Lab 4 5 Vitamin Examination Laboratory Goals In this lab you will Learn how to test for cations and anions in a solution Use the inorganic material tests to analyze a multi vitamin Safety Notes You will be working with concentrated acids and bases NaOH pellets and other potentially harmful materials Keep in mind that acids and bases of this strength can cause permanent damage especially to eyes WEAR SAFETY GOGGLES AT ALL TIMES You will also be using Bunsen burners BE CAREFUL Introduction In the past we have done a quantitative analysis where we found out how much of a substance is present in a sample In this lab you will be performing a qualitative analysis on a vitamin This process allows you to determine what is present in a sample Most of the tests in this lab will utilize the solubility rules to determine the presence of anions or cations Other tests will require adding a chemical to shift the equilibria as explained by LeCh telier s Principle For each of these tests you will use known compounds to determine what each a positive and negative test looks like prior to performing the same tests on your vitamin sample There are two parts to this lab You should work in pairs though try to work with someone with whom you have not previously worked In Part One you will be testing two solutions A and B and distilled water Solution A will contain the cations Ca 2 Na Fe 3 NH4 and Zn 2 Solution B will contain the anions Cl I PO4 3 and SO4 2 The solutions will show you what positive tests look like The distilled water will show you what negative tests look like In Part Two you will prepare and analyze the multi vitamin sample In this laboratory you will be using the centrifuges to quickly separate suspensions Whenever you are using a centrifuge it is critical that you counterbalance the machine This means that in addition to your test tube of material that you are trying to separate it is critical that you insert a second test tube of equal weight to the one you are trying to separate i e containing the same amount of liquid in the hole directly opposite your sample tube before spinning If the weight of the two tubes is not close there is a good chance that one or both of the two tubes will break and in addition to preventing anyone else from using the machine you will get the joy of cleaning up the broken glass and spilled chemicals For this reason the lid must also be closed anytime the centrifuge is in use Keep in mind that NOT turning the centrifuge to the maximum speed will significantly reduce the likelihood of catastrophic misbalancing 30 Procedure Part One Testing the Methods A Test for calcium ions Add 1 mL of Solution A to a test tube and 1mL of distilled water to a second test tube Centrifuge for two minutes if no solid is present you may skip this step Transfer both liquids into different test tubes to discard any precipitate Pour a small an equal amount of 0 25M ammonium oxalate into the test tubes Record the appearance of both test tubes Solution A should become cloudy or form a white precipitate indicating a positive test for calcium B Test for sodium ions Dip a wire loop into Solution A hold the wire loop over a Bunsen burner flame Dip the wire loop into distilled water and hold it over the flame Record the color of both flames Solution A should turn the flame orange Remember that this is the same test that you used last semester to look at different cations in solution Note Sodium gives a very sensitive and distinctive flame test Because of its sensitivity even trace amounts of sodium ions will give a yellow coloration to the flame Since traces of sodium can easily come from a variety of sources including residual amounts on the wire loop you should be able to detect the difference between a positive test and what might be mistaken for a positive test C Test for iron III ions Iron is commonly found as either Fe2 or Fe3 Unfortunately the iron test outlined in this experiment will not detect Fe2 In order to obtain a positive result for iron in the 2 state it is necessary to oxidize it to the 3 state prior to testing Place 2 3 mL of Solution A in at test tube and add in a couple crystals of ammonium persulfate and swirl to dissolve If Fe2 is present in solution the following redox reaction will occur S2O82 aq 2 Fe2 aq 2 SO42 aq 2 Fe3 aq Add a few drops of this solution to one well in the wellplate and distilled water to another Add a few drops of 0 1 M sodium thiocyanate A red color indicates the presence of Fe III ions due to the formation of FeSCN2 If you do not see a red color add 2 drops of 6M HCl and recheck Note This test is very sensitive to trace impurities of Iron You may wish to test your anion solution B and note the difference in intensity that may occur from impurities D Test for zinc ions Add a few drops of Solution A to a well plate and distilled water to a separate well Add one drop of 6 0M HCl and three drops of 0 2M potassium ferrocyanate to each well A grayish white to bluish green precipitate of Zn3K2 Fe CN 6 2 indicates the presence of zinc ions 31 E Test for ammonium ions Place one sodium hydroxide pellet in two beakers 50 mL is a good size for this Place a piece of wet pH paper on the bottom of two different watchglasses Add three drops of Solution A to a beaker with the sodium hydroxide and three drops of distilled water to the other Cover the beakers with the watchglass such that the pH paper above the liquid A deep blue color indicates the alkalinity of the NH3 fumes released from the beaker The pH paper then reacts with the OH ions released when the ammonia reacts with the water on the pH strip F Test for chloride and iodide ions Add 1 mL of Solution B to a test tube and 1 mL of distilled water to another Add 2 drop of 6 0M HNO3 and an equal amount of 0 1M silver nitrate to each test tube A precipitate indicates the presence of either Cl and or I AgCl s is white and AgI s is yellow so you may have a guess of which ion s you have based on the color To be sure more tests are required Centrifuge for two minutes and discard the supernatant liquid Add 6 0M NH3 to make the solution strongly basic and dissolve as much of the precipitate as possible the AgCl s will be in equilibrium with Ag NH3 2 aq whereas a AgI s does not detectably form the ammonia complex If all the …