Cleaning Glassware

232 Cleaning Glassware

rial on the glassware, it needs to be brushed or wiped off before other cleaning processes begin. Similarly, organic solvents are used first to remove grease (i.e., stopcock grease) before water is used to remove salt deposits.

The basic tenet of cleaning is like dissolves like. Polar solutions dissolve polar materials and vice versa for nonpolar solutions. Crystals cannot dissolve in oils, and grease cannot be cleaned by water. Lubricants based on chlorofluorocarbons require chlorofluorocarbon solvents for cleaning. Thus, for effective cleaning, you must know what you are cleaning to have an effective plan of (cleaning) attack.

Borosilicate glassware (such as Pyrex or Kimex) is more chemically resistant than soda-lime glassware. However, hydrofluoric acid, perchloric acid, and all bases can react with borosilicate glass and strip the surface glass off layer by layer. Given enough time, some organic tars and minerals in water can also react with the surface of laboratory glass.

Objectively, the reason we clean glassware is to reuse the glassware. Because some cleaning processes may dissolve glass, you need to be objective about which cleaning process you choose, and on what items to use that cleaning process. Glass dissolving is a cleaning process removing a layer of glass in a process called stripping, and anything that was stuck to the glass is removed along with the glass. Some glass strippers are far more aggressive than others, and they can do considerable damage to glassware in a short time. This damage may include any markings on the glass such as calibration lines. Such destruction may be just a nuisance in an item such as a beaker, but it can also make a volumetric flask absolutely worthless.

Another problem with glass strippers is that they are typically oxide-selective. Glass is composed of a combination of oxides. Because some of these oxides may be more susceptible to specific chemical attack than others, the result is an uneven surface. Such a pitted surface gets dirty easier, and is more difficult to clean, and the greater surface area requires more time for removal of adsorbed gases (i.e., water) in vacuum systems.

It is obvious then that there is no single magic potion that can clean all glassware. Cleaning laboratory ware is an art; and your knowledge of what solvents, or combinations of solvents, to use for any given contaminant will improve with experience.

The best time to clean glassware is just after use. The longer dirty glassaare sits, the harder it is to clean. Fortunately there are often waiting periods in most experiments when things that you are working on are cooling, heating up, or waiting to react. These waiting periods are excellent times to clean glassware. If an experiment has no waiting times, then try to have a large basin with a soapy water solution for used glassware handy (assuming that the contaminants will not react with soapy water). However, be sure the glassware is totally submerged; otherwise, mineral deposits are likely to form on the glassware. Because mineral deposits cannot be removed with soap and water, more complex (and more dangerous) cleaning procedures will need to be used.

One common complication in laboratory cleaning is the proper rinsing of long

source and add a pipette to the hose. By placing a pipette into test tubes, graduated cylinders, or even separatory runnels (which are upside down to provide draining), fast and efficient rinsing can be achieved.

4.1.2 Safety

When cleaning glassware, each item should be handled one item at a time. Although you may be able to hold several items in one hand, it is better to wash one item at a time than to hurry and risk wasting time, equipment, and money (and injury to yourself) which is caused by breakage. There are many ways to clean glassware, but there is only one proper procedure, and that is to do it carefully. Glassware will invariably bounce one time less than the number of times it hits a hard surface. Star cracks (see Fig. 4.3), chipped edges, broken sections, or total destruction are all possible results of the "final landing."

Broken glassware, aside from being a financial loss, is dangerous. Labs often use beakers, funnels, graduated cylinders, and the like with chipped edges or broken ends. This practice is not safe, and many people have assumed that they could not be cut only to regret their naive optimism. Often, by simply fire-polishing the end of a chipped glass apparatus, you can salvage an item that would otherwise be dangerous to use.

Because there are various "strengths" between each cleaner and any other, cleaning glassware can be thought of as a stepwise procedure. That is, as you try to clean something, you go from the least to the most powerful medium until the glassware is as clean as required for the work you are doing. Although it may seem that you would save time to only use the most powerful cleaner, that is not always safe, environmentally sound, or economically wise.

One aspect of cleaning that can save considerable time and energy is remembering that like dissolves like. Polar solvents can dissolve polar contamination far more effectively than can nonpolar solvents. In addition, proper selection of solvent material can avoid damaging the object you want to clean as well as preventing the introduction of possibly hazardous materials. For example, say you have a plastic container with a stick-on label which, after it is removed, leaves a sticky,

Star crack

Fig.4.3 Star cracks are caused by hitting one point of a laboratory flask against a hard surface with enough force to crack the glass, but not hard enough to destroy the flask. The crack lines radiate from the point of impact. They frequently occur in glassware left to roll loose in drawers.

gummy glue. You might try a hydrocarbon solvent to remove the sticky material, but, depending on the solvent, that may to damage the plastic container. However, a light oil, such as WD-40® can dissolve and remove the adhesive.* The remaining oil film can easily be washed off with soap and water.

Regardless of the cleaning process, you should always wear a basic minimum of safety clothing. Lab coats do more than just protect your street clothes; if a dangerous chemical spills on a lab coat, the coat can be easily taken off at a moment's notice with no embarrassment. Street clothes often cannot be removed with equal ease and modesty, and they can provide time for a toxic or dangerous chemical to soak through to your skin.

Eye protection is also critical. Although glasses provide some protection, when liquid splashes, it is seldom considerate enough to aim straight at the glass. Eye goggles fit over glasses and provide protection not only from the front, but from the top, sides, and bottom. If you wear contacts, it is strongly recommended to not wear them in laboratory environments. Although the use of goggles should prevent liquids from splashing your eye, it will not stop vapors. Contact lenses are made from elastomers that are capable of adsorbing vapors, which would then be in constant contact with the eye. Although the use of a fume hood will decrease the danger, it is best to avoid the problem altogether.

Gloves are good protection when using acids or bases for cleaning, and they should also be used with soap and water because they can offer, by removal, immediately dry, clean hands whenever they are needed. They also permit using much hotter water than can be used with bare hands. Typically, the hotter the cleaning solution, the faster and more effective the cleaning. Unfortunately, most gloves cannot be used with hydrocarbon solvents because they are likely to dissolve the gloves. It is difficult to protect hands from the drying effects of hydrocarbon solvents. Although various hand creams are available to remoisturize hands if necessary, it is best to try not to make contact with the solvents.

Never dispose of organic tars, Kimwipes, paper with organic residue, or other solid material down a sink. Such materials should be placed in a waste container labeled for laboratory wastes. Never dispose of used cleaning solutions of any type down a sink without first checking with the safety officer. Different environmental laws exist in each state and sometimes within separate counties, so it is difficult to generalize about waste disposal too broadly.

*In general, as you go from left to right and from bottom to top in the periodic chart, you go toward greater electronegativity. Compounds formed from elements with wildly differing electronegativities are more polar.

*Likewise, one of the pitfalls of walking along a seashore beach is tar blobs sticking to the soles of feet. Again, the selection of a strong hydrocarbon solvent is not advised because such solvents are likely to dry out and/or damage human tissue, and some are carcinogenic. Surprisingly, common baby oil is a wonderful solvent for tar blobs and will not harm the skin.