Stoichiometry Lab Report

Transcription

1 Stoichiometry Lab Report Touche G10 Variables Variable Dependent Controlled: Amount of NaHCO3 Theoretical Yield Vinegar Evaporation Manipulation We measure the remaining NaC 2 H 3 O 2 and compare it with the theoretical yield. 4.5 grams of NaHCO grams of NaC 2 H 3 O 2 Use the same brand of vinegar Use the same method of evaporation Hypothesis If we put moles of NaHCO 3 in excess with vinegar (HC 2 H3O 2 ) and boil it, we would get grams of NaC 2 H 3 O 2 because it is the theoretical yield. If we put moles of NaHCO 3 in excess with vinegar (HC 2 H 3 O 2 ) and boil it, we would get grams of NaC 2 H 3 O 2 because it is the theoretical yield. If we put moles of NaHCO 3 in excess with vinegar (HC 2 H 3 O 2 ) and boil it, we would get grams of NaC 2 H 3 O 2 because it is the theoretical yield. Materials: 1 bottle of vinegar (HC2H3O2) 20 grams of Sodium Acetate (NaHCO3) 1 Bunsen Burner 1 Erlenmeyer Flask (200mL) 1 Tripod 1 Wired Mesh/Gauze Safety Goggles (according to number of group members) 1 Lighter

2 1 Spatula 1 Weighing Scale Procedure: 1. Gather all the materials needed. 2. Gather 4.5 grams of NaHCO 3, use weighing scale to measure 2.5 Preferably, place a piece of paper over the weighing scale for easy removal of NaHCO 3 3. Place the 4.5 grams of NaHCO 3,as a limiting reactant, into the Erlenmeyer Flask 3.5 Add vinegar in excess 4. Continue adding vinegar until reaction stops (stops bubbling) 5. Place the Erlenmeyer flask on the tripod (use wired mesh) 6. Place the Bunsen Burner under the tripod 7. Ignite the flames 8. Wait for liquid to evaporate 9. Once the liquid evaporates... 1.Weigh the flask 2. Subtract the weight with the weight of the empty flask 3. Compare the weight with the theoretical yield 10. Repeat for the other 2 different amounts of NaHCO 3 Raw Data Table Amount of NaHCO 3 Theoretical Yield Actual Amount moles (4.5 grams) 4.4 grams 4.5 grams moles (4.5 grams) 4.4 grams 5.1 grams moles (4.5 grams) 4.4 grams 4.7 grams Observations Quantitative Data Unknown amount of NaC 2 H 3 O 2 left the flask during the reaction Qualitative Data

3 The first trial s NaC 2 H 3 O 2 became quite brown in color The flasks were quite dirty (especially the first trial) Trials 2 and 3 were much more white in color Trial 1 used the bunsen burner to heat up while trail 2 and 3 uses the oven Results are unreliable because the data seems very wrong (more Actual Amount than 4.5 grams) Data Processing Converting Moles to Grams moles of NaHCO 3 Molar Mass of NaHCO 3 = * 84 = = 4.5 grams First I find the molar mass of the Baking Soda (84). Then multiply the molar mass with the amount of baking soda in moles. This would give us the amount of baking soda in grams. Lastly I rounded the number to get the final answer. (baking soda in moles) * (molar mass) = (baking soda in grams) Finding Theoretical Yield grams * 82 / * 82 / 84 = = 4.4 grams To find the theoretical yield we must first find the weight of baking soda in grams. After converting, we then multiply it with 82. Lastly we divide the number with the molar mass of baking soda which is 84. (baking soda in grams) * (82) / (molar mass) = (theoretical yield) Mean Average of Actual Amount / 3 = 4.76 grams Add all the results from all the three trials then divide the result with the number of trials (3). (trial 1 result) + (trial 2 result) + (trial 3 result) / (number of trial) Percent Error

4 Trial 1 : / 4.5 * 100 = 2.2% Trial 2 : / 5.1 * 100 = 13.7% Trial 3 : / 4.7 * 100 = 6.4% To find the percent error, we must find the theoretical yield and all the results. First we subtract the actual yield with the theoretical yield. After that, divide the number with the actual yield then finally multiply it by 100 to get the percentage. Once you get the percentage, you can subtract it with 100 to get the percent yield (theoretical yield) (actual yield) / (actual yield) * 100 = (percent error) 100 (percent error) = (percent yield) Processed Data Table Processed Data Table of Experimental Yield Sodium Acetate Limiting Reactant Baking Soda (g) Sodium Acetate Theoretical Yield (g) Sodium Acetate Actual Yield (g) Percent Yield (%) Conclusion In conclusion, the results that we have gathered are not reliable at all, making this experiment invalid. Even though the percent error is low, the number of Sodium Acetate produced is higher than the original amount of Baking Soda, which is impossible. When we look at the result of all the three trials, we can clearly see how the amount is more or the same. Trial 1 being 4.5g, trial 2 5.1g and trial 3 4.7g. This would of course be impossible if it weren t for the numbers of errors that were made during the experiment. One of the most important is the contamination. I feel that the main reason that our result are higher than the amount of baking soda is because of the contamination. Various other substances that are left in the flask mixed with the reaction increases the weight of the flask at the end. Because we have no way of separating the Sodium Acetate from the flask and the other substances in it, we cannot differentiate between the Sodium Acetate and other random

5 substances that are in the flasks. Evaluation Error Significant Solution Contamination. Dirty Erlenmeyer flasks causes the results to be highly inaccurate, adding other substance into the reaction. In Trial 1, the reaction caused some of the NaHCO 3 to come out of the flask. Clean the Erlenmeyer flasks before use. Handle the vinegar with more care. Estimate amount of NaHCO 3 loss and add it to the results. Trial 1 uses the Bunsen Burner while Trial 2 and 3 both uses only the oven. Trial 2 and 3 was left in the oven much longer than Trial 1 was. We did not use the same weighing scale for all trials. Medium Stick with one method throughout the whole experiment, no matter the time taken. Set a time for all the trials. Designate 1 weighing scale per group and do not change it. The experiment has far too many high significant errors for it to be reliable. We encountered several problems during the experiment (mainly the short amount of time we were given). The results are no where near correct, several unwanted variables affected the final result, mainly the changes in the procedure and the contamination of the Erlenmeyer Flasks. Also we had no way of accurately measuring the amount of Sodium Acetate in the flasks since it was impossible for us to remove it and separate from the rest of the substances that might be in the flask. Next Testable Question What is the difference of the two method of evaporation (bunsen burner and the oven) and

6 how will it impact the amount of Sodium Acetate?