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The data should give straight-line graphs, although there may be a need to discuss the uncertainties in the readings.Students need to appreciate that the way the length of column changes reveals how the volume of the air alters ( volume = length x cross-sectional area).Repeat for about four more temperatures, plotting the graph as the experiment proceeds.Record the temperature and length of the air column.Add water, or water and crushed ice, to the beaker, always ensuring the trapped air column is under the surface of the water in the beaker.
CONSTANT PRESSURE GAS THERMOMETER BOILING POINT FREE
Put the tubes into the deep beakers with the open end free to the air.
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Measurements are easier if the end of the air column inside the tube coincides with the zero of the centimetre scale on the rule. Fix the capillary tube and thermometer to the ruler with rubber bands at each end.If you do not like working with acid, the experiment could be tried with an oil plug but the water vapour pressure in the air column would then distort the results. Sulphuric acid is hydrophilic it removes water vapour from the air trapped in the capillary tube. If a laboratory oven is available, the tubes can be heated to 120☌ for about 20 minutes instead of using brine. The index will be drawn to a suitable position just over halfway along. Whilst hot, dip the open end of each tube into a small beaker containing concentrated sulfuric acid, so that a 5 mm length of acid is drawn in to the tube as it cools.This will ensure that the tubes are dry internally as well as hot. Put all the tubes into a deep beaker of strong brine and bring it to the boil.The capillary tubes should be about 20 cm long and 1 mm bore, closed at one end and open at the other. The beaker should be deep enough for all the air column in the tube to be immersed in water. If suppliers will not stock it, this experiment could be omitted. It is almost impossible to obtain tubing with this bore and not a very thick wall: 3 mm outer diameter and 1 mm inner diameter is ideal. Read our standard health & safety guidance Take care when handling concentrated sulfuric acid. When you seal the tubes, avoid a long taper at the end. Capillary tube with liquid index (see technical note).This experiment was safety-tested in August 2006Įxpansion of air at constant pressure and an indication of absolute zero (-273☌). Plunging the flask into hot water may increase the volume of the gas so much that either the oil plug flies out of the tube, or it breaks up and runs down the inside of the tube.The pressure exerted by the gas will therefore increase. If the temperature of the container is raised, molecules move faster. Students may already know that a gas is made up of rapidly moving molecules which hit the surfaces of the container and exert a force on the container so creating a pressure.
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The volume expansion of a gas is approximately 500 times that of glass, so it is unlikely that the expansion of the flask will have any noticeable effect.