Some Common Techniques for Separation of a Mixture

1. Some Common Techniques for Separation of a Mixture

2. 1. Decanting Separate mixture by decanting Decant = To gently pour off a liquid without disturbing the sediment (solid) or denser liquid Sometimes you are trying to save the solid, sometimes the liquid, and sometimes you are trying to separate, but save, both! When trying to decant and save an aqueous solution, it is often poured slowly down a stirring rod. The stirring rod acts as a pathway to direct the liquid. This method works because of the large intermolecular forces (hydrogen bonding ) between water molecules. The strength of the H-bonding makes water molecules “sticky” – where one molecule goes the next is sure to follow.

3. 2. Gravity Filtration Let Gravity Do The Work!!! – Separate mixture by differences in solubility And let gravity do the work!!, the insoluble substance (unable to be dissolved) will be caught on the filter, the soluble (able to be dissolved) substances will pass through as part of the filtrate Pour liquid to be separated into filter paper

4. 3. Vacuum Filtration - Continued A special side-arm flask, called a Büchner Flask is used together with a special type of funnel called a Büchner Funnel The Büchner Flask is attached via a hose to a water nozzle and the water is turned on full blast! The rushing water creates a vacuum in the Büchner Funnel (Bernoulli’s Principle). The atmospheric pressure then ‘pushes’ the filtrate through the filter paper and funnel. The insoluble substance is left on the filter paper.

5. 4. Chromatography Separation mixture based on different migration rates due to differences in mass, size, charge, affinity for a substrate, or some combination thereof.

6. Paper Chromatography Solvent Front Filter paper sample solvent A piece of chromatography paper (the stationary phase) is ‘dotted’ with a sample of the mixture to be separated. The paper is placed into a solvent (the mobile phase) known to dissolve the sample. The paper will wick up the solvent via capillaryaction (liquid rising against gravity due to IMFs). The sample dissolves in the advancing solvent front. (c) The various constituents (parts) of the mixture move up at different rates based on their mass, size, charge, etc. Rf values are then analyzed to determine the compon- entsof the mixture

7. Paper Chromatography Chromatogram = the paper strip on which all or some of the constituents of a mixture have been separated by being adsorbed at different locations Origin= the point on the chromatography paper where the sample of the mixture is“dotted” Rf values = the ratio of the distance a compound moved from the origin to the distance between the origin and the solvent front. Stationary Phase (chromatography paper) Stationary Phase (chromatography paper) Starting Line Ink spots are centered, and evenly spaced on the starting line. Notice that the line and ink dots must be ABOVE the liquid level in the beaker when the paper is placed in contact with the mobile phase! If it were below the liquid level, the ink would wash out into the liquid! Starting Line Ink spots are centered, and evenly spaced on the starting line. Notice that the line and ink dots must be ABOVE the liquid level in the beaker when the paper is placed in contact with the mobile phase! If it were below the liquid level, the ink would wash out into the liquid! Beaker Beaker Mobile Phase (solution of NH3, butanol and water) Mobile Phase (solution of NH3, butanol and water)

8. 5. Evaporation Separate mixture by differences in boiling points Usually used to separate the constituents of a solution when the liquid portion, the solvent (thing that does the dissolving) has a much lower boiling point than that of the solid portion, the solute (thing that gets dissolved) This method is only good if there is no need to recover the solvent. Stationary Phase (chromatography paper) Stationary Phase (chromatography paper) Starting Line Ink spots are centered, and evenly spaced on the starting line. Notice that the line and ink dots must be ABOVE the liquid level in the beaker when the paper is placed in contact with the mobile phase! If it were below the liquid level, the ink would wash out into the liquid! Starting Line Ink spots are centered, and evenly spaced on the starting line. Notice that the line and ink dots must be ABOVE the liquid level in the beaker when the paper is placed in contact with the mobile phase! If it were below the liquid level, the ink would wash out into the liquid! Beaker Beaker Mobile Phase (solution of NH3, butanol and water) Mobile Phase (solution of NH3, butanol and water)

9. 6. Distillation Separate mixture by differences in boiling points Simple Distillation this method is used when all the components II. Fractional Distillation of a mixture must be recovered The different constituents in a mixture will boil at different temperatures based on their mass and/or polarity. More massive and/or polar substances will boil at higher temperatures than less massive and/or polar substances. Heating the mixture will, therefore, cause those substances with lower boiling temperatures to vaporize first. Lower boiling vapors can be collected and condensed to yield higher concentrations of that particular constituent of the mixture. Stationary Phase (chromatography paper) Stationary Phase (chromatography paper) Starting Line Ink spots are centered, and evenly spaced on the starting line. Notice that the line and ink dots must be ABOVE the liquid level in the beaker when the paper is placed in contact with the mobile phase! If it were below the liquid level, the ink would wash out into the liquid! Starting Line Ink spots are centered, and evenly spaced on the starting line. Notice that the line and ink dots must be ABOVE the liquid level in the beaker when the paper is placed in contact with the mobile phase! If it were below the liquid level, the ink would wash out into the liquid! Beaker Beaker Mobile Phase (solution of NH3, butanol and water) Mobile Phase (solution of NH3, butanol and water)

10. Distillation Usually used to separate solid solutes from their liquid solvent . The distillate is the purified solvent. The solutes remain in the distilling flask Stationary Phase (chromatography paper) Stationary Phase (chromatography paper) Starting Line Ink spots are centered, and evenly spaced on the starting line. Notice that the line and ink dots must be ABOVE the liquid level in the beaker when the paper is placed in contact with the mobile phase! If it were below the liquid level, the ink would wash out into the liquid! Starting Line Ink spots are centered, and evenly spaced on the starting line. Notice that the line and ink dots must be ABOVE the liquid level in the beaker when the paper is placed in contact with the mobile phase! If it were below the liquid level, the ink would wash out into the liquid! Beaker Beaker Mobile Phase (solution of NH3, butanol and water) Mobile Phase (solution of NH3, butanol and water)

11. 7. Magnetism Separate the components of a mixture based on differences in magnetism In a simple example, a mixture of iron filings and sulfur powder are separated from one another using a magnet. Stationary Phase (chromatography paper) Stationary Phase (chromatography paper) Starting Line Ink spots are centered, and evenly spaced on the starting line. Notice that the line and ink dots must be ABOVE the liquid level in the beaker when the paper is placed in contact with the mobile phase! If it were below the liquid level, the ink would wash out into the liquid! Starting Line Ink spots are centered, and evenly spaced on the starting line. Notice that the line and ink dots must be ABOVE the liquid level in the beaker when the paper is placed in contact with the mobile phase! If it were below the liquid level, the ink would wash out into the liquid! Beaker Beaker Mobile Phase (solution of NH3, butanol and water) Mobile Phase (solution of NH3, butanol and water)

12. Magnetism In a more complicated example, a magnet is used to bend the path of heavy and light (mass) charged particles (isotopes, molecules, molecular fragments) to separate the components of a mixture on an atomic or molecular level. The equipment used to accomplish this is called a mass spectrometer. Stationary Phase (chromatography paper) Stationary Phase (chromatography paper) Starting Line Ink spots are centered, and evenly spaced on the starting line. Notice that the line and ink dots must be ABOVE the liquid level in the beaker when the paper is placed in contact with the mobile phase! If it were below the liquid level, the ink would wash out into the liquid! Starting Line Ink spots are centered, and evenly spaced on the starting line. Notice that the line and ink dots must be ABOVE the liquid level in the beaker when the paper is placed in contact with the mobile phase! If it were below the liquid level, the ink would wash out into the liquid! Beaker Beaker Mobile Phase (solution of NH3, butanol and water) Mobile Phase (solution of NH3, butanol and water)

13. Vocab • Affinity • Büchnerflask • Büchnerfunnel • Capillary action • Chromatogram • Chromatography • Chromatography, paper • Condensate • Condenser • Constituent(s) • Decant(ing) • Distillate • Distillation • Distilling flask • Filtrate • Filtration • Filtration, gravity • Filtration, vacuum • Hydrogen bonding (H-bonding) • Insoluble • Intermolecular forces (IMFs) • Mass spectrometer • Miscible • Mobile phase • Sediment • Soluble • Solute • Solution • Solvent • Solvent front • Stationary phase • Substrate • “Wick up”