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Difficulty: MediumFiltration, Evaporation, and Crystallization

A laboratory mixture contains soluble potassium trioxonitrate(V) (KNO3\text{KNO}_3) contaminated with insoluble clay particles. What is the correct sequential order of operational steps required to obtain pure, dry crystals of KNO3\text{KNO}_3 from this mixture?

  1. 1Dissolve the impure mixture in warm distilled water with continuous stirring.
  2. 2Filter the mixture using filter paper and a glass funnel.
  3. 3Heat the clear filtrate gently in an evaporating dish until it reaches its saturation point.
  4. 4Allow the hot saturated filtrate to cool down slowly, then filter and dry the formed crystals between filter papers.

Answer

The correct sequential order of operational steps is: First, dissolve the impure mixture in warm distilled water with continuous stirring. Second, filter the mixture using filter paper and a glass funnel. Third, heat the clear filtrate gently in an evaporating dish until it reaches its saturation point. Fourth, allow the hot saturated filtrate to cool down slowly, then filter and dry the formed crystals between filter papers.
To separate and purify a soluble salt mixed with an insoluble solid, dissolution must occur first so that the salt enters the liquid phase while the insoluble component remains solid. Filtration then isolates the solid residue from the dissolved salt filtrate. The filtrate is heated only until it becomes saturated; subsequent slow cooling lowers solute solubility and allows pure crystals to precipitate cleanly without thermal degradation.

Step-by-Step Solution

1
Dissolve the mixture in distilled water.
A aqueous mixture containing dissolved KNO3\text{KNO}_3 and suspended insoluble clay is formed.
Solubility differences allow the soluble salt to dissolve while insoluble impurities remain solid.
2
Filter the mixture through filter paper.
Insoluble clay is retained on the paper as residue, yielding clear aqueous KNO3\text{KNO}_3 filtrate.
Filtration separates undissolved solid matter from liquid solution based on particle size.
3
Evaporate water until the solution is saturated.
A hot saturated solution of KNO3\text{KNO}_3 is produced.
Evaporating solvent increases solute concentration until the crystallization point is achieved.
4
Cool the saturated solution slowly and dry the resulting precipitate.
Pure KNO3\text{KNO}_3 crystals form and are isolated dry.
Solubility decreases upon cooling, causing the dissolved salt to crystallize out of solution cleanly.

Key Concept

Sequential purification of soluble salts from insoluble solids using dissolution, filtration, concentration to saturation, and crystallization.
Estimated Time:1m 30s
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Topics

Filtration, Evaporation, and Crystallization