What are physical properties that can separate a mixture?

1 Answer
Jun 6, 2018

Examples might include

  • Soluability
  • Immiscibility
  • Boiling point

Explanation:

Table salt #"NaCl"# dissolves well in water whereas sand- a mixture containing primarily quartz #"SiO"_2#- does not. The difference in the solubility of the two species enables their separation through filtration.

http://www.rsc.org/learn-chemistry/content/filerepository/CMP/00/000/455/CCE-1-SeparatingASandAndSaltMixture.pdf

For example, to separate a mixture of sand and table salt, start by dissolving the solid mixture in water to form a #"NaCl"# solution that contains sand. The solution part shall pass through a piece of filter paper whereas sand will be trapped on the funnel. Evaporating the salt solution removes #"H"_2"O"# such that #"NaCl"# is restored to its crystal form.

Separation funnels (see diagram below) facilitates the separation of two immiscible liquids - liquids that don't dissolve in each other e.g., water and mineral oil.

http://www.bbc.co.uk/schools/gcsebitesize/science/add_edexcel/covalent_compounds/seperationrev1.shtml

What if the two liquids dissolve in each other in significant amounts? Fractional distillation separates substances of different boiling points. For example, it is possible to isolate ethanol #"C"_2"H"_5"OH"# from its solution in water #"H"_2"O"#- the two liquids mix at any ratio due to their capabilities of forming hydrogen bonds- with the help of distillation given that ethanol boils at a temperature lower than that of water.

https://commons.wikimedia.org/wiki/File:Fractional_distillation_lab_apparatussvg

In the particular setup shown in the diagram, the temperature of the mixture in the round-bottom flask is maintained between #78.37color(white)(l)°"C"# the boiling point of ethanol and #100color(white)(l)°"C"# the boiling point of water, such that ethanol vaporizes, leaves the mixture, condenses, and collects in the conical flask whereas water remains in the mixture.