Notice!

I’ve found that this book project has been showing up on more and more search engines lately and is also being directly linked to for the information it contains(1).  I therefore find it necessary to warn all persons viewing this document that it is a work in progress, and as such it contains errors of all kinds, be them in experimental procedures that may cause harm, or in faulty reasoning that would get you slapped by nearly any chemistry instructor.  Please for now take the information here with a grain of salt.

Most Importantly!

By reading further you agree not to hold the authors of this document responsible for any injuries/fatalities that may occur from attempting to make any of the products or following any of the procedures that are outlined within.  Chemistry inherently possesses a degree of danger and you must understand this, wear gloves and more if the situation calls for it, your safety is in your own hands, not mine!

Also note that this project is open for contribution by any party on the internet.  Simply submit a section to Rob.Vincent@gmail.com and it will be added into the text pending editing and such within a few weeks.  Any person contributing will have their name mentioned in the credits.  Thank you for reading this, and enjoy!

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Although this document may be directly linked to, it will not work in that manner as I have hotlink protection for PDF documents, however directly linking to the html document is possible, still though I would prefer links be to the main book project page.

 

3.0 Lab Techniques (Basic) 

       This section will cover a number of techniques that can be very useful to most chemists.  Refluxing allows for a more complete reaction of reagents by allowing them to react at a temperature very close to or at their boiling points.  Distillation is infinitely useful for the separation of volatile reagents from their non-volatile counterparts, or for driving a reaction where the product can easily boil off.  Filtering is an essential method of removing solid particulate, this comes in handy when dealing with removing solid catalysts from a reaction mixture, insoluble products, or simply some floating pieces of gunk that come in your reagents bought from hardware stores or your products from nearly any reaction.

       Electrolysis is a difficult concept to master but it opens a whole world of possibilities for the manufacture of a number of reagents.  Powerful reducing and oxidizing agents are both possible to make though electrolysis, as the process of electrolysis is itself both a powerful reducing and oxidizing agent.  Covered in three sections including the rarely covered molten salt electrolysis it is the hope of this text just to give the basic overview to the process, nothing more, as such details would take considerable space. 

      Shifting gears again this section goes to titrations which are quite useful.  Usually used for determining the amount of acid or base present in an unknown they can also be used with some modifications to determine the oxidizing or reducing potential of a solution or even its metal content.  Titrations should be preformed with a somewhat expensive piece of equipment called a buret however careful use of a graduated cylinder can give close enough figures for the home chemist.  This section continues with tips on heating and cooling and maintaining temperatures during reactions followed by two methods of purification, removing water from gasses, solids, and liquids along with the ever useful recrystalization.

       This section rounds out with methods of measuring mass and volume and how useful precise measurements are.  All in all these techniques should find use with most chemists who wish to pursue their hobby at home and should hopefully offer a number of alternatives to the professional ways of carrying out these procedures, enough so to allow utilization of these methods in a home environment.

3.1 Refluxing

** Before you ever heat up a reaction, you should try to assure yourself that this will not cause the reaction to get out of hand.  Always start your reactions cold or at room temperature.  If you believe that heat is necessary, heat the reaction after you mix the reagents. **

 

       Refluxing is a common technique, typically used to accelerate reaction rates.  The most common method of refluxing a reaction mixture in a flask is to submerge the flask in oil, water, or a sand bath that is at a constant temperature slightly higher than the boiling point of the solvent.  Attached to the flask should be a reflux condenser (see section 2.1) to cool the gaseous solvent when it rises out of the flask.  The condenser must be long enough and cool enough (a constant flow of cold tap water is usually sufficient) that the gaseous solvent condenses well below the top of the condenser this is usually apparent, a visual vapor line indicating the height of vapor in the column.  This is especially important if long reaction times are necessary, as it will minimize the amount of solvent loss.  Always be aware of the temperature of the bath and try to keep it as constant as possible.  Monitor your reaction closely to be sure that the gaseous solvent never reaches the top of the condenser!

 

       As the reaction flask heats up some of the liquid(s) will volatize and climb into the reflux condenser.  There they intermingle and fall back into the reaction flask.  Then once again they boil off and climb into the column and mingle then fall back in, it’s somewhat similar to simmering in a culinary process to get the flavors to intermingle.  By refluxing for long lengths of time you can react systems with more then one phase or react insoluble solids effectively with liquids or simply speed up a reaction.  The bubbling helping the mixing of the phases and the heat speeding up the reaction. Refluxing is a very helpful and simple technique that is easy to master and should not be looked upon with apprehension.

 

          Note that if you are trying to accelerate the rate of a reaction you should not go from room temperature to refluxing in one step.  The best method is to heat the reaction in increments of 10 to 20 degrees Celsius and see if the reaction occurs at a lower temperature than reflux.  This is much, much safer than immediately refluxing.

 

 

 

 

3.2 Distillation

        Distillation is one of the most essential procedures in all of at home chemistry in my honest opinion.  When it all comes down to it, distillation is about removing a volatile product from a solution, usually for purification and by the same logic, extraction.  The most simple of distillation apparatuses is to the right.

        It consists of four essential parts.  The tube on the left is the distillation flask (this is also known as the reaction vessel), or in this case the test tube.  This leads to a condenser, in this case a glass tube.  The condenser serves the essential role of taking the gasses produced from heating the distillation flask and cooling them down, causing you to end up with a liquid.  In this case the condenser is the most basic design, air cooled, not very efficient, but made more efficient by a fan blowing on it.  Other better condensers utilize running water to cool them or mixtures that can obtain even cooler temperatures.  

        The condenser tube leads into a receiving flask.  This can be cooled as shown in the picture by ice, this is especially necessary if your product that you are distilling over is significantly volatile.  The final part of the setup, the one that really makes it work is your heat source.  A Corning hot plate is about top of the line for an at home lab but basically anything that gets hot and hopefully has a heating control will work. As usual for heating applications borosilicate is preferred.  For a more precise heat control the use of a 'bath' is advised, this is just a beaker full of a fluid (oil in the picture above) that is heated directly, thereby heating your distillation flask more evenly and consistently and if things get out of control, it can act as a heat sink.  The bath temperature is usually about 5-10°C higher then the reaction flask temperature as a rule of thumb.

       Now, heating a liquid mixture to boiling and condensing the vapor may sound easy, but there are several small but important factors that need to be kept in mind.

 

       First of all, the intent of the distillation is to end up with the most volatile compound of your mixture in the receiving flask and the less volatile compound(s) in the distillation flask. No problem you say, because I am condensing the most volatile component. This is, unfortunately, not entirely true. The other components in your distilling flask also have a vapor pressure, which rises with the temperature. As a result the vapor you are condensing mainly consists of the most volatile compound, but it will also contain a fraction of the less volatile compound(s). This fraction will be large if the boiling points of the compounds don't differ much (less than 40°C) and small when the boiling points are quite different.

 

       For example, distilling wine (usually 12,5 vol% of ethanol in water) will yield a solution which is greatly enriched in ethanol content, but it will still contain a considerable (about 50-40%) amount of water.

 

       Secondly, as your distillation proceeds, the concentration of the most volatile compound decreases and the boiling point of your mixture rises (sic). As a result, your vapor will contain more of the lower boiling compound(s) as the distillation proceeds towards completion.

 

       There are several ways to solve this problem, the most important being fractional and azeotropical distillation.

 

       Fractional distillations is actually quite simple, the idea is to redistill your distillate until it's pure. Now, if we take our previous example of wine, about three distillations would be needed to attain reasonably pure ethanol. It goes without saying that this is both time and energy consuming. Being the inventive chaps they are, some chemists came up with a clever solution to this problem: The fractionating column. This simple but nifty device allows you to separate close boiling compounds in one run or in considerable less runs than a simple distillation would require.

 

       The fractionating column is placed between the heated flask and your still head with the thermometer. Vapors which pass through it cool down as they rise and eventually condense, the compound(s) with the highest boiling points condense first against the walls and whatever else is filling your column. As a result there are countless condensation cycles taking place in your column. The condensation of the highest boiling compound(s) delivers condensation heat which evaporates the most volatile compound which is running down the wall. As a result the vapor coming out of the top will almost exclusively contain the most volatile component, unless you are distilling an azeotrope. One could say that inside the column several successive distillations are taking place simultaneously.

 

       There are several types of fractionating columns and they all have their specific uses. The most commonly used column is the Vigreux column (picture?).  It has a relatively small surface area but a high flow rate. The standard 30cm Vigreux column is ideal for separating compounds that have a difference in boiling point of 20°C or more and it can be used for vacuum distillation. Vigreux columns can be made longer or stacked to improve separation, but above a length of one meter one should consider filled columns. Filled columns come in all different sorts and sizes, but they al work on the principle of maximal surface area and therefore they are usually filled with irregularly shaped objects. They retain a lot of liquid and they are also not very well suited for vacuum use. If you are planning to distill compounds with high boiling points or you are using large or long columns you should consider insulating the column to minimize heat loss.

 

       A very important point when performing a fractional distillation is monitoring the temperature, certainly when separating more than two compounds. You’ll notice that the temperature suddenly skyrockets when the most volatile compound is depleted from your mixture because of the good separation of your column. Good measuring of temperature can only be achieved by correct positioning of the thermometer, which should be just below the bend towards the cooler, so that it’s being immersed in the vapor. (PICTURE!!!!!) Slight deviations of a few mm can cause temperature-reading failures of several degrees centigrade.

 

       Azeotropical distillation could be explained as cheating. The trick here is that a third substance is added to your mixture. This then forms an azeotrope, preferably with the compound you do not need to isolate.  An azeotrope is a mixture of two or more substances, which can’t be concentrated anymore by distillation because both components have the same vapor pressure at the azeotropic point.

 

       In this case, the azeotrope needs to have a boiling point that differs substantially from the other component in your mixture. Then you can remove the otherwise hard to separate component azeotropically with the third substance. This process is often used during esterification. Toluene is added to the mixture, which forms an azeotrope with water and boils off. After cooling down the water and toluene separate back into two layers, but this is not always the case.

 

       Azeotropes can also complicate a good separation attempt. A good example is nitric acid. Nitric acid forms an azeotrope with water, which contains 69.2% nitric acid. To concentrate further simple distilling won’t work and neither does fractional distillation. So what now? The most commonly used method is to break the azeotrope by adding another substance. This is completely the opposite of azeotropical distillation where a substance is added to form an azeotrope, so beware of confusion.

 

       In the case of nitric acid, the most applied method is to add sulfuric acid, as this has such a great affinity towards water it will easily “steal” the water from nitric acid. As a result the nitric acid behaves as if it were all by itself in your flask and thus obtains its’ normal boiling point, which is far lower than the hydrated sulfuric acid. One can also snoop the water off by adding a very hygroscopic salt like magnesium nitrate, the only condition being that it does not react with the acid.

 

       The regulation distillation setups used in chemistry labs use ground glassware.  The joints are all tapered glass and fit together snugly, with or without the use of a sealant, which can be anything from silicone gel to concentrated sulfuric acid.  There are two extreme sizes for the professional distillation setup, the 14/20 sets which would be considered the smaller scale, and the 24/40 sets, considerably larger scale.  For example, the largest flask I have seen for a 14/20 set is 250 ml, the largest for a 24/40 is 10 L.  The smaller setup has the advantage of taking up less space and using less of the distillate to wet the vessel therefore resulting in a greater yield, it is great for distilling small amounts but the purification of 3.8 L of over the counter paint thinner may be a pain.  In contrast a 24/40 setup is perfect for this larger project.  But is not good for small amounts, when very small amounts are used the apparatus first needs to be ‘wetted’ with vapor and as such a majority of your liquid might end up lost on the walls of the apparatus and also the larger setup of course takes up a larger space.  It is really up to the chemist and what scale they will be working on to decide.  However the 24/40 joints are more readily available online and elsewhere then 14/20.  But all of this varies country by country, in Belgium for example the most common joint size is 29/32.  Finally in addition to ground glass a time tested method is to use rubber stoppers and glass tubes to connect parts of a distillation apparatus, the drawback being that rubber is attacked by a number of reagents such as oxidizing agents and organic solvents.

 

Picture 1 A 14/20 distilling apparatus the reaction flask being heated in an oil bath.

 

The Metal Distillation Apparatus:

Although the materials section goes to great lengths to show that glass is a great all around material in which to perform reactions there is no reason a metal distillation apparatus should not be considered for some undertakings.  The most notable advantage of a metal apparatus being the high working temperature and the availability of the materials with which to construct one with.  Shown above is a copper condenser in production.  Such an apparatus could be used to distil any of a number of solvents for purification purposes.  It could also be used for inorganic applications such as distilling sodium, something that would be impossible in normal glassware due to the high working conditions. 

Such an apparatus can be simply put together with exoxy and then connected to glassware through rubber stoppers and tubing.  Most chemists will limit themselves to the normal glassware distillation apparatus, but metals are more cost effective and they are more durable.  Definitely a good investment.  Copper is a great choice with which to work, the metal is bendable with the proper tools and it is fairly inert, not to mention most of the connections are readily available as is shown buy the photo above of the distillation apparatus prior to assembly.  However distillation apparatus can be made from other metals as well.

This crude apparatus is a condenser fabricated from steel threaded pipes.  The connection on the right leads from the distillation vessel and connects to the side of it.  The left side actually connects to a jar with the lid attached there to distill into it.  And the copper piping around the vessel cools it, as well as additional piping added to simply hold it in place.  Crude but effective there are many other ways to prepare distillation apparatuses from metals and over the counter items if one is willing to take the time to make one.

 

Here is a quick checklist to follow before performing a distillation:

  1. Check if your compounds form an azeotrope. If not, or if your starting material is below or above the azeotropic concentration, proceed with a normal distillation first. If your compound does form an azeotrope, proceed to step five.
  2. Check the difference in boiling points.
  3. Check the vapor pressure of the higher boiling component at the boiling point of the lower boiling compound. If this is significant and purity is required, use a column.
  4. If you can’t achieve sufficient separation with a column or you don’t have a sufficient column at your disposal, check weather you can use an azeotrope to remove ONE of the components.
  5. If your compounds form an azeotrope, which you want to separate, check if there’s something that’ll form a stronger azeotrope with it or which has a greater affinity for the compound.
  6. Last but not least, check if your components won’t decompose at the necessary temperatures. If yes, carefully read section 8.6 under the advanced techniques on how to work with and distill under vacuum .

       

 

        Distilling HNO3 (Nitric Acid) from a mixture of a nitrate salt and sulfuric acid is a time tested way to isolate this useful oxidizing acid.  So an adventurous chemist combined an unweighed quantity of NaNO3 (sodium nitrate) into a flask with a large quantity of 94% H2SO4 (sulfuric acid) and attached a condenser though which water was run and in turn this ran to a receiving flask.  Some boiling stones were also added (pieces of obsidian) to help ease the boiling process and make it smoother.  However complications where run into shortly after heat was applied, the black boiling stones started to color the mixture black, and the gas running into the condenser was a dark red, not what would be expected for a clear to off yellow acid.  Regardless distillation was continued and in the end the chemist ended up with 20 ml of a dark red volatile distillate.  Upon addition to water it decolorized and left an acid solution.  Although not obviously apparent to the chemist at the time they had distilled NO2, a highly toxic gas that is one of the decomposition products of nitric acid.  Their ambitiousness and inexperience resulted in them heating the reaction mixture too high and the concentration of their acid only would have allowed 95%+ HNO3 to make it over, which would have called for a vacuum because high concentration HNO3 decomposes somewhat more readily then the more common 70% grade.  The chemist eventually realized their mistake by simply observing the physical properties of the product ran in contrast to those of the desired product they thought they had.  Luckily the chemist made it out unscathed.

 

Important Safety Concepts:

Heating:

       When distilling one should use a safe method of heating, which prevents your glass from cracking and improves its life. It also protects you from a bursting apparatus, which showers you in dangerous chemicals. If heating with a flame try to keep away from that section of your apparatus.

 

Flames:

       Open flames are NOT a safe way of heating. Flames cause localized overheating and are especially a hazard when distilling flammable substances.  Flames that are non-diffuse such as flames from a torch can cause extreme stress and failure of glassware, either use flames to heat a bath that your reaction vessel is in, or use a very diffuse flame.

 

Electric Heating:

       Electric heating mantles or hotplates can be used with certain exceptions. Under normal pressure one can safely use a hotplate (preferably with magnetic stirring) to heat an Erlenmeyer. However, one should be careful with flammable substances. If the temperature of the hotplate surface is higher than the auto ignition point of your substance, it cannot be used unless the whole apparatus is sealed to the entry of atmospheric oxygen and the output gasses are property taken care of. Same goes for electric heating mantles. Heating mantles should be used for flasks because a hotplate causes localized overheating with its flat surface! Note that heating mantles usually impair magnetic stirring, unless you buy a magnetic stirrer which fits the heating mantle, but these are usually within the >500$ range.

 

Baths:

       Baths are ideal for heating flammable substances, certainly water baths. Water has the advantage of being not flammable and it’s high heat capacity can be beneficial when distilling. However, water evaporates rapidly when used above 80C. Oil baths don’t evaporate as quick as water, but they have other disadvantages. Most commonly available oils smell and are flammable. They also pose a severe explosion hazard when distilling oxidizing material. Ideal are silicone baths or other non flammable synthetic oils, but these are usually hard to get and/or expensive.  For lower temperature applications or if you just don’t care about your hot plate a sand bath can be used by simply filling a pan with sand and putting on your plate, but at higher temperatures the insulating effect of the sand can burn out the heating element in a hot plate so be warned.

 

SealingJoints:
       Sealing your joints is very important. Improperly sealed joints will cause losses but they also pose a safety hazard, because they allow air to enter. This is mainly dangerous when distilling flammable substances or when distilling under vacuum. Joints are commonly sealed with grease. There are several types of grease and they all have their disadvantages. Vaseline is cheap to get and easy to use, but it’s chemical resistance is limited and it will contaminate organic solvents. Other options include silicon oil, but this is expensive and does not provide 100% chemical resistance either, and specialty high vacuum greases composed of higher fluorinated hydrocarbons but they can cost a bundle. Therefore the author recommends cheap, white, teflon tape available from any hardware store to seal pipe joints. This easily fits between the joints and has excellent chemical resistance. Wrap one layer around the ground glass male side and press into the opening opposite, giving a slight twist, do not force or twist too much though or you might crack or otherwise damage your glassware.

 

        This is a common procedure for the inorganic chemist, less so for the organic chemist but none the less important.  Evaporating to dryness is a feasible method of recovery of a pure product providing:

1.      Your intended product will not decompose at the temperatures necessary to volatize the solvent. [Note: Vacuum can decrease the necessary temperature to remove the solvent and prevent decomposition of your product]

2.      Any other compounds in your solution besides your intended product are also volatile.

3.      Your intended product will not volatize to any major degree at the temperatures used.

4.      Your intended product will not explode at the temperatures used/is not pyrophoric at these temperatures.

5.      An extremely pure product is not required/additional purification will take place.

        Examples of simple procedures would be:

·         Making AgNO3 by dissolving silver in HNO3 and boiling off the HNO3/Water.

·         Neutralizing BaCO3 with HCl then boiling off the water and HCl.

Examples of procedures that will not work are:

·         Boiling off the water from commercial bleach (NaOCl decomposes, NaCl/NaOH impurities)

·         Dissolving Na in MeOH then boiling off the alcohol (NaOMe decomposes)

·         Dissolving Al in HCl then boiling off the HCl solution (AlCl3*xH2O decomposes to oxychlorides)

        Things to watch out for consist of azeotrope distillation when involving liquids and carry over of less volatile insolubles.  Additionally when a solution has nearly evaporated there may be a heavy precipitate on the bottom, this can cause 'bumping' in the flask which can bounce a flask off a hot plate or even crack it due to the pressure of the vapors rising though the precipitate.  To avoid the worst of this you can cool the solution when a precipitate starts to form then filter it then resume heating, or resort to magnetic stirring, or heat at a lower temperature then the boiling point of the liquid.  When creating a salt by reacting an acid with a metal/carbonate/hydroxide etc. be sure to use the stoichiometric quantity of acid if at all possible, excess acid will only have to boiled off resulting in noxious clouds that kill grass, other plants, your eyes, and lungs (this is assuming the acid is volatile, e.g. H2SO4 will not be easily volatile).

·        Sublimation

Sublimation is usually considered the process by which a solid can go to the gas phase without passing through the normal intermediate liquid stage.  A number of substances are known to sublime, common substances include naphthalene, paradichlorobenzene and the most famous of all, iodine.  However many substances can and do sublime even if a liquid phase does exist.  The main thing to consider is a vapor pressure.  All substances theoretically have a vapor pressure, even high melting solids.  Normally a substance has a higher vapor pressure the closer it is to the melting point and from there the closer it is to the boiling point.  But many substances, especially organics have vapor pressures that are appreciable at room temperature.  If the vapor pressure of a substance can be increased, by applying vacuum or by heating, or both then there is a better chance of subliming the product.

Sublimation can be considered a form of short path distillation and can be done providing two criteria are met.  1)  The substance to be sublimed must have a high vapor pressure.  2)  The substance from which the product is to be sublimed must have a relatively low vapor pressure.  Sublimation at room temperature is usually slow, but as stated above, applying vacuum and heating increase the vapor pressure of substances and allow more of the molecules to escape in the gas phase and therefore allow more of them to recondense on the conveniently placed cooler areas of a vessel.  The picture shown here is just one way to setup a sublimation apparatus using an Erlenmeyer flask with a side arm to which vacuum is applied.  The crystals cooling on the test tube inserted into the rubber stopper and full of ice.  When the sublimation is complete the stopper is removed and the crystals are scraped off.  Other simpler apparatuses, can easily be improvised just knowing the normal parts of sublimation, basically you need a partially enclosed environment, a cooler part of a vessel, and a warmer part (a simple example being a jar with a bowl sitting in the opening full of ice, with mild heat applied to the bottom).  But even at room temperature sublimation will occur as stated, in which case crystals will usually sublime to the top of a test tube. 

       Sublimation is great for substances with high freezing points which could otherwise allow the substance to solidify in distillation apparatus and possibly clog it during operation.  It is also great for substances that might decompose at higher temperature or have prohibitively high boiling points (some substances with high boiling points can sublime at considerably lower temperatures).  Usually not a procedure for the large scale, sublimation does offer yet another tool with which a chemist can retrieve a product from a reaction mixture or a reagent from an over the counter product. 

3.3 Filtering 

       So, you have a mixture of a liquid and a solid that you want to separate.  Filtration is the answer.  It’s easy, fast, and effective.  The only things you really need are a funnel and a piece of filter paper (a coffee filter will work too, or even a wad of cotton). To determine which type of filtration is best, you need to know whether you want to keep the solid or the liquid.  There are three common types of funnels that are useful to a chemist: liquids, powder, Buckner.  A liquid funnel has a long, narrow spout and is usually best for simple filtrations, using a cotton wad or a properly folded filter paper or coffee filter.  However because the spout and subsequent area that drains into the spout is so small it is only good for filtering a tiny amount of precipitate otherwise it may become too packed to filter, even with vacuum filtration.  Powder funnels have a much wider spout and are useful for filtering things that might clog a smaller spout funnel.  Buckner funnels are the best for isolating solids, but they work best with a vacuum (more on that below).

       You may be wondering, what good is filtration anyways?  I can always decant my mixture can’t I?  Well, yes you can, but there are some inherent problems associated with decanting.  1)  If the solid material left at the bottom of your flask was your goal, what you have left will contain appreciable reaction mixture, and some of your solid will probably be lost during the actual decanting process.  Or 2) If the liquid is your goal appreciable liquid will be left in your solid that could otherwise be obtained by filtration, and also small particulate may come over during the actual decanting process ruining the purity of your new reagent or the solid may not totally settle out.  Filtration is almost always preferable to decanting.  Also before selecting a filtering method one should consider a few things:

1.      What quantity of liquid will I have to filter?

       Number one is important because gravity filtration is not a good method to filter large quantities of liquid, both due to the time involved and the possibility of clogging of filter paper, in this case vacuum filtration is more appealing.

2.      Am I trying to recover my liquid component?

       If you are trying to recover your liquid component and not your solid component, sand or diatomaceous earth could be put onto the filter paper to increase the efficiency of the filtration and speed it up.

3.      Am I trying to recover my solid component?

       If the solid component is your goal then special care should be taken to make sure your solid is recoverable in high quantity from the filtration method of your choice.

4.      Do I think the crystals, both in volume and by their size might clog my filter paper?

       The possibility of crystal masses clogging filter paper is exceptionally high in the case of really fine precipitates, which can cause a complete stop to filtration, in addition large quantities of crystals can do the same or overflow my filtration method. 

5.      Do I have fine particulates that might pass though filter paper?

       If there are ultra fine particulates in the filtrate there are very fine filters that could be used to remove them.  Letting the solution rest for a few days can ‘age’ the precipitate resulting in a more manageable solution or filtering though sand or diatomaceous earth or even a fine sintered glass filter can remove many fine particles.

6.      Do I have to filter it while hot?

       If you have to filter a solution when hot the first addition of the solution to the filter paper can result in crystallization on the filter paper resulting in almost no filtration ability, which can be catastrophic in some situations where a very hot solution is teetering around.  Pre-washing the filter paper with hot solvent or heating the glass/porcelain parts of the apparatus in an oven can help here.

7.      Does my substance to be filtered contain components that may not take nicely to filter paper?

       Finally, my last point to consider, how will the actual substance passing though the filter paper affect it?  Most of the time it won’t affect it greatly, but some copper complexes can attack cellulose, as can strong sodium hydroxide solutions or strong oxidizing solutions like concentrated nitric acid, passing these though a normal filter paper could spell doom for the reaction and will at the least call for you to filter again, for oxidizing agents try filtering with glass wool(1).

       So how do I filter my substance?  Well that depends on what type of filtration you want to take advantage of (see below).  But the normal procedure is to slowly decant your liquid into the funnel without adding the solid at the bottom.  In this way the filtration can proceed smoothly, because the solid particles will slow it greatly.  The liquid mix is added in small increments to your filtration method, if you are taking advantage of the insolubility of a salt yields may be increased by cooling the mixture until it is near the freezing point to depress the solubility.  After each addition you should wait until the addition is nearly though the filter paper.  Then add more, keeping up the process till all of your solution is used.  Once only a small amount of liquid is left in your beaker swirl around the liquid and dump it in all at once to get your solid onto the filter paper. 

       When all of your liquid has been added the, solid left in the filter paper is washed with cold solvent (whatever your solution is) is added to the flask you were filtering from and swirled around to remove any solid left and this is added to the filter cake to wash it and add this extra little bit of solid to the batch.  The cake can then be washed with additional aliquots of solvent.  After your solid is thoroughly washed it can be removed from the filtration apparatus and spread out on filter paper or in watch glasses to dry.  The basic components of a filtration system are a membrane to separate the filtrate from the non-filtered solution, and a place for each to go.  There is room for emergency improvisation here, the author of this text has for instance seen a beaker with a coffee filter over it held in pace with a rubber band inverted over a collection vessel and heated externally with a torch, the increasing vapor pressure in the flask forcing the liquid though the filter.  Although this is not a recommended method it just goes to show filtration is a mechanical process and can easily be modified to be accessible in your situation.

(1)

In the case of filtering oxidizing solutions you can give glass wool a try, or alternatively fiberglass insulation, this should first be cleaned by stirring with hydrochloric acid and drying, if your product however looks bad you may want to find a different source for your glass wool substitute.

3.3a Selection of filter paper 

       First and foremost: size.  The filter paper you use must fit your funnel or bad things will happen.  The filter paper should fit entirely within the sides of the funnel.  For a Buchner funnel, the filter paper should cover all of the holes on the flat portion, but the edges of the filter paper should not touch the vertical sides of the funnel (it won’t seal under vacuum otherwise).  If you don’t want to buy all kinds of different sizes of filter paper, remember that a big piece can become a small piece, but not vice versa.

The type of filter paper you use really depends on the size of the solid material you are filtering away.  For most applications coffee filters are sufficient, but coffee filters are relatively thin and can’t take much abuse.  If you can get real filter paper, do it (The stuff from Whatman is the best, and not all that expensive).  For larger crystals a wad of cotton packed into a liquid funnel works very well.  If you have a Buchner funnel, you need a flat piece of filter paper so coffee filters are no good unless you cut them up to fit your Buchner.  For filtration of very fine particles, like charcoal dust, you can find very high efficiency filter paper, but the cost is rather high.  If you really need it, the best stuff is made from Teflon (a slightly cheaper alternative is a nylon filter paper but this is still quite expensive and a special commodity) and can be found through chemical suppliers or chromatography suppliers.  Using Teflon filter paper requires vacuum filtration.  You can sometimes sidestep the need for Teflon filters by using a “filter aid” such as diatomaceous earth, sold by the trade name “Celite.”  Celite is essentially very, very fine dirt, but it really works well!  (See the vacuum filtration section for details on its use).  As a final note, all filter paper, no matter how expensive, is really only good for one use.  It’s not worth ruining an experiment to save a few cents by reusing a piece of filter paper.

3.3b Gravity Filtration 

       Gravity filtration is slower than vacuum filtration, but requires less equipment and is generally more effective.  Gravity filtration is better for isolating the liquid phase than the solid phase, but if you don’t have a vacuum, it will still work reasonably well for isolating the solids.  To perform a gravity filtration, you need a funnel (liquid funnel is best, but a powder funnel is okay too so long as you use filter paper and not cotton), filter paper, and a flask to collect the liquid.  There are many ways to fold a flat piece of filter paper in to a cone shape.  The best way is called “fluting” and consists of folds in opposite directions along the diameter of the filter paper (FIGURE).  A simpler, although somewhat less effective method, is to fold the circle in half and then fold the semi-circle in half again.  This wedge can be opened to form a cone, such that half of the cone has a one-ply layer of paper and the other half has a 3-ply layer.  Fluting the filter paper will give a significantly faster flow rate!  Fold the filter paper whichever way you choose and then place it inside the funnel.  Clamp your receiving flask in place (important!) and then set the funnel on top.  Slowly pour the mixture into the filter paper cone.  The liquid level should never be higher than the top edge of the filter paper or the mixture will spill over and go through unfiltered. 

       Gravity filtration is relatively slow (remember, fluted filter paper has a faster flow rate, it’s worth the extra folds!) so just add enough of your mixture to get close to the top and then let all of the liquid flow through before adding more.  This may seem unnecessarily slow, but if you slip and add too much of the mixture and some gets through unfiltered, you’re just going to have to start over again.  Once you’ve poured in all of your mixture, rinse your reaction vessel with the solvent and then rinse the solids thoroughly.  Let the solvent drain completely before adding more to rinse.  If the solids are slightly soluble in the solvent, be sure to use ice cold solvent and try to use as little as possible.  Gravity filtration cannot be used reliably for solids that precipitate as ‘gels’ such as iron or aluminum hydroxide, these are very difficult to remove water from and easily clog filter papers if not assisted by vacuum.  Also note that filtering organic liquids of low density or just in general through filter paper can prove difficult without vacuum as their low density gives little incentive to pull them through the filter paper and in addition filter paper contains water as papers are hydrophilic and as such they can ‘intimidate’ organic liquids from readily passing through them.

3.3c Vacuum Filtration 

Filtration using a hand vacuum pump and a Buckner Funnel in a Erlenmeyer Flask with Side arm.

 

       Vacuum filtration is the fastest way to filter a mixture, but it’s not always the most effective.  If you want to isolate the solid material, this is the best way to go.  You will need a Buckner funnel, a piece of filter paper, a rubber sleeve for the funnel, an Erlenmeyer flask with a vacuum sidearm, and a vacuum pump.  First, put the rubber sleeve around the spout of the Buchner funnel.  The sleeve should fit snuggly and be larger than the opening at the top of the Erlenmeyer (we want it air-tight, remember).  Clamp your Erlenmeyer in place (important!) and then set the Funnel on top of the Erlenmeyer and drop in the filter paper.  Wet the filter paper with a little bit of the solvent from your reaction (this will help the vacuum seal).  Connect the hose from your vacuum to the tubing adapter on the Erlenmeyer.  Turn on the vacuum and then slowly pour the mixture onto the filter paper.  The solvent should be sucked through quickly.  Try to keep the filter paper moist since it won’t seal when it’s dry and the solid can be sucked through around the edges of the paper.  Once all your mixture has been poured onto the filter rinse your reaction vessel with solvent a couple of times and then rinse the solid a few times with a little solvent (if the solid is slightly soluble in the solvent, be sure to use ice cold solvent and try to use as little as possible).  Pull air through the solid for a minute to dry the solid.  Then turn off the vacuum and you’re all set.

 

For filtration with Celite, set up the filtration apparatus as described above, then add an even layer of Celite 2-3 cm thick over the top of the filter paper.  Turn on the vacuum for a few seconds; the layer of Celite should compress a little.  Wet the Celite with solvent and then turn the vacuum on again briefly.  Repeat the process of adding a little solvent to keep the Celite wet and then turning on the vacuum to pack it down.  This process is essential to separating very fine dust from your mixture.  When you are satisfied with the packing of the Celite, turn on the vacuum and slowly pour your mixture onto the filter.  Try not to disturb the Celite too much, you want it to stay as even as possible.  Next rinse the reaction vessel and the Celite.  I repeat, rinse the Celite.  A lot.  There is a lot more to rinse than in a regular filtration.  My favorite method for this is to turn off the vacuum, add a volume of solvent that is roughly the same as the volume of Celite (the solvent shouldn’t go through the Celite filter with the vacuum off) and then suck it through by turning on the vacuum.  I usually repeat this process 2 or 3 times.  Finally, if you are using Celite as a filter aid, it is all but impossible to recover your solid material, so be aware!

3.4 Electrolysis 

              An amateur chemist can easily define electrolysis as any reaction that calls for the direct application of an electric current to a chemical, either on its own, or in solution, for purposes other then heating.  Our point here is to understand how we can transform chemicals using electricity. The key word is “ions”. What is an ion? A quick and dirty definition would be: “It’s an electrically charged atom or molecule”. The positively charged are called “cations” and the negatively charged are called “anions”. Ions have different chemical and physical properties than the original atom or molecule. All anions have their own name, so Br- is baptized Bromide and NO3- is Nitrate. Cations with more than one possible charge also have names, so Cu+ has one electrons missing and it’s baptized Cuprous, Cu++ has lost two of them and becomes Cupric. [See table in section 1.3 for a list of common cations and anions]

        Many chemicals, including all salts, are made of opposite charged ions “glued” together by electrical forces. And in these ‘ionic compounds’ electrolysis can help unglue them.  There are basically three schools of electrolysis that you should familiarize yourself with.

Pure Compound / Molten Salt Electrolysis

This is the simplest form of electrolysis.  Not in its practice, but in concept.  A pure compound. ionic in nature, i.e., consisting of a cation and anion, is heated until it becomes liquid.  Ionic liquids are good conductors of electricity and therefore are able to be electrolyzed directly.  Once molten, electricity is applied and the compound breaks down into its constituent parts.  For example, molten sodium chloride when subjected to DC electrolysis will break down into liquid sodium metal and chlorine gas.

Aqueous Electrolysis

The most common form of electrolysis for the at home chemist.  An ionic salt is dissolved in water and a current applied.  Depending on the reduction and oxidation potentials of your cations and anions you get different products.  For example, electrolysis of water, with a little salt added to aid in conductivity will yield hydrogen and oxygen gas, excess salt and a higher current will yield hydrogen and chlorine gas.

Non-Aqueous Electrolysis

A compound is dissolved in any liquid other then water and current applied.  Different products are possible under different conditions.  Products are possible with non-aqueous electrolysis that are impossible in aqueous electrolysis or would require high temperatures for molten salt electrolysis.  For example, it is possible to obtain lithium metal as a deposit in the electrolysis of lithium chloride in pyridine, whereas lithium metal would react instantly in water and molten salt electrolysis would require temperatures of several hundred degrees Celsius.

       There are two different types of electricity available.  There is alternating current (AC) and direct current (DC).  Alternating current is the type of electricity that comes out of the wall, this is not good for electrolysis, alternating current changes which side of your cell is your cathode and which is your anode about 60 times a second, this means that almost nothing can be accomplished with it(1).  If you have a cell full of water and something to make it conductive and put two electrodes into it, plugging it into the wall the only thing you will do is heat your solution to boiling with resistance heating, make a random explosive gas mixture above your water, and deform your electrodes.  Therefore your only real choice for productive electrolysis is DC.

        So where does DC come from? I will not detail the electronics here. There is plenty of information elsewhere on the internet.  But you usually have two sources, converting the output of your wall adaptor to DC, or using batteries.

 

·        Batteries: Not very useful, except for simple demonstrations. Those little square 9V batteries make me laugh! If you insist on using batteries, be a man, use 4 “C” size (big) batteries or a lantern battery or even a car battery, but if you go with the car battery then you’ll need a charger, and you could just use that directly anyways.

·        Adapters: These are very common these days and most households have one or two spare ones from old equipments that broke. 6 to 9 volts is fine for most experiments and they usually deliver above 0.5A. Another common source of power that falls into this category packing a little more punch is the car battery charger.  A good one can supply from 0 – 12 V and from 0 – 55 A, and can be procured cheaply from second-hand stores.  Old ATX power supplies from computers are marvellous for electrolysis because they yield high amperages (up to 20A) at low voltages (5 and 12V).

·        Build your own simple power supply: If you have some skills on electronics, you can built your own power supply just using a transformer and a single 1N4001 diode.

 

Build your own variable power supply: An extra potentiometer (100Kohms) and a power transistor like  TIP 31 (3A, 40W),  TIP 41 (6A, 60W)or TIP3055 (15A, 90W; a.k.a. 2N3055), can give you control over the voltage supplied by the batteries, the adapters or your home built power supply. Don’t expect precision or stability though:

 

A power source capable of delivering at least 0.5 ampere would be nice. The product yield per hour depends on the current, so your current should be proportional to your hurry and your electrode surface area (too much current per square centimeter may cause unwanted results).

The electrolysis process is sensitive to the voltage applied, but if you want a “rule of thumb” number, 9V will perform most tricks. 

An exercise in calculating yields involving electrolysis.

Let’s say that you want to make bromine, and just to simplify things let’s say you have some lead (II) bromide laying around to perform molten salt electrolysis on.

First off you divide your reactions into half reactions, the half reactions, when added together cancel out but separately they give the number of electrons necessary and help in visualization.

Pb2+ + 2e-  Ž  Pb(l)

2Br- Ž Br2(g) + 2e-

Notice how the number of electrons on one side of the equation match the number of electrons on the other side of the other equation.  That is because while one thing is reduced (gains electrons) another thing must be oxidized (loses electrons) a good way to remember this is the mnemonic OILRIG [Oxidation Involves Loss, Oxidation Involves Gain (of electrons)].  Couple this with the mnemonic RedCat [Reduction occurs at the cathode] and you can figure out where your products will be produced at.  When wires are color coated in their normal manner the cathode is the black wire, the negative (-) wire.  By default then the red wire is the positive (+) wire, is the anode.

Now that you know your reaction, what kind of power source are you using?  Maybe you’re using a simple wall adaptor, possibly from a phone charger and the phone broke.  Looking on the plastic you might even find that it is 6.2 V and .5 A.  That’s all the information you need off that.  The next step is to calculate the number of coulombs ( C ) of electricity that pass though the molten mass.  A coulomb is a unit of measurement specific to things involving electricity, it is equal to one amp times one second.  So it actually measure the quantity of charge moving though the cell.  So let’s say that we are going to run this for 30 minutes:

.5A . .5h . (3600s/1h) . (1C/1A.s) = 900 C

To explain the above equation you can see the that .5A came from the power of the power supply, the .5 hours came from the time the cell was running, the other numbers are conversions to the number of seconds in an our and the number of amp-seconds in a coulomb.  This is the generic representation and you can just plug in your numbers in the above equation to get your own unique answers.  Now we see from the two equations way overhead that for every one mol of Br2 generated  two mols of electrons are simultaneously brought into existence.  Now we need a new unit of measurement for electrolysis, a Faraday (F).  A Faraday is the number of electrons necessary to reduce one mol of a single charge unit.  A Faraday is equal to 96,500 C.  From here we use a new equation:

g. Br2 = 900 C . (1 F / 96,500 C) . (1 Mol Br2 / 2F) . (159.8 g Br2 / 1 Mol Br2) = 1.5 g Br2

In the above equation we took the number of coulombs that we got from the first equation and multiplied it by the conversion for Faradays to coulombs and that by the mols of Br2 and the number of Faradays involved, e.g., in this case two mols of electrons are involved and therefore there are 2 F.  This is all multiplied by the grams of Br2 per mol to give 1.5 g of Br2 produced overall.  To get lead you could convert the grams of Br2 produced and make it into mols, then you could multiply that by the grams per mol of lead or just substitute that information into the last part of the above equation.

Well, most of you are thinking, “Only 1.5 g…. what the heck, I wanted a liter!” Well, this is not the setup you would use for massive Br2 production.  But electrolysis is good for producing small quantities of hard to obtain chemicals, and you could increase your yields by either increasing the amps of your power supply or by running the setup longer.

 

 

       Aside from a power supply the second most important consideration are the electrodes.  Many of the metals are similarly conductive for all intents and purposes and therefore it is better to consider them in terms of their chemical resistance relating directly to whatever environment you are planning to perform electrolysis in and the ease of procurement of the electrode material.

 

·        Copper can be easily obtained from common wires. Copper has a wide resistance to many environments.

·        Zinc can be found as the outer metallic shell of common batteries (the cheap ones, called carbon-zinc). Not good for acidic environments or basic environments.

·        Carbon or graphite: These are very useful electrodes, since they do not oxidize as anodes. Well, they don’t last forever; they are attacked by oxygen, originating CO2, or maybe just disaggregate in the solution, but are much, much, cheaper than platinum electrodes, so they are widely used. The most common are pencil’s graphite. These have very different compositions, and may or may not last long. In fact, they may even be very bad conductors. Another source of carbon electrodes is the carbon rod that every carbon-zinc battery has inside. They are better than pencil’s graphite. The best carbon electrode I found is a rod of graphite covered with a copper layer found in solder’s supply shop. When you strip the copper with ferric chloride (or electrolysis), a resistant graphite electrode is left. Another option is graphite from electric motors sliding contacts. They are small, but easy to find and quite resistant. I have a couple from large polisher that are 23x16x6 mm.

·        Lead is used often as an inert electrode. You will probably find it in a sporting goods shop: fishing weights, gunshots in general, airgun bullets etc(3). It melts easy and you can cast your electrodes melting it with a blowtorch and a scoop.

·        Nickel: Coins from some countries contain an appreciable amounts of nickel(2) and can be used as electrodes, additionally nickel can be procured from scrap yards or specifically for electrolysis.  Nickel is an excellent material for electrolysis of highly basic solutions.

·        Iron:  Iron is attacked readily under acidic conditions and somewhat slower under basic, but it is commonly available and may find some use in a pinch.

·        Platinum: If you have the money, it’s the most resistant anode I know. Fine wire is ok, but for larger surfaces, other metals plated with platinum can be used.

·        Silver/Gold:  A cheaper alternative to platinum somewhat more reactive.  Available from coin suppliers in the form of collectable currency either can be melted and cast into the appreciable shapes desired.  Silver wire can be purchased from jewelers as can platinum.

·        Misc. Electrodes:  Mercury(4), lead dioxide(5), rare earth oxides plated on titanium, tantalum, there are hundreds of possible electrodes that one may come across that are not covered here.

 

(1)

AC electrolysis is really a good way to fry electrodes.  Nothing will survive AC electrolysis of hydrochloric acid, even platinum will succumb to this, which is a good way to prepare soluble platinum compounds ironically.  Even carbon will be destroyed.

(2)

Older American nickels contain decent amounts of nickel but older Canadian coins contain an even higher amount.  The amount of nickel in coins in your country can usually be found easily by searching online.

(3)

Lately there has been a push in some areas to replace these lead items with the more environmentally friendly bismuth, at this time though products that have been replaced with bismuth usually proudly proclaim it as being environmentally friendly so determining what you have is still relatively easy, lead in these items is also usually alloyed to a small percent with other elements such as antimony.

(4)

Mercury electrodes are famous in the mercury cathode cell for the preparation of sodium hydroxide.  In this cell the mercury electrode forces the reduction of sodium cations to sodium metal rather then the production of hydrogen, the result is a mercury-sodium amalgam, containing a few percent sodium metal, this reacts with water slow enough to allow recovery of it, to look further at this phenomenon search ‘over voltage’ online.

(5)

Lead dioxide electrodes must be formed carefully, they have their claim to fame in the preparation of perchlorates by electrolysis of chlorates by the armature chemist.

3.4a Molten Salt Electrolysis

       Performing electrolysis on a molten binary salt usually yields predictable products providing you have a simple anion coupled to your metal ion.  Another advantage is that electrochemistry can produce many elements that would not be possible to produce under aqueous conditions.  The most common examples including producing the alkali and alkali earths electrochemically.  Of course the most prohibitive feature of molten salt electrolysis is the high temperatures usually employed.  The corrosiveness of molten salts and some of the products produced by the electrolysis, especially at the temperatures employed these factors usually result in molten salt electrolysis being beyond the reach of the beginning chemist.  However, many chemists would like to do molten salt electrolysis, and they can, the procedures outlined within this section will cover the basic points for this method of electrochemical production.

Working with Molten Salts

          Great care must be exercised when working with molten salts.  For the most part this is due to their high melting points.  Think about what happens when drop of water hits hot grease, the spattering and violence of the sudden evaporation of the water, now consider molten salts can be several hundred degrees Celsius hotter.  Water hits these salts like a bullet, sending liquid everywhere.  Due to the temperatures it can greatly dehydrate anything organic and it can also start fires on wood and paper and such.  It should also be noted that molten ionic salts are good solvents for…. Whatever, they attack a multitude of things and some they flat out destroy.  Specific examples like molten sodium hydroxide (above) destroy wood and such on their own, let alone at high temperatures, getting a quantity of this on your skin would be disastrous.  When working with molten salts your apparatus should be firmly placed on a flat surface, and once the salt is molten it should not be moved and you should limit how much you ‘mess with it’ as many mistakes can occur.  Wear welding gloves that can easily be removed if you get your salt on them and avoid inhaling the fumes coming off the melt too much, they can cause sickness and throat pain and loss of vision (as I once experienced).  Finally, when you are done with a reaction, allow the salt to cool to room teperature on its own, in case of emergency the salt can usually be dumped in sand.

       Nearly everything in your electrolysis cell will have to be metal due to the temperatures employed, although less used, ceramics may also be employed for some applications.  Some lower temperature cells may safely employ Teflon (not for use with molten alkali’s) or even some epoxies or cements.  The type of cell construction depends entirely upon the types of products produced.  The physical state of the products and their inherent reactivity after genesis is of the utmost importance and of equal related importance is weather the products thus formed will react with each other or even with the melt.  So here is your quick checklist:

1.      What is the best melt, and eutectic composition or a straight composition and at what temperature does it run?

2.      What products will be formed through electrolysis, if an eutectic mixture, will only one product be formed at the anode and one at the cathode?  Are you sure of both your anode and cathode products (check their potentials against charts(1)).

3.      At the temperature employed, what will be the physical state of the products formed?

4.      If the products are solid then they will not mingle, however if they are either liquid or gas, will they react back with each other and thus make it necessary to divide the cell or otherwise separate the products from one another?