Filtration, Evaporation, Suspensions, and Solutions
Date: September 2006
Can filtration and evaporation determine whether
mixtures are suspensions and solutions?
For the most part yes, but you have to be careful about how you
perform your experiments. There are some suspensions that contain
very fine particles and will filter right through filter paper--so
knowing the pore size of your filter paper is important. 0.45um is
a fairly standard pore and should filter off most solids. There are
also mixtures like emulsions (ie mayonnaise) that will not filter or
evaporate. If you are just trying to discern suspensions and
solutions, then you will not have to worry about emulsions.
Filtration will separate mixtures that are suspensions, provided
that the particle size of the suspended material is larger than the
average, i.e. nominal pore size of the filter medium. Dissolved
materials will not be retained by a filter membrane. This assumes
that the viscosity of the solution does not change the time scale of
the filtration process. I know this sounds like a lot of evasive
conditions, but that is how things happen. Evaporation or course
retains all undissolved, and possibly dissolved substances, if the
solubility of the particular substances is exceeded. I know this
sounds evasive, but the question has a lot of "if, and, buts"
associated with it. One has to deal with the various possibilities
on a case-by-case basis.
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Update: June 2012