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Difficulty: HardFiltration, Evaporation, and Crystallization

Match each separation requirement on the left with the most appropriate physical separation technique on the right.

  • Obtaining insoluble suspended chalk powder from an aqueous mixtureFiltration
  • Recovering solid anhydrous sodium chloride from brineEvaporation to dryness
  • Obtaining pure hydrated iron(II) tetraoxosulfate(VI) crystals from an aqueous solutionCrystallization
  • Separating a mixture of potassium trioxonitrate(V) and potassium chloride based on temperature-dependent solubility differencesFractional crystallization

Answer

The correct pairings match chalk suspension with filtration, anhydrous sodium chloride recovery with evaporation to dryness, hydrated iron(II) tetraoxosulfate(VI) recovery with crystallization, and separating multiple soluble salts of varying temperature dependence with fractional crystallization.
Filtration is used for insoluble suspended solids (chalk). Evaporation to dryness is appropriate for thermally stable, non-hydrated solutes (sodium chloride). Crystallization prevents thermal decomposition and preserves water of crystallization in heat-sensitive salts (hydrated iron(II) tetraoxosulfate(VI)). Fractional crystallization separates multiple dissolved salts based on differences in their solubility curves at varying temperatures.

Step-by-Step Solution

1
Examine the solubility of the component to be separated from the liquid medium.
Chalk is insoluble and forms a suspension, whereas sodium chloride, hydrated iron(II) tetraoxosulfate(VI), potassium trioxonitrate(V), and potassium chloride dissolve completely.
Insoluble solids are separated mechanically via filtration, whereas dissolved solutes require thermal or solubility-based techniques.
2
Assess the thermal stability and hydration requirements of single dissolved solutes.
Sodium chloride is thermally stable and recovered as an anhydrous salt, while hydrated iron(II) tetraoxosulfate(VI) (FeSO4⋅7H2O\text{FeSO}_4\cdot7\text{H}_2\text{O}) loses its water of crystallization and decomposes under strong heat.
Thermally stable salts can be evaporated to dryness, whereas thermally labile or hydrated salts require gentle concentration followed by cooling (crystallization).
3
Evaluate solutions containing multiple soluble solid solutes.
Potassium trioxonitrate(V) (KNO3\text{KNO}_3) and potassium chloride (KCl\text{KCl}) have distinct solubility curves across temperatures.
Fractional crystallization selectively precipitates the less soluble component at a given temperature while leaving the more soluble component in solution.

Key Concept

Selection criteria for filtration, evaporation to dryness, crystallization, and fractional crystallization based on solute solubility, thermal stability, hydration state, and temperature dependence.
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Topics

Filtration, Evaporation, and Crystallization