Analysis of a Chemical Mixture Using the Ideal Gas Law
The objective of this experiment was to determine the composition of the NaNO2 mixture in the net ionic reaction of NO2-(aq) + HSO3NH2(aq) > HSO4-(aq) + H2O(l) + N2(g) in unknown mixture number nine.
It was known that NO2-(aq) and HSO3NH2(aq) were in a stoichiometric 1:1 molar ratio. In trial one the percent mass of NaNO2 in the unknown mixture was 59. 30%. In trial two, the percent mass of NaNO2 was 63. 47%.
Lastly in trial three, it was determined that the percent mass of NaNO2 was 60. 11%.Based on these results the average percent mass of the NaNO2 was 60. 96% with a standard deviation of 2. 209. Lastly, the percent relative standard deviation was determined to be 3.
623. Thus, the percent precision was found to be 96. 38% suggesting that the process used to determine these results was fairly consistent. Due to the varying results in the three trials, it can be assumed that there was random experimental error. Specifically, trial one still had air bubbles in the dram vial inside the Erlenmeyer flask when the ending volume of N2 gas was recorded.The experimenter shaking and swirling the flask stopped prematurely believing that the reaction was complete.
Since all the gas bubbles weren’t released, the gas pressure wasn’t completely accurate. With excess gas still remaining in the Erlenmeyer flask, the meniscus level was higher on the measuring tube than it should have been. Thus, the recorded value for the volume of N2 gas collected was less than it was actually supposed to be. Therefore, the calculated molar content of N2 gas was lower than it should have been, thus affecting the calculated amount of NaNO2 based on the 1:1 molar ratio.Therefore, this trial had a lower calculated percent mass of NaNO2 in the unknown mixture than it should have had. Trial two also consisted of a random experimental error.
It was observed that there were liquid condensation particles clinging to the sides of the measuring tube when the ending volume of N2 gas was recorded. These liquid particles are due to the nature of the exothermic reaction taking place in the Erlenmeyer flask. The presence of the condensation particles increased the change in volume for this trial.This increased the calculated amount of moles of N2 gas, thus also the amount of calculated moles of NaNO2 because of the 1:1 molar ratio. Therefore, a higher mass percentage of NaNO2 in the unknown mixture was calculated for this trial. If the partial pressure of water was ignored in the calculations, then the pressure used in the PV=nRT equation would simply be the atmospheric pressure.
Without factoring in the vapor pressure, the pressure used in this equation would be higher than it should be.Therefore, solving for n, the moles of N2 gas, would produce a higher molar content. With a higher molar content of N2 gas, a higher percentage of NaNO2 would be calculated. If the amount of sulfamic acid added to the reaction was doubled, then the percentage of NaNO2 should be unaffected. Since NaNO2 is the limiting reactant, it determines the amount of moles of products produced. Sulfamic acid is the excess reactant, thus if its molar content were doubled in this reaction, there would be no effect on the production of N2 gas.
