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What are two precautions you must observe  when using the electronic balance?

What are two precautions you must observe  when using the electronic balance?

Chemistry
Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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In Part A you will be performing several mass measurements. What are two precautions you must observe 
when using the electronic balance?

Part A: Mass Percent of Oxygen in Potassium Chlorate The following steps should be carried out for two separate samples of potassium chlorate. 1. Clean both crucibles and their lids (obtained from the stockroom) by thoroughly rinsing with distilled water then drying as completely as possible with a paper towel. 2. Weigh the first crucible and lid on an electronic balance and record this mass on your report form. 3. Add approximately 1 gram of potassium chlorate to the crucible. Do not do this over the balance! Then weigh and record the mass of the crucible, lid and potassium chlorate sample. 4. Fetch a stand and ring clamp from the back of the lab. As shown in the figure and photo on the following page, place your clay triangle on the ring, and then place the crucible containing the sample onto the triangle. Cover the crucible with the lid. 5. Using a Bunsen burner, heat the crucible and sample for a total of 12 minutes. Be sure that the crucible is covered, and that that the top of the flame is touching the bottom of the crucible. • For the first 6 minutes, the sample should be gently heated by adjusting the Bunsen burner flame to a low-moderate temperature. Note that heating the sample too intensely at this point could cause loss of the sample via splattering, and could crack the crucible. • For the last 6 minutes, the sample should be strongly heated by adjusting the Bunsen burner flame to a high temperature. 6. Allow the crucible to cool to room temperature. Then weigh and record the mass of the crucible, lid, plus the residue that remains. Note that the weight of your sample is expected to decrease by at least 30% of its original mass (~0.3 g). 7. Now heat the sample a second time for an additional 6 minutes using a high temperature flame. Then, once again, allow it to cool to room temperature. Weigh the cooled crucible, lid and sample after this second heating and record the mass. If this mass is within 0.050 grams of your mass measurement after the first heating (see step 6), no further heating is necessary and you may begin Part B. Do not dispose of the residue as you will need it for Part B. 8. If the sample from step 7 is not within 0.050 grams of the mass from step 6, heat again for a third time, cool and record the mass. 9. Repeat all steps for your second crucible and second sample of potassium chlorate. 10. Analysis: For each sample analyzed, obtain the mass of potassium chlorate before heating, the mass of KCl residue after heating, and the mass of oxygen released. Use the residue mass after the final heating for these calculations. Then using these values, determine the experimental mass percent of oxygen in potassium chlorate (see Theory Section for equation required).
Transcribed Image Text:Part A: Mass Percent of Oxygen in Potassium Chlorate The following steps should be carried out for two separate samples of potassium chlorate. 1. Clean both crucibles and their lids (obtained from the stockroom) by thoroughly rinsing with distilled water then drying as completely as possible with a paper towel. 2. Weigh the first crucible and lid on an electronic balance and record this mass on your report form. 3. Add approximately 1 gram of potassium chlorate to the crucible. Do not do this over the balance! Then weigh and record the mass of the crucible, lid and potassium chlorate sample. 4. Fetch a stand and ring clamp from the back of the lab. As shown in the figure and photo on the following page, place your clay triangle on the ring, and then place the crucible containing the sample onto the triangle. Cover the crucible with the lid. 5. Using a Bunsen burner, heat the crucible and sample for a total of 12 minutes. Be sure that the crucible is covered, and that that the top of the flame is touching the bottom of the crucible. • For the first 6 minutes, the sample should be gently heated by adjusting the Bunsen burner flame to a low-moderate temperature. Note that heating the sample too intensely at this point could cause loss of the sample via splattering, and could crack the crucible. • For the last 6 minutes, the sample should be strongly heated by adjusting the Bunsen burner flame to a high temperature. 6. Allow the crucible to cool to room temperature. Then weigh and record the mass of the crucible, lid, plus the residue that remains. Note that the weight of your sample is expected to decrease by at least 30% of its original mass (~0.3 g). 7. Now heat the sample a second time for an additional 6 minutes using a high temperature flame. Then, once again, allow it to cool to room temperature. Weigh the cooled crucible, lid and sample after this second heating and record the mass. If this mass is within 0.050 grams of your mass measurement after the first heating (see step 6), no further heating is necessary and you may begin Part B. Do not dispose of the residue as you will need it for Part B. 8. If the sample from step 7 is not within 0.050 grams of the mass from step 6, heat again for a third time, cool and record the mass. 9. Repeat all steps for your second crucible and second sample of potassium chlorate. 10. Analysis: For each sample analyzed, obtain the mass of potassium chlorate before heating, the mass of KCl residue after heating, and the mass of oxygen released. Use the residue mass after the final heating for these calculations. Then using these values, determine the experimental mass percent of oxygen in potassium chlorate (see Theory Section for equation required).
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