Identification of the Unknown White Compound by Compound Synthesis and Tests of their Physical and Chemical Properties

Identification of the Unknown White Compound by Compound Synthesis and Tests of their Physical and Chemical Properties Due March 13th, Spring 2019 Abstract ! An unlabeled container with 2 grams of a white compound has been discovered in the chemistry stockroom. It is imperative that the compound should be identified for its correct disposal. After reviewing the stockroom inventory list, the Unknown White Compound was narrowed down to 15 compounds. Two sets of tests were conducted to identify the physical and chemical properties of the UWC. The initial tests consisted of a flame test, ion tests, and pH paper test, which yielded sufficient data to speculate the identity of the UWC to be potassium sulfate. Based on the initial findings, it was hypothesized that the UWC is potassium sulfate if the stockroom potassium sulfate and the synthesized potassium sulfate yielded the same physical and chemical properties when tested. The violet flame, the precipitation of barium sulfate, and the same range of pH paper test for both the UWC and the synthesized potassium sulfate confirmed the identity of the UWC to be potassium sulfate. Conductivity test for stock potassium sulfate and the UWC yielded the same confirmatory results of 252.6 µS/cm. Introduction! Labeling is a common practice not only in the world of science but also in our daily lives. The importance of correct labeling cannot be emphasized enough. Simply from keeping our belongings organized at home to making sure the safety of medication therapies, we live in an era where labels are a crucial part of our lives. It is not difficult for an emergency medicine physician to see a patient who took an unknown medicine due to label related issues, and the identity of the unknown item can easily cost a life if unidentified.1 That is why Food, Drug, and Cosmetic Act of 1938 clearly defined the adulteration and misbranding of drugs and food products.2 The same is applied in the chemistry lab. Chemistry labs are stocked with a number of chemical compounds that could potentially pose a great threat to the personnel working in labs. Therefore, it is crucial to keep quality labeling standards in chemistry labs.4 ! Scientific research on the identification of an unknown organic compound published in the Journal of Chemical Education indicates the importance of the identification of unknown compounds. The organic chemistry lab exercise was used to introduce the students to organic spectroscopic techniques, such as Mass spectrometry, IR, HNMR, and CNMR, and to learn the usefulness and the limitations of each technique. This is a great opportunity to have hands-on real-life experiences operating the instrumentation.3##The spectroscopic techniques are essential to more accurate experiments. In this report, a flame test was used as a quick and easy method for the identification of the cation content in the UWC; however, a spectroscopic technique can be further implemented in order to yield more accurate results.! In this report, 2 grams of an unknown white compound was tested. The objective was to identify the UWC so that the compound could be disposed of properly. In accordance with the list of compounds available for the lab, the identity of the UWC was narrowed down to one of the following 15 compounds listed below(Table 1.). ! Table 1. List of possible identities of the UWC ions Ca2+ K+ Mg2+ Na+ NH4+ - - - NaC2H3O2 - CaCl2 KCl - NaCl NH4Cl K2CO3 - Na2CO3 - C2 H3 O 2 ClCO3 2- CaCO3 NO3 - Ca(NO3)2 KNO3 MgCl2 - - SO4 2- - K2SO4 MgSO4 Na2SO4 (NH4)2SO4 In order to identify the UWC, a variety of tests were carried out to find out its physical and chemical properties. The initial set of tests was to determine the identity of the compound, and the second set of tests was to confirm the findings of the initial tests. The initial tests consisted of a flame test, ion tests, and pH paper strip test. Ion tests included precipitation reactions with silver nitrate and barium chloride solutions, ammonia smell test by adding sodium hydroxide to the UWC solution, and carbonate ion test by adding a few drops of hydrochloric acid.! Followed by the initial tests, it was hypothesized that the identity of the UWC should be potassium sulfate if the stock potassium sulfate and the synthesized potassium sulfate yielded the same test results as the UWC. Once reasonable speculation of the identity of the UWC was established, potassium hydroxide and sulfuric acid were mixed to synthesize the identified white compound. The correct identification of the UWC was critical before the synthesis of the compound as it could potentially pose serious harm. The confirmatory experiment consisted of a flame test, ion test and the pH test of the synthesized compound, and the conductivity test of the UWC and the stockroom potassium sulfate. The test results were compared to confirm the identity of the UWC. Based on the findings, the identity of the UWC was confirmed, and the proper disposal was suggested based on the material safety data sheet. Experimental ! A Flame test was carried out to identify the cation present in the UWC. 10 mL of 6M HCl solution, 10 mL of deionized water, and 250 mg of the UWC dissolved in 10 mL of deionized water were prepared in each 100 mL beaker. Nichrome wire was dipped into the HCl solution, rinsed with water and then heated in the flame to clean the possible contamination prior to the flame test. Once the wire cooled down, it was dipped into the UWC solution and placed into the flame to observe the flame color.#! # Two sets of precipitation test were carried out. Firstly, 1 mL of 6M HNO3 solution and 1 mL of 0.1M AgNO3 solution were added to the test tube containing 1 mL of the UWC solution. Then, 1 mL of 6M HCl and 1 mL of 0.1M BaCl2 were added to another test tube containing 1 mL of the UWC solution. Observations were made each time to see if there was any precipitation.! Ammonium ion test was carried out by adding 1 mL of 6M NaOH to 1 mL of the UWC solution. Once the solutions were completed mixed, observations were made by checking for a distinct smell above the solution and holding a damp red pH paper above the solution.! Carbonate ion test was carried out by adding a few drops of 6M HCl to 1 mL of the UWC solution. During the reaction, observations were made to see if fizzing or effervescence occurred.! pH test was carried out using pH paper strips. A pH strip was dipped into the UWC solution and the color was compared to the pH color chart to determine its value.! Once the identity of the UWC was determined, the known compound(K2SO4) was synthesized using a balanced chemical equation. 11.50 mL of 1M KOH and 5.75 mL of 1M H2SO4 were mixed in a beaker to make 17.25 mL of 0.33M K2SO4 solution. A pH paper strip was used to make sure that the neutralization reaction above was completed. The final solution was placed on a hot plate to evaporate the water and to form approximately 1 gram of potassium sulfate. With the synthesized compound, confirmatory flame test, ion tests, and pH test were carried out following the same steps used for the identification of the UWC. The test results were compared to that of the UWC.! Confirmatory conductivity test was carried out for stockroom potassium sulfate and the UWC using a conductivity probe(Vernier, CON-BTA, ±3% accuracy of full-scale reading for 0 to 2000 µS/cm range) and Logger Pro¨ software. To prepare 10 %w/w K2SO4 solution, 250 mg of stock K2SO4 was added to 2500 mg of deionized water. The conductivity probe was dipped into the completely dissolved solution to measure the conductivity. By adding a proportionate amount of water described in Table 7., the 10% solution was diluted to 5%, 2%, and 1% to measure the changes in conductivity. To prepare 10%w/w the UWC solution, 500 mg of the UWC was added to 5000 mg of deionized water. The conductivity probe was dipped into the completely dissolved solution to measure the conductivity. The 10% solution was diluted to 5%, 2%, and 1% to measure the changes in conductivity. Results ! Table 2. below shows the collective data acquired from the tests carried out to identify the physical and chemical properties of the UWC and the synthesized potassium sulfate. ! Table 2. The UWC & Synthesized K2SO4 Test Results Tests UWC results Synthesized K2SO4 Flame Test pale violet pale violet halide ion test no precipitate no precipitate sulfate test cloudy precipitate cloudy precipitate ammonia test negative negative reaction with HCl negative negative pH test neutral or slightly acidic neutral or slightly acidic The flame test result for the UWC solution yielded pale violet flame. The precipitation test carried out with silver nitrate showed no precipitate. The precipitation test carried out with barium chloride showed cloudy precipitate. The Ammonia test yielded neither the distinct ammonia smell nor the changes in color of the pH paper strip. The reaction with hydrochloric acid showed no fizzing or effervescence. The pH test of the UWC solution turned out to be slightly acidic. The confirmatory test results of the synthesized compound(K2SO4) showed the same results as that of the UWC as shown in Table 2. ! In addition, the confirmatory conductivity test yielded almost identical values for both stock potassium sulfate and the UWC solution as shown in Table 3. The conductivity for the stock potassium sulfate solution averaged to 252.5 µS/cm, and the conductivity for the UWC solution averaged to 252.7 µS/cm.! Table 3. Conductivity Test Data Stock K2SO4(g) water(g) solution(g) concentration(%w/w) conductivity(µS/cm) 0.250 2.258 2.508 9.968 252.5 0.250 4.828 5.078 4.923 252.4 0.250 11.779 12.029 2.078 252.7 0.250 24.767 25.016 0.999 252.4 UWC(g) water(g) solution(g) concentration(%w/w) conductivity(µS/cm) 0.504 4.515 5.019 10.042 252.5 0.504 9.534 10.038 5.021 252.7 0.504 24.557 25.061 2.011 252.9 0.504 49.532 50.036 1.007 252.7 Discussion Each cation is known to yield distinct flame colors(Table 4.). The flame test results for the UWC and the synthesized potassium sulfate both yielded pale violet color to indicate the Table 4. Cation Flame Colors Cation Ca2+ K+ Mg2+ Na+ NH4+ Flame Color orange pale violet white yellow colorless potassium content in the UWC. The flame test is a simple procedure used to identify elements in ionic compounds based on the characteristic emission spectrum of each element in the absence of precise analysis of a compoundÕs spectrum. The test is performed by placing a crystal of an ionic compound or a drop of its solution into a flame, each metal exhibits characteristic colors in flame tests. When an atom absorbs energy, an electron in a lower energy orbital is excited or promoted to a higher energy orbital. However, the atom is unstable, and the electron quickly falls back or relaxes to a lower energy orbital. As it does so, it releases a photon of light containing an amount of energy precisely equal to the energy difference between the two energy levels with the characteristic emission spectrum.5 For potassium, pale violet color can be observed as it was for the UWC and the synthesized potassium sulfate. ! Four types of ion tests were carried out to identify the presence of chloride ion, sulfate ion, ammonium ion, and carbonate ion. The ion test results showed that the UWC contained sulfate anion. It was identified by the precipitation reaction between barium chloride solution and the UWC solution. Whether precipitation forms or not is dependent on the solubility of the products when two different solutions are mixed together. The solubility guideline(Table 5.) was used to determine and analyze the results, and the expected reactions are listed on Table 6. ! Table 5. Solubility Guidelines A cloudy precipitate was formed when the barium chloride solution and hydrochloric acid were added to the UWC solution. This confirmed the present of sulfate ion in the UWC solution.! Other than the two tests, the halide ion test showed no precipitate to confirm the absence of chloride ion in the UWC solution, the carbonate test showed no presence of carbonate ion, and the ammonium test showed no presence of ammonium ion. ! Table 6. Ion Test Reactions Reactant Chemical Equations BaCl2(aq) BaCl2(aq) + XSO4(aq) → BaSO4(s) + XCl2(aq)! BaCl2(aq) + K2CO3(aq) → BaCO3(s) + 2KCl(aq) AgNO3(aq) AgNO3(aq) + XCl(aq) → AgCl(s) + XNO3(aq) HCl(aq) 2HCl(aq) + X2CO3(aq) → 2XCl(aq) + CO2(g) +H2O(l) NaOH(aq) NH4+(aq) + OH-(aq) → NH3(g) + H2O(l) Should the UWC solution contain carbonate ions, it will show fizzling or bubbling when hydrochloric acid is added to the solution. This is because carbon dioxide gas is produced when metal carbonate compounds react with acids. We can easily observe the same reaction when we burp after taking a tablet of common over-the-counter antacid, such as TUMS that contains calcium carbonate(CaCO3). ! As the chemical equation(Table 6.) demonstrates, the ammonium ion test is also a gas evolution reaction where ammonia gas is produced when two compounds are mixed. Should the UWC contain ammonium ions when mixed with sodium hydroxide, it will yield ammonia gas and water. The ammonia gas is a weak base; therefore, it turns the damp red pH paper to blue when held above the solution. The pH paper was held above the solution instead of dipping into the solution. This is because the mixed solution may still contain the basic sodium hydroxide solution which could also turn the red pH paper to blue.! Based on the test results and its comparison to the list of possible identity of the UWC, it was evident that the UWC was potassium sulfate. The pH test turned out to be slightly acidic or neutral as opposed to the expected value of slightly basic or neutral; however, considering the uncertainty of pH paper strips and the close range to the theoretical pH of potassium sulfate solution, it was reasonable to speculate that the identity of the UWC was still potassium sulfate.! To confirm that the UWC was potassium sulfate, the compound was synthesized to go through the same set of tests as the UWC. Potassium Sulfate was synthesized using the balanced chemical Equation (1). 2KOH(aq) + H2SO4(aq) → K2SO4(aq) + 2H2O(l) Equation (1) Where 2 moles of potassium hydroxide and 1 mole of sulfuric acid produce 1 mole of potassium sulfate and 2 moles of water. Furthermore, The volume of each reactants of known concentration can be calculated using Equation 2. moles of solute = M(molarity) x V(liters solution) Equation (2) In this lab report, 11.50 mL of 1M KOH and 5.75 mL of 1M H2SO4 were mixed to make 17.25 mL of 0.33M K2SO4 solution. That is, The reaction between 11.5E-03 moles of KOH and 5.75E-03 moles of H2SO4 produced 5.75E-03 moles of K2SO4 and 11.5E-03 moles of H2O. Therefore, evaporating the water from the product yields 5.75E-03 moles of K2SO4, which is approximately 1.00 gram of K2SO4.! Despite the careful measurements and the above calculation, a few more drops of potassium hydroxide had to be added to reach a neutral state either because the sulfuric acid solution was slightly more acidic or the potassium hydroxide solution was slightly less basic than the known concentration. ! The flame test, ion tests, and the pH test for the synthesized potassium sulfate yielded the same results as the UWC to confirm its identity.! When ionic compounds dissolve in water, the elements that consist of the compound become charged ions. The charged ions can also move freely in the solution and effectively carry a current. The value of conductivity depends on the concentration of ions, hence, the higher the concentration of ions, the greater the conductivity. Therefore, if the UWC and the stockroom potassium sulfate yield the same level of conductivity, it is reasonable to speculate that the two compounds consist of the same elements. Given that, the confirmatory conductivity tests of the UWC and the stockroom potassium sulfate were carried out and yielded the same results to verify that the hypothesis was correct.! It is to be noted that there were three main possible sources of error in the experiment. The first is the measurement of the color of the flame. It was clear that the flame was violet or purple; however, as it was a qualitative measurement using our own vision, this part of the test can be improved by utilizing a spectroscopic technique to analyze the exact wavelength of the emission. The second is the pH paper strip test. The pH paper test is a quick and easy method to identify if a solution is acidic, neutral, or basic; however, the data collected have limitations because they are qualitative and relative data. That is, the changes in the color of the strips can be analyzed differently by each person. To improve this part of the test, a pH probe can use used to measure the precise concentration of the hydronium ion present in the solution. The last to discuss is the conductivity measurement. In this lab report, despite the changes in the concentration of the ionic compound solutions, the conductivity value yielded the same values. This can be the issue of calibration or the concentration calculation error. pH probe calibration with an identified compound solution prior to the measurement will be able to resolve this uncertainty for future replication. The solution can also be slightly heated to expedite the dissolution, or it can be stirred for a longer period of time to make sure its complete dissolution. Conclusion! The purpose of the experiment was to identify as many physical and chemical properties of the UWC as possible to confirm its identity. Based on the initial test results, it was hypothesized that the UWC should be potassium sulfate if the stock potassium sulfate and the synthesized potassium sulfate showed the same test results. After the confirmatory ion test and flame test, it was reasonable to believe that the identity of the UWC was K2SO4. In addition, confirmatory conductivity also yielded the results to confirm that the hypothesis was correct.! For future replication of this experiment, the spectroscopy technique and the pH probe can be utilized to eliminate the sources of errors discussed above. The UWC identified in this report contained potassium which yielded a clearly different color than the other elements. However, if it was calcium and sodium that was to be differentiated, it would be difficult for plain eyesight to tell the difference. The utilization of spectroscopy should be able to resolve this issue as the technique can capture the exact wavelength of each light emission. The pH paper test used in this report is a qualitative data collection method; therefore, a pH probe can be used to collect quantitative data to solidify the findings. It is also important to be noted that time management is crucial in lab experiments. In that, teamwork, prior knowledge, and preparation are essential for the success of the lab. In line with that, as the conductivity probe and the logger pro computer software was all greek to group members, it might help expedite the learning process if the future lab sessions can include detailed instructions on such devices.! The findings and the procedures in this lab report have a significant meaning not only in the field of academic science but also in the field of everyday healthcare. For professionals working in pathology, toxicology and emergency medicine, the identification of an unknown substance is crucial to the treatment of a patient. In this lab report, the procedures did not utilize much of high-end techniques or instrumentation; however, it was enough to shed light on the importance of such processes and the limitations.