Stoichiometry
Rebekah Muller
Chemistry Lab 101-02
Instructor: Sam Stevenson

Abstract: Stoichiometry is used to figure out how much potassium chlorate in a mixture of potassium chlorate and an inert substance (a substance that does not react chemically). By determining the mass of the product experimentally, the mass percent composition is calculated stoichometrically. After finding the mass percent composition, the final calculation to find is percent error (with the accepted value given). In this experiment, we use a solid that contains potassium chlorate as the reactant and then determine how much potassium chlorate was actually in the solid. To determine the amount of potassium chlorate, we heat up the solid on a Bunsen burner and measure how the solid as changed while the reaction was taking place.
Objective:
There are four objectives to this lab: to calculate the theoretical and percent yields, predict the effect of experimental error on percent yield, calculate the percent composition, and calculate the percent error.
Introduction:
The purpose of this lab is to determine the mass percent composition of potassium chlorate in an unknown substance by using Stoichiometry. Stoichiometry is the calculation of the quantities of chemical elements or compounds involved in chemical reactions. In this lab, the decomposition of the reaction would further the calculations of potassium chlorate in the mixture. Decomposition means the breaking down of compounds or mixtures into the form of elements or smaller substances. The hypothesis trying to be proven is that it is possible is find the mass of a compound can be determined through Stoichiometry and experimentally. Experimentally, the mixture will be heated. If the heating continues for an extended amount of time, the reaction will not be affected because the reaction has already been completed.
Results:
The results data table is connected on another page.
Discussion:
In order to calculate the percent composition, the amount of oxygen after decomposition needed to be measured. Trial one measured .24 grams of oxygen had precipitated. These .24 grams of oxygen were converted to moles of oxygen by the use of molar mass (18 grams per mole). By using the mole to mole ratio for potassium chlorate to oxygen and molar mass of potassium chlorate, the amount of potassium chlorate was calculated to be .613 grams. The percent composition was then found by dividing the found amount of potassium chlorate by the amount of potassium chlorate put into the cylinder before decomposition take place (1.036 for trial one). The quotient of the problem needs to be multiplied 100 percent and the product will be the percent composition of the potassium chlorate for that specific trial. The percent compositions for all three trials were 59.2%, 72.7%, and 70.0% respectively. To find the percent error, the percent composition found for each trial and the given value percent composition was used. The absolute value of the computed value the given, divided by the given. After obtaining this value, the value should be multiplied by 100 percent to get the percent error. Each percent error ended up different for each trial: trial one=15.43%, trial two=3.86% and trial three=.43%. All three trials’ percent error was below 25% meaning that the results from the trials were fairly accurate for each trial. Throughout the experiment there were possible sources of error. Random error is error in measurement that leads to measurable values being inconsistent when repeated measures of a constant attribute or quantity are taken. Systematic error is biases in measurement which lead to the situation where the mean of many separate measurements differs significantly from the actual value of the measured attribute. One source of error would be the drying process. Instead of drying the test tube over the Bunsen burner, drying the test tube with a paper towel could leave behind particles that could potentially change the results of the experiment if the particles catch on fire. Another possible source of error is if the reaction does not completely take place. If the reaction did not completely take place, the amount of oxygen that evolved would decrease because not all of the potassium chlorate reacted during the procedure. These errors could be avoided by taking the time to dry the test tube. Even when the test tube looks dry, take another minute to be cautious of the fact that it may not be completely dry. To avoid the error of not having the reaction fully take place, use pre-caution as before. If the reaction was heated for a longer period of time, there would be certainty that the full reaction had taken place. By using the same amount of the mixture after the oxygen has been combusted then the oxygen amount would stay the same regardless of the amount of time.
Conclusion:
Once completing the experiment, the calculations were carried out. By taking the average of the percent errors from each trial, it can be concluded that with such a low percent error the data is quite accurate.
Experimental:
To begin the experiment, first two test tubes must be thoroughly cleaned with distilled water; and then turn on the Bunsen burner. Use the burner to dry the test tube. Hold the test tube about one inch above the flame. (DO NOT DRY THE TEST TUBE USING A PAPER TOWEL!!!) Once the test tubes dried, the experiment is ready to take place. This experiment required three trials used one gram of the unknown sample for each trial. Determine the weight of the test tube and the amount of the sample before conducting each trial. Put the sample into the test tube and hold the test tube over the Bunsen burner for about five minutes to ensure that the reaction has completely taken place. Then determine the new weight of the test tube with the sample still in the test tube. Collect data in an organized fashion or data table. Conduct three trials to lessen the amount of error. After carrying out three trials, clean up and leave the lab area exactly how it was found.

*no references were used in the writing of this paper*