KEY2CHEM

Separation Experiments

Often it is desirable to separate a mixture into its individual components. An example would be purifying gold from its ore or treating wastewater to reduce its environmental impact. Depending on the nature of the solute and solvent, many different separation techniques are available.

Example 1.

A mixture contains $$\require{mhchem}\ce{PbS(s)}$$ and $$\require{mhchem}\ce{K2S(aq)}$$ in an aqueous solution. Which technique would allow for effective separation of these two compounds?

A. filtration

B. distillation

C. chromatography

Solution

A. filtration

Filtration is often an simple and effective method for separation of solids and liquids (including aqueous solutions).

Example 2.

A chemist would like to separate two liquid hydrocarbons having different molar masses. Which technique would allow for most effective separation?

A. filtration

B. distillation

C. chromatography

Solution

B. distillation

Since both compounds are liquids, filtration will not effectively separate them. As hydrocarbons, they are both nonpolar molecules with dispersion forces as the strongest type of intermolecular force, and chromatography will not permit effective separation. Since they have different molar masses, they’ll have differing strength of dispersion forces (and therefore different boiling points) and distillation can be used to separate them.

Example 3.

Black pen ink is often made from a blend of other colors. You want to separate the ink into its individual colors. Which technique would allow for most effective separation?

A. filtration

B. distillation

C. chromatography

Solution

C. chromatography

Chromatography would allow for relatively easy separation, based on how strongly each ink interacts with the stationary and mobile phase. Since the inks are visible, their separation progress can be visualized during the chromatography experiment.