A laboratory technician needs to recover pure hydrated copper(II) tetraoxosulfate(VI) crystals () from an aqueous suspension containing insoluble copper(II) oxide residue. Which of the following procedures correctly describes the optimal method to obtain the dry, hydrated crystals?
- Filter the mixture to remove insoluble copper(II) oxide, concentrate the filtrate by gentle heating until saturation, allow the saturated solution to cool for crystallization, and dry the crystals between filter papers.Answer
- BFilter the mixture to remove insoluble copper(II) oxide, then evaporate the filtrate completely to dryness over a strong direct flame to obtain anhydrous powder.
- CEvaporate the unfiltered suspension to complete dryness first, then add distilled water to dissolve the solid, and filter off the remaining liquid.
- DFilter the mixture, discard the filtrate, collect the residue on the filter paper, and dry the residue in an oven.
Answer
Filter the mixture to remove insoluble copper(II) oxide, concentrate the filtrate by gentle heating until saturation, allow the saturated solution to cool for crystallization, and dry the crystals between filter papers.
Filtration removes insoluble solid residue from the solution. Heating the filtrate only until a saturated solution is obtained, followed by controlled cooling, enables the formation of hydrated copper(II) tetraoxosulfate(VI) pentahydrate crystals () without destroying the water of crystallization.
Step-by-Step Solution
Key Concept
Distinction between evaporation to dryness and crystallization for thermally sensitive or hydrated salts