A mixture contains solid potassium nitrate (KNO3) and a small amount of manganese dioxide (MnO2), which is insoluble in water. Which sequence of steps is most appropriate to obtain pure potassium nitrate from the mixture?
Show the answer and explanation
Correct answer
A. Add water, filter, evaporate the filtrate to dryness.
Principle or equation
Potassium nitrate is soluble in water, while manganese dioxide is insoluble. Filtration separates the insoluble solid from the solution. Evaporation of the filtrate yields solid potassium nitrate.
Why this answer is correct
The mixture is stirred with water to dissolve KNO3. The insoluble MnO2 is removed by filtration. The filtrate contains dissolved KNO3, and evaporation of the water leaves pure KNO3. Recrystallization could further purify, but evaporation to dryness is sufficient for obtaining the salt from the solution.
Example
If 10 g of the mixture is added to 50 mL water, KNO3 dissolves, MnO2 remains. Filter to remove MnO2, then evaporate the filtrate to obtain KNO3 crystals.
This published item includes a stored explanation and passed the platform’s publication workflow. It is independent preparation material, not a claim of an official or recalled examination question.