3 III. Data Collection (8 pts): Tests of the Supernatants A. Obtain dropper bottles of 0.3 M Na 3 PO 4 and 1 M HCl and about 1 cm 3 of solid KI. [Note- a teaspoon is about 5 cm 3 .] Place about 1 mL of the stock Ca(NO 3 ) 2 and KIO 3 solutions in separate test tubes. Ca 2+ test: Add about 10 drops ( 1 / 2 mL) of Na 3 PO 4 solution to the 1 mL of Ca(NO 3 ) 2 solution. Describe the results. The reaction is: 3 Ca 2+ (aq) + 2 PO 4 3- (aq) Ca 3 (PO 4 ) 2 (s) IO 3 - test: Dissolve about 1 / 2 cm 3 of KI into the 1 mL of KIO 3 solution; then add about 1 mL (20 drops)of 1 M HCl. Describe the results. The reaction is IO 3 - (aq) + 5I - (aq) + 6H + (aq) 3I 2 (aq) + 3 H 2 O B. Using these tests, check the two supernatants from part II.A. for the presence of Ca 2+ and the presence of IO 3 - . Describe the results. Supernatant 1 Supernatant 2 Ca 2+ test Observation Conclusion IO 3 - test Observation Conclusion IV. Dropwise Mixing (4 pts) Using a dropper add the stock Ca(NO 3 ) 2 solution 5 drops at a time to your remaining sample of stock KIO 3 solution. After each addition, stir with scratching (rubbing the stirring rod against the beaker bottom or sides) and record your observations. Continue with additions until you have definitely produced a precipitate.
4 V. Data Analysis (8 pts) A. How do the actual precipitate masses compare to the masses you predict by calculation? Calculate your % yield. Make a list of at least 5 possible explanations for a % yield that is not 100%. B. Are the test results for the presence of Ca 2+ and IO 3 - in the supernatants consistent with the limiting reactant calculations in part II.B? Report any inconsistencies between the calculated and test results. Explain your reasoning. What explanations, given in A, also explain the results for tests on ions in the supernatant? What explanations fail to account for the tests on the supernatants? Do you need an additional explanation? Explain your reasoning.
5 C. Were the results of the Dropwise Mixing experiment unexpected?
- Summer '20
- Solubility, Reagent, Precipitation