3 The gas you used in this experiment was a mixture rather than a pure substance
ID: 1042187 • Letter: 3
Question
3 The gas you used in this experiment was a mixture rather than a pure substance. Explain why this should have no effect on your results. 4 For Charles' Law to apply, conditions other than temperature and volume (e.g., pressure and quantity of a gas) must be kept constant. When you heated the experimental chamber in the boiling-water bath, the bubbles emerging from the tube into the reservoir indicated that both the pressure and the quantity of gas in the experimental chamber were changing. Explain why these changes in pressure and gas quantity did not affect your Charles Law experiment.Explanation / Answer
Solution:
3. We have assumed the gases to be ideal and for a mixture of ideal gas, one mole of any ideal gas occupies the same volume under similar conditions of pressure and temperature. This is according to the ideal gas equation:
PV = nRT
So, if all the gases are ideal, then the properties of such sample are independent of the nature of gases taken. This is also true because of the following assumption for ideal gases: There exists no intermolecular forces of attraction or replusion between ideal gas molecules. Since the molecules don't interact with each other, therefore it does not matter whether we take 1 gas or a mixture. The entire mixture will behave as one ideal gas.
4. It is absolutely true that for Charle's law to apply, pressure and quantity of gas should be constant but for experimental verification of charle's law, we just need to prove that gases expand on heating and the volume is directly proportional to the absolute temperature.
In our current experiment, when we heated the gas, the gas tried to expand. This also caused an increase in pressure. Now, since the overall setup is neither rigid nor closed, the increase in pressure was nullified with some loss in amount of moles to the surroundings through water. So, to keep the pressure constant, some moles were lost to the surroundings and hence both these changes (Pressure and quantity) acted against each other. Overall, this has happened because the gas tried to expand on heating which is true according to charle's law.
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