About this experiment
Assemble a funnel and filter paper above a receiving beaker, then pour a salt-and-sand mixture. Dissolved salt follows the water, while an intact filter retains the sand. Inspect both fractions to see why a clear filtrate is not necessarily pure water.
Learning goals
- Distinguish a dissolved substance from suspended particles.
- Balance material among feed, retained solid and filtrate.
- Compare an intact filter with a damaged or missing one.
How to use it
- 1Assemble the filter and pour part of the mixture. Inspect water, salt and retained sand readouts.
- 2Complete the pour and check that all dissolved salt has entered the receiver.
- 3Repeat with the torn-paper model and with no paper. Compare sand in the filtrate.
- 4Change starting masses, record the outcomes and verify that each material is accounted for.
The model
Assumptions
- All selected salt is already dissolved, and water density is treated as 1 g/mL. The selected salt range is below its saturation limit in the selected water volume.
- Intact paper retains all suspended sand; the torn-paper teaching model retains 20 percent; no paper retains none. These are prescribed retention cases, not a calibrated pore-size model.
- Transfer progress is the fraction of starting mixture processed. Dissolved salt and water move together. Filter hold-up, adsorption, evaporation and changing flow resistance are excluded.
Try this in class
- Q1How could the dissolved salt be separated from the clear filtrate after filtration?
- Q2Why does a torn filter change suspended sand but not the dissolved-salt fraction?
Frequently asked questions
Does clear filtrate mean all substances except water were removed?
No. Dissolved salt passes through the filter with water in this model.
What remains in the source before a complete pour?
The unprocessed fraction still contains its proportional water, salt and sand. Retained sand counts only particles already processed by the paper.