Learning focus
Develop safe and reproducible practical methods, record precise observations and measurements, process evidence and evaluate experimental quality.
Principle
Filtration separates an insoluble solid from a liquid. The filter paper has pores that allow liquid and dissolved particles through but retain larger solid particles.
Products
The solid on the paper is the residue. The liquid collected is the filtrate. A dissolved solute passes through and is not removed by ordinary filtration.
Washing
Wash a precipitate with small portions of distilled water to remove soluble impurities. Too much water may dissolve some product if it has slight solubility.
Drying
Dry between filter papers, in a warm place or by an appropriate controlled method. Heating strongly may decompose a hydrate or product, so the method should suit the substance.
Practical or data skill
Draw and label a filtration setup and explain how to recover a pure dry precipitate.
Examination tip
Filtration cannot separate a dissolved salt from water.
Review questions and suggested answers
Question 1
What is the residue?
Suggested answer
The solid retained by the filter.
Question 2
What is the filtrate?
Suggested answer
The liquid that passes through.
Question 3
Why wash a precipitate?
Suggested answer
To remove soluble impurities.
