Formal Lab Report Exp. 15 (Example) PDF

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Formal Lab Report for Gen Chem Lab II...

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CHEM 1225, Section 22

Experiment 15 Formal Lab Report

Evan Espinel & Samuel Philips

Introduction The Athenium Baking Soda Company uses a technique that combines brine and crystalline ammonium hydrogen carbonate to form NaHCO3. Due to the trace amounts of LiCl, CaCl2 and KCl in brine, there is a chance that these contaminants may be present in the baking soda. CaCl2 and LiCl are dangerous for human consumption and though KCl is only dangerous in large quantities it is necessary for its presence to be as limited as possible. If any of these contaminants are found in the test sample, then the company will have to rework their production method. This requires a quality control process to determine the percent composition of sodium bicarbonate and the identity of the impurities present within the sample if any. To figure out the amount of NaHCO3 as well as the presence and identity of any dangerous contaminants we are going to use emission analysis, titration and thermal gravimetric analysis. Titration is a technique used to determine the concentration of something in an unknown solution by analyzing specific volume of known concentration. We created our known solution using HCl to act as our known solution. We can then determine the concentration of NaHCO3 in our baking soda sample. When we reach an equivalence point, when the amount of HCl neutralizes the NaHCO3, the unknown solutions concentration can be determined. This will allow the percent by mass of baking soda to be found through the use of this equation: HCl (aq) + NaHCO3 (s) = NaCl (aq) +H2O (l) +CO2 (g) This will be done twice in order to increase the accuracy of our results. We will also be determining the percent by mass of the solid in a mixture using thermal gravimetric analysis. We will find the mass of the solid NaHCO3 in the mixture with distilled water. When heated in a crucible NaHCO3 goes through a decomposition reaction: 2 NaHCO3 (s) --> Na2CO3 (s) +H2O (g) + CO2 (g) When heated, CO2 and H2O are removed as gas particles. From the mass lost the percent by mass of NaHCO3 can be determined. Emission analysis allows us to determine potential contaminants in our sample. Group IA and Group IIA metals can be identified by the wavelength and intensity of the contaminant through the use of spectrophotometry. Metals release a distinct patter of emission wavelengths and by comparing that data with the data gathered from our sample we can determine the identity of the contaminant.

Experimental Chemicals: 

Sodium Bicarbonate (solid, primary standard base)



Baking Soda sample (mixture)



Approximately 1.0 M hydrochloric acid solution



pH 7.00 buffer solution



0.1 M Calcium Chloride solution



0.1 M Lithium Chloride solution



0.1 M Potassium Chloride solution

Procedure: Clean crucible with the 1.0 M hydrochloric acid solution. Determine the mass of just the crucible and crucible lid. Place approximately 1.0g of the baking soda sample in the crucible and determine the mass. Set up crucible with the clay triangle, and iron ring above the bunsen burner. Ignite the burner and heat gently for 5 minutes. Place the crucible lid on top of the crucible so that a small gap is left for gases to escape. Do not let the substance melt, if it begins to lower the heat. Then adjust the flame until the flames shape a blue cone below the crucible and heat vigorously for 15 minutes. Again, place the crucible lid as previously instructed and do not let the sample melt. Remove the crucible from the flames and let it cool until at room temperature. Determine the mass of the crucible, lid, and remaining sample. Dispose of the sample and clean the crucible with the 1.0 M hydrochloric acid solution. Repeat the steps above with a second 1g sample. Record the changes in mass, use them and the stoichiometric equation for the decomposition of sodium bicarbonate to determine the percent mass of sodium bicarbonate in the baking soda. Use this stoichiometric equation to derive the percent mass: 2 NaHCO3 -> Na2CO3 + H2O + CO2. If the thermal gravimetric analysis does results do not show 100% sodium bicarbonate composition, analyze the emission spectra of the possible contaminants. Place each substance (the three contaminants, pure sodium bicarbonate, and the sample) each in a separate cuvette. For the pure sodium bicarbonate, dilute to 1 M solution with water and then place in cuvette. Test the emission spectra of each substance using the emission spectrometer and the MeasureNet System. Compare the � value for the highest intensity emission for each substance

to the maximum � value for the highest intensity emissions of the baking soda sample. Determine what impurities are present in the sample. Now titration is required to figure out the HCL concentration. An average amount of HCl should be calculated in order to standardize the results. In this experiment we calculated our average moles of HCl used as 0.00927mol HCl. We placed our buret above drop counter and began to release the HCl solution into the sodium carbonate solution. The pH and mL of HCl needed to reach equivalence point are recorded for every trial. The data gathered is then used to determine the concentration of HCl given the ratio of sodium carbonate in mystery sample to HCl in the chemical reaction.

Results Titration: Trial #1

7.69 mL*(1L/1000mL) * (1 mol/L) =

0.00769 mol HCl

Trial #2

10.846 mL*(1L/1000mL) * (1 mol/L) =

0.01085 mol HCl

Avg. Moles

(0.01085+0.00769)/2 =

0.00927 mol HCl

Trial #1 Equivalence Point

7.69 mL

Trial #2 Equivalence Point

10.846 mL

Moles of NaHCO3 Mass Fraction of by NaHCO3 titration Avg. Percent by Mass

0.00927 mol HCl *(1 mol NaHCO3 /1 mol HCl) = 0.779 g NaHCO3 /2.00 g unkown =

0.00927 mol NaHCO3 or 0.779 g NaHCO3 0.39

(0.39 [Titration] +0.449 [Thermal Grav.])/2 =

0.419 = 42% NaHCO3

Table 1: Trial #1 Titration of baking soda solution with 1.0M HCl Table 2: Trial #1 Titration of baking soda solution with 1.0M HCl

Table 2: Trial #2 Titration of baking soda solution with 1.0M HCl

Table 3: Emission Spectroscopy of KCl

Table 3: Emission Spectroscopy of CaCl

Table 4: Emission Spectroscopy of LiCl

Table 5: Emission Spectroscopy of Unknown

Calcium Chloride

Lithium Chloride

Potassium Chloride

Sample

623.75nm & 553.84nm

670.14nm

765.78nm & 589.37nm

765.78nm & 588.61

Table 6: The Baking soda sample contained Potassium Chloride, as both the sample and potassium chloride solution have maximums at 765.78nm and about 589nm.

Thermal Gravimetric Analysis: 1.000g NaHCO3*(1 mol NaHCO3/84.01 g NaHCO3) * (1 mol CO2/2 mol NaHCO3) * (44g CO2/1mol CO2) =.262g CO2 liberated for every g NaHCO3

1.000g NaHCO3*(1 mol NaHCO3/84.01 g NaHCO3) * (1 mol H2O/2 mol NaHCO3) * (18.02 H2O/1mol H2O) =0.107g H2O liberated for every g NaHCO3 Trial 1: Mass change of sample: 1.020g-0.884g=0.136g of CO2 and H2O liberated 0.136g CO2 and H2O*(1.000g NaHCO3/0.369 g CO2 and H2O) =0.368g NaHCO3 in the sample 0.368g NaHCO3/1.020g sample=36.1% NaHCO3 Trial 2: Mass change of sample: 1.028g-0.827g=0.201g of CO2 and H2O liberated 0.201g CO2 and H2O*(1.000g NaHCO3/0.369 g CO2 and H2O) =0.545g NaHCO3 in the sample 0.545g NaHCO3/1.028g sample=53% NaHCO3 Average: (36.1%+53%)/2=45% NaHCO3

Discussion For titration, the purity of baking soda for Trial #1 is 42% of NaHCO3 in the sample. This indicates that the sample is quite impure, because the other 58% are impurities. This is consistent with the thermal gravimetric analysis data which suggests that there is a lesser chance of human error however, it is still possible. The determined purity of sodium bicarbonate after the gravimetric analysis was 36.1% for Trial #1 and 53% for Trial #2 for an average of 44.5%. It can be determined by this data and the data gathered from the titration that this sample is impure due to the impurities being approximately 54.5% of the sample. For the emission spectroscopy, we compared the baking soda sample to potassium chloride, Lithium chloride and calcium chloride and after the data was gathered, we determined that our sample most likely contains potassium chloride. We made this observation by analyzing the maximum intensity wavelengths for each spectrograph and because both potassium chloride

and our sample had maximums at around 765.78nm and 589nm we were able to make this assumption with great confidence.

Conclusion We conducted this experiment in an effort to determine the purity of the baking soda produced by the Athenium Baking Soda Company in order to assure its safety for human consumption. After our quality control experiment was completed and we had analyzed the data from the three different techniques gathering information, we confidently determined that the sample is 42% sodium bicarbonate. The other 58% was potassium chloride. This data and findings can be utilized by the Athenium Baking Soda Company in order to improve their production and refinement process....