 02615.00 - Gas syringe, 100 ml 02614.00 - Erlenmeyer flask, DURAN, 100 ml, GL 25 35844.15 - Heating apparatus 32246.93 - Magnetic stirring rod, cylindrical, l = 30 mm 46299.02 - Magnet rod, l = 200 mm, d = 10 mm 06311.00 - 1.
- Fig. The Gas Laws
Silicone tubing, d = 3 mm 39292.00 1 Rubber tubing, d = 6 mm 39282.00 1 Rubber caps, pack of 20 (1 only) 02615.03 1 Glass tube, straight, l = 80 mm 36701.65 1 Hose clips made of stainless steel, d = 5-12 mm 40997.00 2 Funnel, glass, d = 80 mm 34459.00 1 Beaker, DURAN, tall form, 250 ml 36004.00 1 Motor oil
Safety measures Waste motor oil must be disposed of according to the appropriate regulations. It is obligatory to use the spring plugs supplied to firmly secure the holder for the glass jacket in position.
Preparation Gas syringes are not completely airtight. This is of no importance for most applications. In cases of large pres- sure differences to the surroundings, however, this would result in falsification of the experimental results due to a passage of gas, e.g. from the inside of the syringe to the surroundings. To improve the sealing, just a few drops of commercially available multirange motor oil (e.g. 5W40) are required. Drop them onto the sliding area of the plunger and use this to distribute them uniformly in the
syringe. Take care when doing this that a clear oil film is formed, without streaks and air inclusions between the plunger and the body of the syringe. Motor oil is more suit- able than thinly-liquid paraffin oil at high temperatures, and also than the more viscous silicone oil. Furthermore, it is easier to remove from the syringe.Gas syringes prepared in this way are stable over long-term storage, and can be used time and again.
Set-up Position the clamping holders on the panel for complete experiments as shown in Fig. 2, and subsequently fix the assembled apparatus to it as shown in Fig. 1. Fit the gas syringe in the glass jacket (follow the instruc- tions supplied with the glass jacket to do this). Seal the left socket of the glass jacket with a closing cap. Fit rubber tub- ing to the hose nipple of the vertical socket and position the free end in the Erlenmeyer flask. This serves as a water overflow. To ensure pressure equalisation, remove the sealing ring from the cap of the Erlenmeyer flask. Fill water through the right vertical socket into the glass jacket, and also insert a magnetic stirrer. Subsequent to this, fit the immersion probe for temperature measurement into the socket as follows: First pierce a rubber cap with a needle and ease the immersion probe through the perforation. Then fit the cap on the end of a short glass tube and insert
The Gas Laws
Fig. 2
2. Gay-Lussac’s law and Amonton’s law The values given are corrected values here also (see above). The pairs of values listed in the Tables below which were experimentally determined have been plotted in Figs. 4 and 5.
Explanation Boyle’ law can be derived from the first part of the experi- ment: At constant temperature, the product of volume and pres- sure is also a constant. This enables the volume of a por- tion of gas to be calculated after an increase in pressure, as long as the temperature remains constant. The follow- ing relationship is valid:
V 1 · p 1 = V 2 · p 2 ,when T = constant
From the second part of the experiment, the following two laws can be derived:
At constant pressure, the volume of a gas is directly pro- portional to the absolute temperature (Gay-Lussac’s law). At constant volume, the pressure of a gas is directly pro- portional to the absolute temperature (Amonton’s law). we therefore have:
V 1 / V 2 = T 1 / T 2 , where p = constant
and:
p 1 / p 2 = T 1 / T 2 , where V = constant
Taken Avogadro’s law into consideration, the ideal gas law can be derived from the three experimentally determined laws. A simple combination of the gas laws gives the gen- eral gas equation:
V 0 = (V · p · T 0 ) / (T · p 0 )
where: T 0 = 273 K and p 0 = 1013 hPa
The Gas Laws
Heating Cooling T / K T / °C p / hPa V / ml p / hPa V / ml T / K T / °C at V = const. at p = const. at V = const. at p = const. 295.6 22.4 1003 51.5 1258 64.5 368.2 95. 314.7 41.5 1071 55.0 1234 63.0 358.2 85. 330.4 57.2 1121 57.5 1199 61.0 348.2 75. 340.5 67.3 1162 59.5 1160 59.5 338.2 65. 351.2 78.0 1196 61.0 1131 58.0 328.2 55. 360.4 87.2 1231 63.0 1088 56.0 318.2 45. 373.1 99.9 1274 65.0 1055 54.0 308.2 35.
Table
Fig. 4: A plot of volume against temperature at constant pressure (measured values with best straight line)
Fig. 5: A plot of pressure against temperature at constant volume (measured values with best straight line)
Notes Time is the reason for combining the derivations of the laws of Gay-Lussac and Amonton in a single experimental set-up. The accuracy of the results of the measurements suffers because of this. Their derivation in separate exper- iments is described in detail in the PHYWE literature, “Natural Science with Cobra3”, part 5, CD5 5.1 to CD5 5.4. When Cobra3 is used instead of the hand-held measuring instruments, measured values can be transmitted directly to a PC for evaluation. The cooling curve is particularly suitable for this! Separate set-ups for Gay-Lussac’s law and Amonton’s law are then necessary, however. This experiment is extremely suitable as an introduction to the use of computers for the evaluation of complex con-
nections in natural science lessons. The graphical evalua- tion of the measured values, for example, can be very sim- ply carried out using “measure” software. This software is license-free for the purpose of evaluating and graphically representing measured values (freeware). It is available as download-file under URL “www.phywe.de”, or can be installed from the demo-CD supplied with each Phywe hand-held measuring instrument. Figures 3, 4 and 5 were created with this software. For this, the students should have some knowledge on working with computers, and optimally also on “measure” (see the previous note on lit- erature).
The Gas Laws
