Experiment 6 – Decomposition of Potassium Chlorate , Lab Reports of Chemistry

Download Experiment 6 – Decomposition of Potassium Chlorate and more Lab Reports Chemistry in PDF only on Docsity! Name: _________________________________ Section: _____________________ Chemistry M12 Laboratory Manual Page 27 Experiment 6 – Decomposition of Potassium Chlorate Discussion The percentage composition of a compound is the percent by mass of each element in the compound. This can be theoretically calculated using atomic masses found on the periodic table, and experimentally calculated from lab data. The percent composition is calculated by taking the mass of the part divided by the mass of the whole times 100. In this experiment, solid potassium chlorate will be strongly heated. This causes it to decompose into solid potassium chloride and oxygen gas. The relative amount of potassium chloride (residue left behind) and oxygen gas (mass lost) are experimentally measured and compared to the theoretical values. Percent error is calculated by finding the absolute value of the difference between the theoretical and experimental values and dividing that number by the “true” theoretical value and last multiplying the answer by 100. Following the quantitative test, we will perform a qualitative test on the residue and known compounds of KClO3 and KCl using silver nitrate solution. AgNO3 solution is used as a general test for chloride ions. A positive test forms white solid AgCl and indicates the presence of Cl– ions in a solution. Tap water contains chloride ions, so it is very important to perform this test with clean equipment that has been rinsed out with deionized water and to use deionized water in the test. To obtain accurate and precise data you should do the following: 1. Use the same balance for all mass measurements. 2. Record data directly and immediately into the lab report. 3. Record data completely (to the nearest 0.001 g); do not round off the data. 4. If an error is made in data collection, do not scratch out or erase but simply draw a single line through the error and write the correction beside it. 5. Duplicate samples should be analyzed so that results can be compared and averaged. 6. Handle the crucibles with tongs not fingers. 7. The crucible must be covered while heating to avoid any loss due to splatter. Name: _________________________________ Section: _____________________ Chemistry M12 Laboratory Manual Page 28 Procedure A. Quantitative Determination of Percent Composition 1. Weigh a clean dry crucible and cover to the highest precision. Be sure that you use the same balance for all mass measurements within the same experiment to cancel out systematic errors. 2. Carefully read the label on the container and add between 1.0 to 1.5 grams of potassium chlorate, KClO3, into the crucible and cover and weigh to the highest precision. NOTE: In part B of this lab, we will be using some potassium chloride. If you accidentally place KCl in your crucible, no mass will be lost on heating and you will have to start over and repeat the experiment correctly using KClO3! 3. To a ring stand, attach a ring and place a clay triangle on the ring. Place the crucible with cover on the clay. Very gently heat with a Bunsen burner for about 8 minutes. Readjust the flame and continue heating more intensely now so that the bottom of the crucible glows red for another 10 minutes. 4. After this two step heating process (1st heating) is complete, turn off the burner, close the crucible lid, and allow to cool about 10 minutes before weighing. It is important to have all mass measurements made at or near room temperature. Do not transfer the hot crucible to the tabletop; it is too hot and will permanently mark the table. Use the crucible cooling plates that are provided. Weigh your sample. The cooling period is a great time to start the second sample. 5. Heat the covered crucible and contents another 6 minutes at maximum temperature, then cool and reweigh (2nd heating). If the results agree within +0.050 g, you are done and will not need to have a 3rd heating. If the difference is greater than 0.050 g, repeat the heating for another 6 minutes (3rd heating). B. Qualitative Examination of the Residue 1. Place three clean test tubes in a rack. Put a pea sized quantity of KCl in test tube number 1 and a pea sized quantity of KClO3 in the test tube number 2. Add 10 ml of deionized water to each and mix. Next, add 10 ml of deionized water to your residue in the crucible, mix, and transfer a portion to test tube number 3. NOTE: It is not necessary to dissolve and transfer the entire residue. 2. Add 3 drops of 6 M HNO3 and 5 drops of 0.1 M AgNO3 solution to each test tube. Record observations. DISPOSE of solutions and precipitates containing silver in the waste container provided.