Identification and Synthesis of Unknown Compound 829p By Tyler Blevins Group members: John Creps, Ashley Gergen, Alison Werneiwski
Abstract: An unlabeled container of a white compound was discovered in the chemistry stockroom. In order to dispose of the substance safely, the identity as well as the chemical and physical properties of the compound needs to be identified. The identity of the unknown white compound (UWC) has been narrowed down to a list of 15 different compounds. There was 5 grams of the UWC that was available for testing. Various tests, such as solubility test, conductivity test, pH test, ion test, and flame test, were used to determine the properties of the unknown compound. The results from the tests were used to compare the properties of the UWC to the properties of the possible compounds for identification purposes. The tests indicated that compound 829p is potassium sulfate. Once the identity of the UWC was discovered, the compound was synthesized and tested to compare its properties to those of the UWC in order to verify that they are the same compounds. Potassium sulfate was successfully synthesized and the testing confirmed that its properties were an exact match to those of 829p.
Introduction: During an inventory check of the chemistry stockroom, an unlabeled container was discovered and its contents were unknown. In order to properly dispose of the unknown compound, its identity and chemical and physical properties needed to be investigated. Proper disposal of compounds is very important because they can potentially have harmful effects on their surroundings. Not all compounds are safe to pour down the sink because it’s possible that they could react with other compounds and produce toxic gases and byproducts. Therefore, identifying unknown chemical substances and properly disposing of them is an extremely
important branch of science. Using a wide variety of tests to identify an unknown substance can show if the substance is toxic, dangerous, highly reactive, difficult or easy to dispose of and many other useful properties the substance possesses. In everyday life, this practice can be helpful in cleaning chemical spills, identifying compounds such as the salt that forms in a pan when water is boiled, preventing corrosion in pipes, and creating fragrances. This practice has even been used to identify a compound that mimics one of the brains growth factors that protects brain cells from damage. In this lab, 5 grams of an unknown white compound was discovered and its identity was narrowed down to a list of 15 compounds, all of which look similar. The 15 compounds include CaCO3, MgSO4, NaC2H3O2, CaCl2, KCl, Na2CO3, Ca(NO3)2, KNO3, NaCl, MgCl2, Na2SO4, NH4Cl, K2SO4, (NH4)2SO4, and K2CO3. Because they look similar, stating a hypothesis is difficult. In the remainder of this report, the process and results for the identification and synthesis of the unknown white compound are explained in detail.
Experimental and Results: The experiment to identify and synthesize the unknown compound was broken up into three days. On the first day of the experiment, multiple tests were performed. Our group decided that we would first try to narrow down which of the suspected compounds matched the unknown compound by comparing their physical traits. We noted that our unknown compound had a texture that was more similar to that of sugar as opposed to powder like many of the compounds. The 15 possible compounds were analyzed and the texture of the unknown compound matched the texture of 3 of them. The compounds that matched the texture of the UWC were Na2SO4, K2SO4, and NaCl. For the remainder of day one, the three suspected compounds and the UWC were tested in various ways, the first of which was the solubility test. For the solubility test, four 50 mL beakers were filled with 25 mL of deionized water and a small
amount of 829p, Na2SO4, K2SO4, and NaCl was placed in its respective beaker. The compound and water in the beakers were stirred using a stirring rod and the solubility of the mixture was recorded. All four of the mixtures were soluble, so the list was not narrowed down from the solubility test. Directly following the solubility test, the conductivity test was performed. Using four clean beakers, 100 mL of deionized water was poured into each one. Next, a digital scale was used to measure out .75g of each of the four compounds and they were each placed in their own beaker. A stirring rod was used to create an aqueous solution in each of the beakers. Using a conductivity probe that was hooked up to a computer that was running a program called LoggerPro, the conductivity of each of the aqueous solutions was recorded. The results are as follows:
Conductivity(µS/cm)
Na2SO4
K2SO4
NaCl
829p
3326.0
3324.8
3328.1
3325.5
As the results show, the conductivity of each of the four aqueous solutions is very similar and the test did not help narrow down a possible match for the UWC. The next test that was performed was the pH test. The same beakers containing the aqueous solutions used in the conductivity test were used for the pH test as well. The only difference between the two tests was that in the pH test, a pH probe was connected to the LoggerPro system instead of a conductivity probe. The probe was placed in each of the solutions and the pH was recorded. The results were:
pH
Na2SO4
K2SO4
NaCl
829p
5.65
5.75
5.69
5.65
The results of the pH test showed that each of the aqueous solutions was very similar and they are all fairly neutral. Because the results were so close, we were not able to narrow down the list of possible matches to the UWC any further. The next test that was performed was the ion test. Sulfate ions were tested for first. In order to set up the experiment, a test tube rack and one test tube were retrieved from the lab and set up on the table. The components that were added to the test tube were 1.0 mL of 6M HCl and 1.0 mL of BaCl2. The next component that was added to the test tube was 1.0 mL of the unknown solution. Upon mixing the solution, a white precipitate formed which indicated that the compound 829p contained a sulfate ion. The results for the ion test for sulfates allowed the list of possible compounds that matched the UWC to be narrowed down to MgSO4, Na2SO4, K2SO4, and (NH4)2SO4 although it was suspected that the compound 829p was either Na2SO4 or K2SO4. On day 2 of the UWC experiment, the ion test for sulfates was performed once again in order to double check that the compound 829p contained sulfate ions. The experiment was performed under the same conditions and in the same manner as described in the previous paragraph and the results were the same which meant that the UWC contained a sulfate ion. The flame test was the next test to be performed. In order to perform the flame test, a Bunsen burner and nichrome wire were needed. The Bunsen burner was connected to the gas valve using a rubber hose and it was then lit and adjusted to have a steady flame. In order to make sure that the nichrome wire was clean before each compound was tested, a test tube of HCl and a test tube of deionized water were also required. The flame test is performed by dipping the nichrome wire into the HCl first, and then into the water in order to make sure the results are solely from the compound being tested. The clean wire is then dipped into the compound being tested and then
held over the flame. Using previous knowledge, we compared the color of the flame from all of the sulfates to the color of the flame from the 829p compound. The results are as follows.
Color
(NH4)2SO4
Na2SO4
K2SO4
MgSO4
829p
No Reaction
Bright Yellow
Purple/Orange
Orange
Purple/Orange
The flame test turned out to be a very significant test because the only compound whose color matched that of the UWC even remotely was K2SO4 and therefore it was concluded that the compound 829p was, in fact, comprised of potassium sulfate. The third day of lab was devoted to synthesizing the compound K2SO4. The balanced chemical equation for synthesizing it was 2KOH (aq) + H2SO4 (aq) => K2SO4 (s) + 2H2O (g). Once the proper equation was figured out, the amount of each reactant needed was calculated. The calculations are shown below:
x
x
x
x
x
=
x
=
The first step taken in the synthesizing process was to get a 500mL beaker and retrieve a bottle of KOH and a bottle of H2SO4 from the lab. The reactants were measured out to the values calculated above in a graduated cylinder and then they were both poured in to the beaker. The pH of the solution was tested using pH probe and it was 1.76 which is very acidic. In order to neutralize the solution, KOH was continually added with a pipet until the solution reached a neutral pH of 6.74. By the time the solution was neutralized, a solid had formed at the bottom of the beaker. A hot plate was heated up and the beaker was then placed on it in order to boil off the
H2O. When the majority of the water had boiled off and all that was left was the solid K2SO4, the 500mL beaker was placing in the oven for 30 minutes in order the vaporize all of the water molecules off so that pure K2SO4 was the only product that was left in the beaker. Using a digital scale the beaker was measured and then the K2SO4 was scraped out into a test tube. The empty beaker was then weighed again and the mass was subtracted from the first value in order to give the mass of the K2SO4 synthesized. The chemical reaction created 5.814 grams of K2SO4. The goal for the synthesis of the compound was to make 1gram of product, but because 6M reactants were used instead of 1M reactants, the expected mass of the product was 6 grams. The percent yield of the reaction was then calculated by dividing 5.184 by 6 and multiplying the resulting number by 100. This equation stated that the percent yield of the reaction was 96.9%. The K2SO4 synthesized in the reaction was then tested in order to make sure that the test results matched the results of the 829p compound. The solubility test and the flame test were performed in the same way they were in day 1 and 2. The results of the tests confirmed that the compound created matched 829p perfectly.
Discussion: The interpretation of the data was mostly done in the previous section. The chemical and physical properties of the tested compounds have been explained in detail, the results of the tests and processes taken to find the results have also all been analyzed, and the compound was identified and synthesized. The compound 829p can now be properly disposed of using the information gathered during the experiments. One of the main limitations of the data imposed by the lab was that the only available cation test performed was the flame test. The flame test could potentially have been contaminated by using the same nichrome wire over and over for different compounds. Although it was cleaned in between each compound, it is possible that some
compounds could have carried over and affected the results of the compounds tested afterwards. There was a relatively small amount of errors that could have affected the results of this lab. The percent yield of the synthesized compound was very high and it may have been even higher had we gotten absolutely all of the K2SO4 out of the beaker before weighing the results. The majority of it was definitely retrieved, but it is possible that some was left over in the beaker. Another source of error was that KOH had to be added to the solution during synthesis in order to raise the pH level. This means that there was a limiting reactant in the reaction and there was some KOH left over with the water in the beaker once the solid was formed. This most likely did not affect the results very much because only the solid was weighed out and the KOH would have been in liquid form.
Conclusion: The unknown compound underwent various tests and through analysis of the results of the tests, it was confirmed that compound 829p is K2SO4. During the first part of the experiment, the unknown compound was narrowed down to 4 compounds, all of which were sulfates, but it was suspected to be either potassium sulfate or sodium sulfate. Upon further tests and analysis of the four sulfate compounds, the identity of the unknown white compound was discovered to be potassium sulfate. Many of the chemical and physical properties of the unknown compound were discovered and recorded. Once the identity of the compound was discovered, 5.814 grams of it was synthesized with a 96.9% yield. Overall, this lab was very successful.
References: (1) “Flame Colors as Chemical Indicators.” Flame Colors. N.p., n.d. Web. http://hyperphysics.phy-astr.gsu.edu/hbase/Chemical/flame.html (accessed March 10, 2013)
(2) “Flame Test.” The Columbia Encyclopedia, 6th ed. 2012. Encyclopedia.com. . (accessed March 10, 2013)
(3) “Identification of an Unknown Substance.” CSU Stanislaus Science Web. http://science.csustan.edu/byrd/chem1002/unknown.htm (accessed March 10, 2013)
