00:00:00 Thank you for watching.

00:00:31 Erlenmeyer flasks are ideally adapted to the major operations of crystallization.

00:00:39 Suction filtration requires a suction funnel fitted by a neoprene adapter to a filter flask and fitted with a paper of appropriate size.

00:00:49 This large flask stands up by itself when attached to the heavy suction tubing, but a little flask needs support.

00:01:00 Provided by a filter block.

00:01:04 The next size flask is supported by crimping the tubing in only at the far end of the groove.

00:01:12 A filter trap is required to prevent frothing over from the filter flask or a suck back from the suction pump.

00:01:20 For quick release of suction to stop foaming, this pressure release device is made by thrusting a section of thin wall tubing into a spring clothespin.

00:01:31 Under suction, the tube collapses and functions as a pressure gauge.

00:01:38 Another indispensable accessory is a water wash bottle.

00:01:42 The classical design is the best, for with it one can dispense a few drops, a fine stream, or a large stream.

00:01:59 The latter technique is useful for filling a graduate to the mark.

00:02:07 A similar wash bottle for methanol or ethanol is an asset.

00:02:14 This style of bottle is particularly useful for wash acetone.

00:02:25 The ether wash bottle has many uses, for example, for rinsing the stopper of a separatory funnel.

00:02:35 Before a crystallization is undertaken, solubility tests should be done in order to select a solvent and to become familiar with the behavior of the substance.

00:02:45 Use a small Pyrex test tube, a few milligrams of sample, and a one centimeter column of solvent.

00:02:55 Rub up the mixture with a rounded stirring rod to see if the substance is soluble in the cold.

00:03:03 If not, see if it dissolves on heating.

00:03:09 More solvent may be required.

00:03:22 When it dissolves, cool the tube and scratch to make sure solid will separate.

00:03:35 Then reheat and let the solution stand undisturbed so that you can judge the quality of the crystals.

00:03:50 This orange substance behaves differently.

00:04:00 It dissolves in cold methanol, but is precipitated on addition of water.

00:04:13 Thus it should crystallize from the solvent pair methanol-water.

00:04:18 Adjust to a point close to saturation at the boiling point and allow crystallization to proceed slowly.

00:04:35 Later, you see that the white compound crystallized well from methanol and the orange one from methanol-water.

00:04:45 With the aid of a creased paper and a spatula, one gram of a white substance is transferred to an Erlenmeyer flask.

00:04:52 It is covered with an amount of solvent judged to be insufficient and the mixture digested on a hot plate.

00:05:01 A paper is folded for gravity filtration of the hot solution, fitted into a stemless funnel, and moistened with solvent to hold it in place.

00:05:18 Additional solvent is added as required.

00:05:22 The mixture is heated and swirled until the solid is all brought into solution.

00:05:42 Then, as a precaution against crystallization in the funnel, some excess solvent is added.

00:05:51 Add a boiling stone to prevent bumping and let the solution reflux to warm the funnel.

00:06:02 Then filter, warm fresh solvent for rinsing.

00:06:23 Pour it in drops onto the top edge of the paper and rotate the funnel so that the whole surface is washed.

00:06:30 The filtrate will be reheated to allow crystallization to proceed slowly, and this can be started at once.

00:06:37 Add a boiling stone and let the hot condensate wash the tip and paper clean.

00:06:53 Now it is ready to stand for slow crystallization.

00:06:57 Do not disturb it, even when crystals start to appear.

00:07:01 Three precautions were taken to prevent premature crystallization, excess solvent, warming of the funnel, and use of a stemless funnel.

00:07:09 Here is a duplicate saturated solution, and you will see what happens if these precautions are all ignored.

00:07:27 Decolorizing carbon is used in purification of a crude solid in case it is not colorless, but has a dull or off color.

00:07:38 This brand of carbon is called norite.

00:07:41 It is so finely divided that one gram has a surface area of 800 square meters.

00:07:47 The active surface adsorbs and removes unsaturated pigmented impurities.

00:07:53 On the right is a simulated dull-colored reaction mixture of a colorless acid and a dye, Martius yellow.

00:08:04 Martius yellow was one of the first synthetic dyes to be used.

00:08:12 It is a direct dye for silk and wool, but does not adhere to cotton.

00:08:23 However, if the crude acid is crystallized without use of norite, the dye largely adheres to the acid to give yellowish crystals.

00:08:33 For clarification with norite, one gram of crude acid is weighed out.

00:08:40 Water is added, and the mixture swirled over a free flame.

00:08:46 Direct heating, permissible when the solvent is water, is the most rapid method.

00:08:51 Be sure to learn and apply the very useful technique of swirling.

00:08:58 The neck of the flask is not too hot for the fingers at the start, but later a spring clip can be used as a holder.

00:09:08 The small amount of dye imparts a strong color to the solution.

00:09:16 Three milliliter portions are to be transferred to four test tubes, each for trial with a different amount of norite.

00:09:25 A capillary dropping tube is calibrated by weighing out exactly one gram of water,

00:09:30 drawing this into the barrel, and marking the one milliliter level with a rubber band.

00:09:50 Draw in and expel hot liquid a few times to warm the tube and prevent crystallization.

00:09:58 Then measure and transfer three one milliliter portions.

00:10:10 Keep the tubes in a bath of hot water.

00:10:15 These capillary tubes contain norite, accurately weighed out on a microbalance.

00:10:23 The ten milligram portion is introduced to one tube by stroking the inverted capillary with a file.

00:10:39 The solution is boiled to mix the adsorbent thoroughly with solute...

00:10:50 and filtered.

00:11:00 The filtrate is colorless.

00:11:02 The five milligram and two and a half milligram samples also absorb the dye completely.

00:11:07 The tiny one and a quarter milligram sample surely reduces the color,

00:11:11 but on careful inspection, the filtrate on the left is seen to have a faint yellow tinge.

00:11:16 Thus, one and a quarter milligrams is not quite enough.

00:11:19 The saturation value indicated of about two milligrams is close to that calculated

00:11:23 for the complete coverage of the surface of the adsorbent by dye molecules.

00:11:29 Although these carbon particles are completely saturated with yellow dye, they are still black.

00:11:36 A second method of clarification shows that heating is only required in working with a hot, saturated solution.

00:11:43 Phthalic acid and martyrish yellow are both acidic,

00:11:47 as is evident from the fact that the solid dissolves in cold water

00:11:50 on addition of one equivalent of potassium hydroxide solution.

00:11:56 A slurry is made by shaking norite with water in a stoppered test tube.

00:12:09 A filter paper is put in place and moistened with water so that it will be sucked down to a tight fit.

00:12:19 And the slurry is poured in.

00:12:30 The filtered water is discarded.

00:12:41 And the yellow solution of sodium salts is then filtered through the thin norite pad.

00:12:46 Although the contact of dye and adsorbent is very brief,

00:12:49 adsorption occurs so very rapidly that the filtrate is colorless.

00:12:56 After acidification, scratching, and chilling, the colorless acid separates.

00:13:11 Isolation of cholesterol from gallstones illustrates further points about crystallization.

00:13:17 These stones removed from the gallbladders of patients of Boston hospitals vary greatly in color, shape, and size.

00:13:26 The large one weighs 79 grams.

00:13:29 Some occur as clusters of small stones.

00:13:32 The color is due to bile pigments, and the main component is cholesterol,

00:13:38 crystals of which are apparent in a fractured stone.

00:13:42 The stones are hard, but easily crushed.

00:13:49 A portion of crushed stones is digested with dioxane on the hot plate.

00:13:54 A free flame must not be used because the solvent is flammable.

00:13:59 The hot plate is faster than a steam bath and nicer to work with.

00:14:03 Washed solvent has been put on to warm.

00:14:06 Swirl well or else the mixture may bump.

00:14:09 When the neck gets hot, use a holder.

00:14:11 A pre-warmed funnel is put in place and the solution is filtered.

00:14:28 Hot solvent for rinsing is sucked into a warm dropper and applied to the walls of the flask.

00:14:56 The filtrate is reheated and water put on to heat.

00:15:04 The hot filtrate is diluted with hot water until nearly saturated.

00:15:26 The yellow color is due to an impurity of a type different from Martius yellow.

00:15:31 This one is not absorbed by norite but is removable

00:15:34 because it stays in the mother liquor when the crystals separate.

00:15:46 Benzoic acid is precipitated from alkaline solution by addition of hydrochloric acid,

00:15:52 conveniently drawn into a pipette by means of a pipetter

00:15:56 made from a surgical syringe, a rubber bulb, and a circle of gooch rubber.

00:16:04 Pour the slurry onto a suction funnel.

00:16:23 Rinse the flask with water.

00:16:34 Eventually a compact cake is produced and suction is at a maximum.

00:16:39 Let it suck until the drip completely stops.

00:16:43 Blow the cake out onto a filter paper.

00:16:46 If you are not sure the stem is clean, as in this case where it was well rinsed with water,

00:16:51 blow against your cupped hand.

00:16:53 The funnel is scraped out and the cake broken up and spread out to dry.

00:16:57 Air drying may take several hours, but vacuum drying is very fast.

00:17:03 Take the tare weight of an Erlenmeyer flask, introduce the moist solid,

00:17:11 connect through a rubber stopper to the suction pump,

00:17:14 and heat the whole flask in the rings of the steam bath.

00:17:17 With good suction, this sample can be dried to constant weight in 15 minutes.

00:17:25 The reaction of this orange compound with aniline to produce a red precipitate

00:17:30 demonstrates that the speed of filtration is dependent upon particle size,

00:17:35 which in turn depends upon temperature of precipitation.

00:17:39 A solution of the compound in cold water gives a fine suspension of reaction product.

00:17:51 An equal portion of orange solid in hot water gives a more granular precipitate of larger particle size.

00:18:09 The finely divided product of cold precipitation partly passes through the paper and filtration is slow.

00:18:21 The hot precipitated material filters much better.

00:18:35 The techniques of filtration demonstrated are applicable without change on a large scale.

00:18:42 On a small scale, the only change is to transfer the hot solution to the filter with a capillary dropper.

00:18:52 That this solution is supersaturated can be seen by addition of a seed crystal.

00:18:57 Purification by crystallization is based on the principle of supersaturation.

00:19:08 Reheated and let cool, the solution is treated with a carborundum boiling stone,

00:19:14 which sometimes functions as a seed.

00:19:23 Spontaneous separation from an undisturbed solution often gives crystals of great beauty.