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Percent

By triciafishanna Oct 23, 2014 820 Words

Experiment 7:
Percentage Composition of Kclo3- A Gas law Experiment
Anna CunananProfessor Stewart
Chemistry 400 T/TH 1:30 PM
18 March, 2014
Objectives: In this Experiment, we will be decomposing KClO3 into two different compounds, KCl and O2. We are given a known mixture that has MnO2 in it to act as a catalyst. When decomposing KClO3 it releases O2 gas, which we then collect into the Erlenmeyer flask. The gas then displaces the water into the beaker, which we can then calculate the water evolved. The first method we use to determine the percent composition is Gravimetric. With this method we use the mass of the reactant and the mass of the product. Another way to acquire the percent composition is by the Volumetric Method. This method requires measuring the water displaced by the O2 gas. If the experiment is done correctly, we should be able to calculate the percent composition of KClO3 by using both methods. Theory: This experiment requires us to use both the Gravimetric and Volumetric methods in order to acquire our percent composition. Since all gasses at Standard Temperature and Pressure contain one mole for every 22.4 L of gas, we can use stoichiometry to figure out how many moles of reactant we began with. Considering the room is at constant temperature change, the volume of the gas varies. Thus we convert the volume of gas used to STP conditions. Procedure:All means and materials were conducted as advised accordingly to Experiment 6 found on pages 55-60 of the Fall 2013-2014 Lab Manual for Professor Stewart’s Chem 400 class. Data Analysis:Gravimetric Data Table:

Mass of empty Test Tube 16.5793 g 16.9237 g 16.9013 g
Mass of Test tube & Sample (before) 18.5793 g 18.9772 g 18.9072 g Mass of Test tube & residue (after) 17.8735 g 18.2414 g 18.1887 g Gravimetric Data Table- Calculated Stoichiometry

Mass of Sample mixture 2.000g 2.0535g 2.059g
Mass of O2 evolved 0.7238 g 0.7358 g 0.7285 g
Moles of O2 evolved 0.0226 moles .02299 moles .02278 moles
Moles of KClO3 decomposed 0.0678 moles 0.0690 moles 0.0666 moles Mass of KClO3 in Sample 1.8466 g 1.8785 g 1.8613 g
Percent of KClO3 in sample 92.33 % 91.48 % 90.40%
Percent Error 2.33% 1.48% 0.40%

Gas Law Data TableVolume Data-
Mass of Empty Beaker 407.00 g 407.85g 407.55 g
Mass of beaker + H2O 942.56 g 958.74 g 958.89 g
Density of water .99792 g/ml .997882 g/ml .997926 g/ml
Volume of H2O displaced 535.560 g 551.26 g 551.43 g
Pressure Data
Atm. Pressure 770 torr769.5 torr769.5 torrBarometer Temperature 23.98 C 23.90 C 23.80 C Vapor Pressure of H2O 22.303 torr22.243 torr22.110 torrTemperature Data Temperature of O2 Gas 21.9 C 21.5 C 21.3 C

Gas Law Data Table- CalculatedConcerning Gas Law
Mass of H2O collected 535.560 g 551.26 g 551.43 g
Volume of H2O collected (density) 0.99792 g/ml 0.997882 g/ml 0.997926 g/ml Volume of O2 evolved at exp. Conditions 0.5420 g/L 0.5495 g/L 0.5422 g/L Pressure due to O2 alone 770 torr769.5 torr769.5 torrVolume of O2 corrected to STP 0.5062 g/L 0.5150 g/L 0.5103 g/L Moles of O2 evolved (22 not 6) 0.0158 moles 0.0161 moles 0.0160 moles Concerning Stoichiometry

Moles of KClO3 decomposed 0.0105 moles 0.0107 moles 0.0107 moles Mass of KClO3 1.2910 g 1.3155 g 1.3073 g
Mass of sample mixture (original) 2.000 g 2.0535 g 2.0059 g
% of KClO3 in sample (exp) 64.55% 64.06% 65.17%
% of KClO3 in sample (theoretical) 90% 90% 90%
Percentage Error 25.45% 25.94% 24.83%
Summary Table of Results
90% sample Gravimetric Method 92.33% 91.48% 90.40% 2.33% 1.48% 0.40% Volumetric Method 64.55% 64.06% 65.17% 25.45% 25.94% 24.83%
Conclusion:Though many errors could have happened, the main two errors would have been not properly sealing the apparatus to an air tight standard and not decomposing the Potassium Chlorate to its full potential. Taking into account these errors, if the apparatus was not sealed air tight, some of the O2 gas could have been released this not displacing the correct amount of water. If this were to occur, the gravimetric data would result in lower values than expected. Whereas if the Potassium Chlorate was not properly dissolved, we would have shorted the gas displacement also resulting in a lower value than expected. When comparing both methods to calculate our percent error, the Gravimetric Method seemed closer to the 90% we were aiming for. My Confidence lies in the Gravimetric Method. Though my Volumetric Methods percentage error was higher, it could be due to many reasons. One being that my calculations could be off and another because the seal might not have been air tight. If the apparatus was not sealed properly, we could have possibly lost some of our O2 gas resulting in a high percent error. All in all I am confident in my experiment because I presented skills needed to acquire the percent error of Potassium Chlorate.

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