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Using Basic Lab Techniques to Identify Inorganic Contaminants Michael Pool CHM2045L.912 Yiming Li March 9th 2017 Introduction Determining a chemical substance can be extremely important when given an unknown.
Chemicals have many qualities that are unique, often times only sharing that quality with a handful of other substances. Identifying these qualities through reactions allows us to narrow down what our unknown could possibly be. Reactivity is simply a chemicals reaction to other chemicals or extremes. Using reactivity we can find out more about the substance and make decisions based on what is in front of us. For example, many chemicals have obvious reactions to open flame. Depending on a chemicals reaction to the extreme heat of a flame, we can often times narrow our unknown to a specific group of chemicals. According to EAG Labs, there are a few basic questions we can run thr ough before we begin any tests on our chemical to possibly assist in identifying our unknown. Is there expected to be a large amount of contaminate? What are the physical attributes of the substance? Any color, odor, or residues? Once we made these inferen ces we began testing our substance, narrowing down the possibilities and continued to test within our new parameters. Following the tests in this lab should provide the name of the chemical that begins as an unknown, within a reasonable margin of error. Methods In this experiment we were given an unknown inorganic contaminant and told to identify it. Using qualitative and quantitative tests, we found the identity of our unknown. Part 1 In the first week of the experiment we started with qualitative test s; flame, solubility, conductivity, and PH. To begin with, we did the flame test. We took a small sample of our given unknown and exposed it to an open flame. We recorded this result and repeated the test two additional times, receiving the same result. Ou r next test was conductivity, we place the instrument in a beaker with a solution containing 1% of our unknown and remainder water. Our third test was PH, we placed the solution in a beaker with some basic PH indicator strips, matching their color to the c hart. Our final test of week one was solubility, we decided to do this test last because after this test our solution is contaminated and not useful for any further tests. We tested the solubility of our unknown with Barium Nitrate, Sodium Hydroxide, and S ilver Nitrate. Taking the solubility tray and adding both substances in separate sections, and recording the results. We completed three trials of each of these tests to be sure that no mistakes were made. Part 2 In the second week of the experiment we h ad quite a bit of data on our unknown and had the option of performing two different types of tests, based on our assumption of what our salt could be. The two possible tests are both quantitative, meaning they are measured by the quantity rather than qual ities of the substance. The first option was gravimetric, which is suitable for unknowns that produce precipitates. You begin with filtering out the precipitate and air drying the substance. The weight of this filtered out material is compared with the exp ected weight of the reactant formed by your assumed substance. The second option is volumetric, which is suitable for subatances with acidic or basic properties. Depending on what you assume your substance to be, you react it with another substance similar to the titration mini -lab completed earlier in the semester, finding the titration point. Based on our initial results we decided to run the volumetric test. We pulled a burette with a stopcock from the stock room and set up our substances and adding the indicator to begin mixing them one milileter at a time, recording the PH between each addition. Once we reached the titration point, we recorded the amount added and continued, recording PH as we went on. Once we were completed with this we cleaned our la b area and analysed our data as a group. Safety Before, after, and during our experiment we were sure to follow all laboratory safety expectations. We entered the lab wearing all of the appropriate personal protective equipment, keeping our goggles on any time chemicals were being used by any group. The chemicals that required use of the hood were handled extremely carefully, watching to make sure there wasn’t any chance of inhalation. Luckily there were not any spills during our experiment, but if such a situation were to arise we would have been prepared. Our TA supervised the use of the burner when we performed the flame test. Results Below are the results from both weeks of the experiments. Week 1 Conductivity Flame Test PH Level Trial 1 55.6 Yellow 10 Trial 2 63.0 Yellow 10 Trial 3 59.2 Yellow 10 Table 1.1 Solubility Substance Reaction Barium Nitrate Brown, Didn’t dissolve Sodium Hydroxide Clear, Dissolved Silver Nitrate Brown, Didn’t dissolve Table 1.2 Table 1.1 Includes the first three tests we performed on our unknown; conductivity, flame test, and PH levels. Table 1.2 includes all the information and results of the solubility test we performed on the salt. Incase the table is not clear enough, when re acted with Barium nitrate we ended up with a brown mixture that was not completely dissolved. Next, the Sodium Hydroxide produced a clear, completely dissolved mixture.
Finally, the Silver Nitrate provided us with a similar result to the Barium Nitrate. Th e Flame test produced a yellow color in all three trials. Our readout for conductivity was 55.6, 63.0 and 59.2. All of these allowed us to make inferences on our unknown and come up with an assumption on what it could possibly be and gave us a starting poi nt for week 2, where we decided to perform the volumetric test. Below are the results of that test. The indicated PH is given on the Y -axis of the chart with the number of ML of reactant added given on the X -axis. Week 2 Graph 2.1 Discussion During the first week of our experiment we were tasked with performing qualitative analysis on our unknown. Our plan was to make an assumption on what our unknown could possibly be after performing each of these tests from the selection of possible chemica ls. The first test we performed was the flame test, which gave us a yellow color. Based only on this we were able to eliminate numerous of the possible chemicals because they would have produced a different color flame, or no color at all. According to the Science Olympiad - sodium compounds, even in trace amounts, burn yellow. Our next test was conductivity, which revealed that our salt was indeed conductive.
Based on the conductivity numbers, paired with the flame test, we made the assumption that our unk nown was Sodium Hydroxide. Sodium Hydroxide is extremely conductive, and has a yellow flame. Once the PH test was completed, which gave us a PH of 10, we had a stronger feeling that our unknown was indeed Sodium Hydroxide, which generally has a PH of 13. W e attributed this difference to error in our PH reader, or other contaminants within our substance. Finally we analysed our solubility results, which provided us with further evidence that our compound was Sodium Hydroxide.
Sodium hydroxide is soluble in m ethanol, ethanol, and water. When we entered the lab for the second week of our project, we had a pretty solid assumption of what our unknown was. Week 2 gave us two options for quantitative tests we could have run. Volumetric was the better choice since our substance did not form precipitates and it was also very basic. The results showed us that Conclusion All of the data in the experiment points towards our unknown being Sodium Hydroxide, from the flame test to the appearance of the salt. We were able to make this educated assumption after thoroughly testing the unknown and analysing the results. After looking up the expected reactions of some typical substances, we concluded that our unknown is indeed Sodium Hydroxide. The ability to identify an inorg anic substance that is dissolved is extremely helpful in many situations, from finding a pollutant in a local water supply to testing the someones urine for illegal drugs. We were able to make a conclusion based on tests that are easily performed, with a m inimal amount of the unknown substance using characteristics that are unique to the chemical. References 1. Contaminant Identification Lab http://www.eag.com/contaminant -identification/ (accessed Mar 9, 2017). 2. 3. Research Connection