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Old Sep 22nd 2017, 07:01 PM   #1
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Exclamation Green Chemistry (Gas Stoichiometry)

For my chemistry lab, I reacted Mg powder with HCl to create H2 gas. I measured the volume of H2 gas created by salt water displacement by reading off an inverted test tube. I measured 14.0 mL and calculated the percent yield (used PV=nRT to find theoretical volume and divided it by the actual- 0.014L volume) which was 62.2%.

The next question that makes no sense is: "If you did not get 100% yield, could this be explained by the temperature of the gas? If so, given the yield you observed do you expect the gas temperature might have been above or below the temperature recorded for the salt bath water (the thermometer states 290 K)." Hint was to use ideal gas law and see volume of H2 gas in relation to gas temperature.

Based on my interpretation, the percent yield has nothing to do with the temperature of the gas produced. And by calculating the number of moles of H2 gas produced (using PV=nRT I got 5.9*10^-4 mol) and plugging into the PV=nRT equation, everything cancels out and I get 290K, which makes the gas temperature the same as the salt water temperature. I don't think this reaction involves equilibrium either.

Generally confused on how I should answer this. Should I say that the temperature of the gas is higher than the salt bath, and since temperature is directly proportional to volume, higher temperature (when compared to 'initial' temperature of salt water bath) would yield more volume of H2 gas, which was what we observed.

Please help me out in any way!
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atom economy, gas law, percentage yield

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