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Difficulty: MediumFiltration, Evaporation, and Crystallization

A solid mixture contains insoluble barium sulfate (BaSO4\text{BaSO}_4) and soluble potassium trioxonitrate(V) (KNO3\text{KNO}_3). Which of the following procedures should be used to recover pure crystals of KNO3\text{KNO}_3 from the mixture?

  1. Add water to dissolve the mixture, filter off the residue, heat the filtrate until a saturated solution is formed, and allow it to cool slowly.Answer
  2. B
    Add water to dissolve the mixture, filter off the residue, and heat the filtrate strongly until all water evaporates completely to dryness.
  3. C
    Add water to dissolve the mixture, collect the residue on the filter paper as potassium trioxonitrate(V), and discard the filtrate.
  4. D
    Heat the solid mixture directly to evaporate barium sulfate and leave pure potassium trioxonitrate(V) in the container.

Answer

Add water to dissolve the mixture, filter off the residue, heat the filtrate until a saturated solution is formed, and allow it to cool slowly.
Dissolving the mixture in water solubilizes potassium trioxonitrate(V) while leaving barium sulfate insoluble. Filtering removes the solid barium sulfate as a residue. Heating the filtrate to saturation and cooling it slowly allows pure crystals of potassium trioxonitrate(V) to precipitate out.

Step-by-Step Solution

1
Separate insoluble solid from soluble solid using water.
Barium sulfate (BaSO4\text{BaSO}_4) remains insoluble while potassium trioxonitrate(V) (KNO3\text{KNO}_3) dissolves completely.
Difference in solubility allows physical separation.
2
Filter the mixture.
Barium sulfate is collected on the filter paper as the residue, and the aqueous solution of potassium trioxonitrate(V) passes through as the filtrate.
Filtration separates insoluble solids from liquids.
3
Concentrate the filtrate to saturation and cool slowly.
Pure crystals of potassium trioxonitrate(V) precipitate out of solution.
Crystallization yields pure, well-formed crystals without thermal decomposition or loss of hydration structure.

Key Concept

Separation of soluble and insoluble solids by dissolution, filtration, and crystallization.
Estimated Time:1m 30s
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Topics

Filtration, Evaporation, and Crystallization