Identification of Anions and Cations

Experiment #5 Identification of Anions and Cations Data and Results Post-Laboratory Questions 1. Each of the following samples contains ONLY ONE of the two chemicals shown. If you were to carry out only ONE of the confirmatory tests from the experiment, specify the reagent(s) you would use to identify which chemical is present. Justify your choice of reagent(s) by explaining the two possible outcomes from the ONE test. 1.1 Na2SO4 and NaI The reagent I would use for the reaction is the barium chloride. According to the solubility rules and the experiment, when the ion Ba+2 is paired with sulfate, the reaction should form a white precipitate. If no precipitate is formed, it means that there is no sulfate in the reaction. BaCl2 (aq) + Na2SO4 (aq) → BaSO4 (s) + 2 NaCl (aq) BaCl2(aq) + 2 NaI(aq) → BaI2(aq) + 2 NaCl(aq) 1.2 Fe(NO3)3 and Zn(NO3)2 The reagent I would use for this sample is NH3. If Fe(NO3)3 reacts with NH3, then the solution will form a brown precipitate. If no precipitate is formed, then no Fe(NO3)3 is present, only Zn(NO3)2. 1.3 K3PO4 and Na2CO3 The reagents I would use for this reaction are HNO₃ and (NH4)2MoO4. If the reagents are mixed with Na2CO3, then no precipitate will form. However, if the reagents are mixed with K3PO4, then a yellow precipitate will form. 2. How would you go about testing for the presence of SO42- in the presence of NO3-? According to the solubility rules, when a Ba+2 ion is paired with SO42-, forming BaSO4, then the compound is insoluble. However, when the same ion is paired with NO3-, forming Ba(NO3)2, then the compound is soluble. Therefore, I would add BaCl2 to the solution. If a precipitate is formed, that confirms the presence of SO42-. If a precipitate is not formed, then there is no SO42-. 3. In the CO3-2 test, what is the milky solid (white solid in suspension) that forms in the limewater solution? Use chemical equations to show the formation of the white solid. First of all, the CO3-2 is tested with 1 mL of dilute HCl, which means that CO2 will be released. This leads us to this equation: CO3-2 + 2 H + CO2 + H2O Then, the CO2 that is released will react with limewater, which leads us to this equation: Ca(OH)2 (aq) + CO2 (g) → CaCO3 (s) + H2O (l) As we can observe from the equation of the reaction here, the white milky solid formed is CaCO 3(s). 4. In the test for I−, you use methylene chloride. How does the density of methylene chloride compare to the density of water? The density of methylene chloride (CH2Cl2) is of 1.33g/mL. The density of water is of 1g/mL. If we compare the two densities, we can conclude that the methylene chloride is denser. To further support this thesis, after some calculations involving the molecular masses of each compound, you can arrive at the conclusion that methylene chloride is denser than water since the mass of methylene chloride is equal to 85g/mol, whereas the mass of water is equal to 18g/mol. 85g/mol is greater than 18g/mol. Therefore, we can safely conclude that methylene chloride is denser than water. Moreover, we can conclude that the reason the purple color appeared in the bottom layer of the test tube is because the iodine’s density is higher than that of the water. A liquid with higher density will always sink in the liquid with the lower density. Flow Chart Fe+3 Al3+ 1- Add 1 mL of Fe+3 to the test tube. 2- Add 10 drops of 6 M NH3. 3- End of reaction: Brown precipitate. 12345- Zn+2 12345+2 Mg 1234- Add 1 mL of Al3+ to the test tube. Add 0.5 mL of 6 M HCl. Add 1-2 drops of aluminon reagent with 6 M NH3 dropwise until it is basic. Centrifuge the solution. End of reaction: Red precipitate. Add 1 mL Zn+2 of to the test tube. Add 6 M HCl dropwise. Add 3 drops of 0.2 M C₆FeK₄N₆. Stir with the rod. End of reaction: Light green precipitate. Add 1 mL of Mg+2 to the test tube. Add 3 drops of magneson reagent. Add 6 M NaOH solution dropwise. End of reaction: Blue precipitate. I− 1- Add 1 mL of the product to the test tube. 2- Add 6 M HCl solution dropwise until it becomes acidic. 3- Add 1 mL of FeCl3 and 1 mL of methylene chloride. Mix the solution 4- End of reaction: Becomes purple. SO₄²1- Add 1 mL of the product to the test tube. 2- Add 1 mL of 6 M HCl dropwise until it becomes acidic. 3- Add 1 mL of BaCl2 solution. Mix well 4- End of reaction: Formation of a white solid. ³PO4 1- Add 1 mL of the product to the test tube. 2- Add 1 mL of 6 M HNO₃. 3- Add 1 mL of 1 M (NH4)2MoO4 solution. 4- Put it in the boiling water for 2 minutes. 5- End of reaction: Yellow precipitate. CO3-2 1- Put 1 mL of Ca(OH)₂ (aqueous) in the medium test tube. 2- In the 2nd test tube, add 1 mL of the CO3-2. 3- Add 1 mL of 6 M HCl gently down the sides of the test tube with the dropper. The solutions must be unmixed. 4- Fit a glass bend into the 2 test tubes (see figure 1). 5- Shake the test tube. 6- End of reaction: Bubbles and milky solid in the lime water.