CHEMISTRY · Multi-part · AP · Chemistry · Chemical Reactions · Chemical Reactions
Problem
During a first-week laboratory exercise, students are asked to separate and analyze a mixture containing sodium chloride, calcium carbonate, and copper(II) sulfate pentahydrate. The procedure and observations are summarized below.
Step A. The dry mixture is ground to a fine powder and then passed through a mesh screen; particle size decreases, and blue color is uniformly distributed.
Step B. The powder is slowly heated to 120 °C until mass remains constant; faint steam is observed escaping.
Step C. The warm solid residue is added to distilled water and stirred; the solution turns light blue, and an insoluble white solid settles over time.
Step D. Dilute hydrochloric acid is added to the mixture from step C with gentle stirring; vigorous bubbling occurs, and the white solid disappears.
Step E. The resulting clear blue solution is evaporated to dryness on a hot plate at 105 °C, yielding blue crystals.
Use the information above to analyze the nature of the changes in each laboratory step.
(a) For each step (A–E), indicate whether the principal change is physical, chemical, or a combination. Provide explicit reasoning that references the recorded observations.
(b) For any step you classified as chemical, write a balanced chemical equation (symbolic or net ionic, as appropriate) that represents the major reaction(s).
(c) Quantitative data show that the sample mass decreases by 5.7 % in step B. Propose a chemical species responsible for the mass loss and explain, with reference to the crystal structure of copper(II) sulfate pentahydrate, why your proposal is consistent with both the mass change and the observation of steam.
(d) Design an additional single test that could confirm whether step E restored the pentahydrate form of copper(II) sulfate. Describe the expected result for both positive and negative outcomes and explain how each outcome would influence your classification of step E.