When a mixture of water, sand, and salt is filtered, what passes through the filter paper?

2 Answers
Mar 29, 2018

The water and salt passes through the filter.


This happends because the salt dissolves into the water and the sand dosent pass through the filter. Theirfore the only the salt and water pass through.

Mar 30, 2018

If the salt is fully dissolved then it, plus the water passes through the filter paper.


A mixture of salt fully dissolved in water only contain particles whose sizes are on the ionic or molecular scale, whereas the finest filter paper grades (e.g. 602h) have pore sizes of around 2 micron. That’s at least 10,000 times larger than molecular scale.

Sand on the other hand, can have particle size up to millimetre scale (1000 times larger than the fine filter paper pore size) so it doesn’t pass through.

But be careful with terminology - a “mixture” of water sand and salt doesn’t automatically mean that the salt is dissolved. It could be a mixture where only half the salt has dissolved; in such a case the undissolved salt wouldn’t pass through the filter paper.