Experiment 9: The Molar Volume of a Gas Introduction Description:
The purpose of this experiment was to determine the molar volume of a gas by conducting the hydrogen gas producing chemical reaction:
Mg(s)+2HCl (aq)→〖MgCl〗_2 (aq)+H_2 (g)
A known mass of solid magnesium was reacted with an excess of hydrochloric acid in a sealed vessel, three times, for a total of three trials. A gas pressure sensor and temperature probe were connected to the vessel and a computer which allowed Logger Pro to collect the pressure and temperature change data through the course of the reaction. This data was then used to calculate the molar volume of the hydrogen gas at STP, and the Universal Gas Constant, R, for each trial. Background:
STP stands for
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The ideal gas law, followed by a mole ratio were then used to calculate the volume of one mol of H_2 at ambient conditions. After that, the combined gas law was used to calculate the volume of one mol of H_2 at STP. Before calculating the experimental gas constant, the volume of air space in the flask was calculated, using the volume of empty air space in the flask and the 5 mL of HCl. Result calculations for all trials are shown in “Table 2”.
(0.0107 g Mg)/1×(1 mol Mg)/(24.305 g Mg)=(4.40×〖10〗^(-4) mol Mg)/1×(1 mol H_2)/(1 mol Mg)=4.40×〖10〗^(-4) mol H_2 23.63 ̊C + 273.15 K = 296.78 K
(8.1 kPa)/1×(1 atm)/(101.325 kPa)=0.0799
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The percent error compared to an ideal gas at STP (22.4 L) would then be: (22.43-22.4)/22.4×100=0.13%. These values compare well, meaning that little experimental error occurred during this part of the experiment. The universal gas constant for trial 3, turned out to be: 0.08199 (atm*L)/(mol*K). Compared with the ideal gas constant: 0.08206 (atm*L)/(K*mol), the percent error turned out to be 0.09% (above under “Trial 3 Calculations”). Thus, the value that was calculated from the experimental data was very close to the ideal constant, meaning again, little experimental error occurred during this part of the