Some Common Techniques for Separation of a Mixture

1. Some Common Techniques for Separation of a Mixture

2. 1. Decanting Let Gravity Do The Work!!! – Separate mixture by differences in solubility or density 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. Paper chromatography Thin Layer Chromatography Gel Filtration Chromatography Gas Chromatography

6. I. Paper Chromatography Solvent Front Filter paper sample solvent A simple piece of filter paper has been ‘dotted’ with a sample to be separated. The filter paper is placed into a solvent known to dissolve the sample. The filter paper will wick up the solvent via capillaryaction (liquid rising against gravity). 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.

7. II. Thin Layer Chromatography Similar in principle and method to simple paper chromatography, a glass plate coated with a filtering substance, called the stationary phase, is used instead of filter paper. The solvent, called the mobile phase , carries the mixture to be separated through the stationary phase. The components of the mixture are separated based on mass, size, charge, etc.

8. II. Thin Layer Chromatography – Con’t Glass plates overlain with a silica gel stationary phase Glass plates being covered with a stationary phase made of a corn starch slurry 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. III. Gel Filtration Chromatography Buffer Substance capable of neutralizing acids and/or bases w/o appreciably changing the overall acidity or alkalinity of the solution Elute exit from, or remove by dissolving Equilibrate to balance equally, or come into equilibrium with pore small opening 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. IV. Gas Chromatography Mixture is vaporized – the vapors of the various constituents of the mixture move along a gasflow, the mobile phase, at different rates based on their affinity (compatibility) for the stationary phase. Thus, the components arrive at the detector at different times. In many cases the identity of the constituents can be made based on the differing amounts of times that they are ‘retained’ (the retention time, or RT) in the column (the stationary phase.) The result is a gas chromatogram, a ‘picture’ of the relative amounts of substances present in the mixture. Chromatogram = the column, gel layer, paper strip, etc. on which all or some of the constituents of a mixture have been separated by being adsorbed at different locations 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. 4. 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)

12. 5. 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)

13. I. Simple 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)

14. II. Fractional Distillation Used to separate mixtures of miscible (mixable) liquids The different liquids are called fractions, and their boiling points are close to one another The vapors are cooled and condensed by the beads of the fractionating column. The condensed liquid (condensate) is already more concentrated in one substance (the one with the lower bp) than the other. Fresh hot vapors wash over and re-vaporize the condensate. The new vapors moves a little higher up the fractionating column before they once again cool and condense – now a little more concentrated than last time. This process of vaporization – condensation is repeated over and over again until almost pure vapors of one substance elute from the top of the fractionating column. They are then cooled in the condensing unit and a VERY pure distillate emerges. 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)

15. II. Fractional Distillation – Con’t. Fractional Distillation is used to refine crude oil. Through the repeated process of vaporization-condensation, lighter hydrocarbons emerge from higher up the fractionating column while heavier hydrocarbons concentrated at the bottom . Hydrocarbons Compounds or mixtures of compounds containing only the elements hydrogen and carbon 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)

16. 6. 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)

17. 6. Magnetism - Continued 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)

18. Vocab • affinity • Büchner flask • Büchner funnel • buffer • capillary action • chromatogram • chromatography • chromatography, paper • chromatography, thin layer • column • condensate • condenser • constituent(s) • decanting • distillate • distillation • distillation, fractional • distillation, simple • distilling flask • elute • equilibrate • filtrate • filtration • fraction • fractionating column • hydrocarbon • hydrogen bonding (H-bonding) • insoluble • intermolecular forces • mass spectrometer • miscible • mobile phase • pore • retention time • sediment • soluble • solute • solution • solvent • solvent front • stationary phase • wick up