UNIVERSITY of DELAWARE
DEPARTMENT of CHEMISTRY and BIOCHEMISTRY
|Glassware Care & Cleaning|
It is very important that glassware is used and stored properly to prevent failure or injury. Any scratches, whether noticeable or not, greatly reduces its strength. Whenever possible, do not let glass apparatus contact metal, grit or even other glassware. Plastic stirring rods and scrapers should be used to prevent scratches and prolong glassware life. Glass should not be scribed or etched. This is especially important when it is to be used for pressure or vacuum work.
Chemistry Student approached the Master and asked, “Master, how
do I achieve enlightenment in Chemistry?"
The Master replied, “Wash your glassware.”
Clean glassware is essential in chemistry. The problem is that the tolerance for shmutz varies with the work you are doing, and sometimes a chemist does not know how important clean glassware is to an experiment until it has failed. This document is designed to give an undergraduate chemistry student a brief introduction to what chemists mean by "clean" and how it can be achieved.
are two broad degrees of clean in chemistry; quantitative and normal.
Quantitatively clean glassware is required for the most demanding
applications where a quantity is being measured at high precision,
such in analytical or physical chemistry. Glassware at this level
of cleanliness has no residues (e. g., grease) or other impurities
on it. Normal clean glassware is free of large amounts of impurities,
but some grease may be tolerated. Glassware that has been cleaned
normally is used where high degrees of precision are not required,
such as in a synthesis.
General Cleaning Tips
The key to cleaning is doing it a timely manner; letting dirty glassware sit for long periods of time guarantees a harder cleaning job. Also take a minute to separate your glassware into a group which requires a higher degree of cleaning and one that does not.
your apparatus as soon as possible after you are finished with
it. Remove all stopcocks and stoppers from addition funnels, separatory
funnels and the like. Ground glass stopcocks and stoppers will
freeze in place if certain reactants (e. g., bases) were used in
them. Triple rinse all surfaces with an appropriate solvent to
remove traces of solvents and reaction mixtures, place these in
the appropriate waste container.
Health and Safety Considerations
a task as simple as washing glassware at the sink is potentially
hazardous. You must wear eye protection, appropriate for the task,
at all times. Gloves are recommended, even for general cleaning,
if the glassware contained an irritant, lachrymator or toxic material.
Before cleaning be sure that any excess reagent has been disposed
of properly and the vessel in which it was contained has been triple-rinsed
into the waste container.
The following steps should be followed for glassware for which a simple solvent rinse is not sufficient. If you need quantitatively clean glassware, these should be the first steps toward this goal, and more aggressive cleaning methods may be required (vide infra).
your glassware’s ground glass joints by wiping them with a paper
towel soaked in a small amount of ether, acetone or other solvent
(CAUTION! wear appropriate gloves and minimize your exposure to
water will sheet cleanly off the glass, if it is quantitatively
clean. If water does not sheet off the glass, and you desire the
glassware to be quantitatively clean, first repeat the above soaking
and scrubbing steps. If, after a second cleaning, bits of solid
still adhere to the glass, or if there is clearly a greasy residue
on the glass, more aggressive action must be taken.
More Aggressive Cleaning Methods
The following cleaning methods are two of the more commonly used ways to remove contaminants from glassware. They are usually used after normal cleaning has failed, and they are often used together, because each is effective at removing different types of contaminants. Care must be taken using either one because of the corrosive nature of the solutions used.
the contaminant is a metal-containing compound, soak the piece
of glassware in a 6 M HCl solution. DANGER! this
solution can cause severe burns! Wear appropriate gloves. Once
the solid has dissolved, copiously rinse the item with tap water,
and then repeat the general cleaning steps above. This method will
also remove some organic residues (not grease).
contaminated with metal-containing compounds
Even More Aggressive Cleaning Methods
Sometimes 6 M HCl and a base bath are not sufficient, and even more aggressive methods must be employed. CAUTION! all of these methods will do severe damage to the eyes, skin, mucous membranes and lungs. Extreme caution should be exercised when using these methods. Wear butyl gloves (not latex or nitrile exam gloves), eye protection and a lab coat. Work in the hood.
Undergraduate students must check with their faculty supervisor before using these methods, and they must be under the direct supervision of a faculty member at all times when using these methods (no exceptions).
Regia: This is an extremely powerful oxidizing solution
prepared from 1 part concentrated HNO3 and 3 parts concentrated
HCl (it is recommended that 1 part H2O be added if the aqua regia
will be stored to minimize the generation of Cl2). It is the
only acidic solution that will dissolve gold and will oxidize
just about everything else. Extreme caution must be used when
working with aqua regia because it generates Cl2 and NOx gases
in addition to causing severe tissue damage. Clean the glassware
before soaking in aqua regia and then rinse thoroughly with water.
you only need to rinse a cuvette in the appropriate solvent and
wipe the outside with a Kimwipe immediately after use. If something
has adhered itself to a cuvette, it is best to soak the cuvette
in solvent first and gently coax the solid off the side with a
cotton swab. Never use a brush on a cuvette! If this fails, one
of the acidic cleaning solutions mentioned above can be used (but
never HF!). It is not recommended that base bath be used on cuvettes,
because it tends to etch glass surfaces.
glassware that is not quantitatively clean can be dried by 1) placing
it on the drying rack (or invert on a paper towel), 2) placing
it in the drying oven (for items that are water-wet only, no flammable
solvents) or 3) rinsing with a solvent such as acetone, methanol
or ethanol and then gently blowing compressed air into the vessel
until it is dry. The first method (1) is preferred for drying quantitatively
clean glassware (provided that the prongs of the drying rack are
not inside the item, thus contaminating it). Volumetric glassware
and cuvettes are never to be placed in drying ovens, even if they
are not quantitatively clean. The third method is acceptable only
when the compressed air supply is known to be free oil and other
contaminants. An alternative to blowing air into the item is to
use an aspirator, or house vacuum, to pull air into the item.