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Name: Brittany
Status: student
Grade: 9-12
Location: N/A
Country: N/A
Date: September 2006

Question:
Can filtration and evaporation determine whether mixtures are suspensions and solutions?



Replies:
Brittany,

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.

Matt Voss



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.

Vince Calder


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