Chapter 2: Chemicals, Apparatus, and Unit Operations of Analytical Chemistry Flashcards
Classifying chemicals
chemicals conform to the minimum standards set forth by the Reagent
Chemical Committee of the American Chemical Society (ACS)1 and are used whenever possible in analytical work.
reagent-grade chemicals
these kinds of reagent have been carefully analyzed by the supplier, and the results are printed on the container label.
primary standard chemicals
Meaning of NIST
National Institute of Standards and Technology
is an excellent source for primary standards. This agency also prepares and sells reference standards
NIST
are complex substances that have been exhaustively analyzed.
reference standards
3 different classifications of chemicals
Reagent grade
primary standard grade
special-purpose reagent chemicals
Chemicals that have been prepared for a specific application are also available.
Included among these are solvents for spectrophotometry and high-performance
liquid chromatography.
Special-Purpose Reagent Chemicals
TRUE or FALSE
Select the best grade of chemical available for analytical work. Whenever possible, pick the smallest bottle that is sufficient to do the job.
FALSE
TRUE or FALSE
Do not hold the stoppers of reagent bottles between your fingers. Never set a stopper on a desk top.
FALSE
TRUE or FALSE
Unless directed otherwise, never insert spatulas, spoons, or knives into a bottle that contains a solid chemical. Instead, shake the capped bottle vigorously or tap it gently against a wooden table to break up an encrustation. Then pour out the desired quantity. These measures are occasionally ineffective, and in such cases a clean porcelain spoon should be used.
TRUE
The apparatus should be washed with a ____________ and rinsed with _____________ and finally with ______________.
hot detergent; tap water; deionized water
TRUE or FALSE
It is seldom necessary to dry the interior
surface of glassware before use. Drying is usually a waste of time and is always a potential source of contamination
TRUE
TRUE or FALSE
An organic solvent, such as methyl ethyl ketone or acetone, may be effective in
removing grease films.
TRUE
is the sudden, often violent
boiling that tends to spatter solution
out of its container.
bumping
is the oxidation of the
organic constituents of a sample with
oxidizing reagents such as nitric acid,
sulfuric acid, hydrogen peroxide, aqueous
bromine, or a combination of
these reagents.
wet ashing
may also minimize bumping if their use is permissible
glass beads
TRUE or FALSE
Organic constituents can frequently be eliminated from a solution by adding sulfuric acid and heating to the appearance of sulfur trioxide fumes (in a hood).
TRUE
must be used to measure masses with high accuracy.
analytical balance
is an instrument for determining mass with a maximum capacity
that ranges from 1 g to a few kilograms with a precision of at least 1 part in
105 at maximum capacity.
analytical balance
TRUE or FALSE
The precision and accuracy of many modern analytical balances exceed 1 part in 10^6 at full capacity.
TRUE
Types of analytical balance
macrobalances
semimicroanalytical balances
microanalytical balance
have a maximum capacity
ranging between 160 and 200 g. With these balances, measurements can be made with a standard deviation of 60.1 mg.
macrobalances
have a maximum
loading of 10 to 30 g with a precision of 60.01 mg
Semimicroanalytical balances
has a capacity of 1 to 3 g and a precision of 60.001 mg (1 μg).
microanalytical balance
first known analytical balance in history is called
equal arm balance
is the mass of an empty sample
container.
tare
is the process of
setting a balance to read zero in the presence of the tare
taring
In a single-pan balance, the small transparent screen mounted on the beam, is scribed with a scale that reads 0 to 100 mg
reticle
Precautions in using an analytical balance
- center the load on the pan
- protect the balance from corrosion
- observe special precautions for the weighing of liquids
- consult the instructor if the balance appears to need adjustment
- Keep the balance and its case scrupulously clean
- cool the sample (room temp.) before weighing it
- use tongs, finger pads, or a glassine paper strip to handle dried objects to prevent transferring moisture
is the weighing error that develops when the object being weighed has a significantly different density than the masses.
buoyancy
TRUE or FALSE
Always allow heated objects
to return to room temperature
before you attempt to weigh
them
TRUE
Name two temperature effect factors that lead to erroneous balance reading
convection current (exert a buoyant effect on the pan and the object)
warm air trapped (weigh less than the same volume at a lower temp)
Other source of error in weighing
static charge from porcelain or glass object (especially when humidity is low.
less precise than analytical balances find extensive use in the analytical
laboratory, offering the advantages of speed, ruggedness, large capacity, and convenience.
auxiliary balances
accommodate 150 to 200 g with a precision of about 1 mg—an order
of magnitude less than a macroanalytical balance
top-loading balance
is less sensitive than a typical top-loading auxiliary balance is also useful. This single-pan balance has three decades of masses that slide along individually calibrated scales.
triple beam balance
TRUE or FALSE
Use auxiliary laboratory balances
for determining masses that do
not require great accuracy.
is a process in which a solid is cycled
through heating, cooling, and weighing
steps until its mass becomes constant
to within 0.2 to 0.3 mg.
drying or ignition to constant mass
TRUE or FALSE
The mass of many solids changes with humidity because they tend to absorb weighable amounts of moisture.
TRUE
Constant weighing is repeated as many times as needed to obtain successive masses that agree within
0.2 to 0.3 mg of one another.
Containers that are convenient for drying and storing solids
weighing bottles
is a principal advantage of using plastic weighing bottles rather than glass, but plastic abrades easily and is not as easily cleaned as glass.
ruggedness
the most common way of removing moisture from solids.
oven drying
The base section of a desiccator contains a chemical drying agent called
desiccants
Desiccants can be
anhydrous calcium chloride
calcium sulfate (Drierite),
anhydrous magnesium perchlorate (Anhydrone or Dehydrite), or
phosphorus pentoxide
Very hygroscopic materials should be stored in containers equipped with snug
covers, such as
weighing bottles
What can you use to avoid touching dried objects with your fingers
tongs, chamois finger cots clean cotton gloves, strips of paper
a simple method for determining a series of sample masses. weight of empty beaker- weight of beaker with precipitates
weighing by difference
How will you weigh hygroscopic solids?
- a weighing bottle is needed
- place the approximate amount of sample needed in the individual bottles and heat for an appropriate time
- when heating is complete, quickly cap the bottles and cool in the desiccator.
The mass of a liquid is always obtained by
weighing by difference
Noncorrosive liquids
and relatively nonvolatile can be transferred to previously weighed containers with
snugly fitting covers (such as
weighing bottles
A volatile or corrosive liquid should be sealed in a weighed
GLASS AMPOULE
Simple crucibles serve as containers, which can be ________, _______________, _____________,__________ that maintains constant mass-within the limits of experimental error.
porcelain
aluminum oxide
silica
platinum
crucibles that are used as containers for the high-temperature fusion of samples that are not soluble in aqueous reagents
simple crucibles of nickel, iron, and gold
what kind of crucibles serve not only as containers but also as filters.
filtering crucibles
It used during filtration to hasten the filtering process
vacuum
Apparatus in filtration and ignition of solids
simple crucibles
filtering crucibles
filter paper
also called as fritted -glass crucibles that are manufactures in fine, medium, and coarse porosities (marked f, m, and c), with upper temp limit about 200 C
sintered-glass
Filtering crucibles made entirely of
__________can tolerate substantially higher temperatures without damage
quartz
this type of crucible has a perforated bottom that supports a fibrous mat
gooch crucible
was at one time the filtering medium of choice for a Gooch crucible, which was eliminated and replaced by small circles of glass matting
asbestos
is manufactured from cellulose
fibers that have been treated with hydrochloric and hydrofluoric acids to remove metallic impurities and silica; ammonia is then used to neutralize the acids. The residual ammonium salts in many filter papers may be sufficient to affect the analysis for nitrogen by the Kjeldahl method
ashless paper
are currently quite popular, and where applicable, they greatly shorten drying cycles. For example, slurry samples that require 12 to 16 hours for drying in a conventional oven are reported to be dried within 5 to 6 minutes in a microwave oven.
microwave laboratory ovens
order of burners that provides highest temp
meker burner
tirrill
bunsen types
what do you call a “heavy-duty electric furnace” that is capable of maintaining controlled temperatures of 1100 C or higher
muffle furnace
are needed for protection when transferring objects to or from such a furnace
Long-handled tongs
heat-resistant gloves
filtering crucibles are conveniently cleaned by
backwashing on a filtration train
steps in filtering an analytical precipitate
decantation
washing
transfer
what filtering analytical process
“as much supernatant liquid as possible is passed through the filter while the precipitated solid is kept essentially undisturbed in the beaker where it was formed.”
decantation
speeds the overall filtration rate by delaying the time at which the pores of the filtering medium become clogged with precipitate
decantation
is used to direct the flow of the decanted liquid
stirring rod
The last traces of precipitate that cling to the inside of the beaker are dislodged
with a _______________, which is a small section of rubber tubing that has been
crimped on one end.
rubber policeman
TRUE or FALSE
Filters are filled to more than
three-quarters of capacity to prevent the possible loss of precipitate through creeping
FALSE
Filters are never filled to more than
three-quarters of capacity to prevent the possible loss of precipitate through creeping
TRUE or FALSE
A gelatinous precipitate must be completely washed before it is allowed to dry. These precipitates shrink and develop cracks as they dry.
TRUE
TRUE or FALSE
Seating is completed by dampening the cone with water from a wash bottle and gently patting it with a finger
TRUE
In ashing filter papers, if a heat lamp is used, crucibles are placed on a clean, nonreactive surface such as a wire screen converted with aluminum foil, which is positioned about
1 cm above the rim of the crucible and turned on
TRUE or FALSE
Heating should start with a big flame
FALSE
is used when a filtering crucible can be used
instead of paper. The trap isolates the filter flask from the source of vacuum.
vacuum filtration train
TRUE or FALSE
Never place a heated object on the benchtop. Instead, place it on a wire gauze or a
heat-resistant ceramic plate.
TRUE
TRUE or FALSE
Keep the tongs and forceps used to handle heated objects scrupulously clean. In
particular, do not allow the tips to touch the benchtop.
TRUE
TRUE or FALSE
The volume occupied by a given mass of liquid does not vary with temperature, as does the device that holds the liquid during the measurement
FALSE
The volume occupied by a given mass of liquid varies with temperature, as does the
a device that holds the liquid during the measurement
Most volumetric measuring devices are made of __________, which has a _________
glass; small coefficient of expansion
TRUE or FALSE
The coefficient of expansion for dilute aqueous solutions (approximately
0.025%/°C) is such that a 5°C change has a measurable effect on the reliability of
ordinary volumetric measurements.
TRUE
What class glassware is manufactured to the
highest tolerances from Pyrex,
borosilicate, or Kimax glass
Class A glassware
also called economy ware have tolerances that are about twice those of Class A.
Class B glassware
volume may be measured reliably with
pipet
buret
volumetric flask
TRUE or FALSE
Volumetric equipment is marked by the manufacturer to indicate not only the
manner of calibration (usually TD for “to deliver” or TC for “to contain”) but also
the temperature at which the calibration strictly applies
TRUE
permit the transfer of accurately known volumes from one container to another
pipets
delivers a single fixed volume between 0.5 and 200 mL
volumetric, or transfer pipet
are calibrated in convenient units to permit delivery of any volume up to a maximum
capacity ranging from 0.1 to 25 mL
measuring pipets
deliver adjustable microliter volumes of liquid. With these pipets, a known and adjustable volume of air is displaced from the plastic disposable tip by depressing the
pushbutton on the top of the pipet to a first stop
Handheld Eppendorf micropipets
TRUE or FALSE
The accuracy and precision of automatic pipets depend somewhat on the skill and experience of the operators and thus should be calibrated for critical work.
TRUE
like measuring pipets, make it possible to deliver any volume up to the maximum
capacity of the device. The precision attainable with a ______ is substantially
greater than the precision with a pipet
buret
What do you calibrate in a buret
tube/calibrated tube
are manufactured with capacities ranging from 5 mL to 5 L and are usually calibrated to contain (TC) a specified volume when filled
to a line etched on the neck.
volumetric flask
They are used for the preparation of standard solutions and for the dilution of samples to a fixed volume prior to taking aliquots with a pipet
volumetric flasks
What do you wash with a dirty glassware
warm detergent solution
TRUE or FALSE
Prolonged soaking should be avoided
because a rough area or ring is likely to develop at a detergent/air interface. This
ring cannot be removed and causes a film break that destroys the usefulness of the
equipment.
TRUE
The top surface of a liquid confined in a narrow tube exhibits a marked curvature or also known as
meniscus
is the curved surface
of a liquid at its interface with the
atmosphere.
meniscus
is the apparent displacement
of a liquid level or of a pointer as an
observer changes position. It also
occurs when an object is viewed from
a position that is not at a right angle to
the object.
parralax
TRUE or FALSE
Never pipet by mouth because there is risk of accidentally ingesting the liquid being pipetted.
TRUE
What would you use to suction liquid into a pipet
rubber suction bulb
is a measured fraction of
the volume of a liquid sample.
aliquot
Cleaning
Draw detergent solution to a level _____ cm above the calibration mark of the pipet.
2 to 3
fill the pipet with distilled water to perhaps ____________ of its capacity and carefully rotate it so that the entire interior surface is wetted.
one-third
In measuring an aliquot, the first thing you will do is
acclimatize the pipet with the solution of interest
TRUE or FALSE
Be sure that there are no bubbles in the bulk of the liquid or foam at the
surface
TRUE
TRUE or FALSE
The small volume remaining inside the tip of a volumetric pipet should not be
blown or rinsed into the receiving vessel
TRUE
TRUE or FALSE
Buret readings should be
estimated to the nearest 0.01 mL.
True
A proper amount of lubricant has been used
when
- area of a stopcock and barrel appears nearly transparent
- seal is liquid tight.
- no grease as worked its way into the tip
Clean grease films by
organic solvents such as acetone or alcohol and thorough washing of detergent
TRUE or FALSE
fouling of a buret tip with stopcock grease
is not a serious matter. Removal is best accomplished with organic solvents. A stoppage during a titration can be freed by gentle warming of the tip with a lighted match
TRUE
TRUE or FALSE
The solute should be completely
dissolved before you dilute to the
mark
TRUE
In filling the buret with a solution, Make certain the stopcock is closed. Add 5 to 10 mL of the titrant, and carefully rotate the buret to wet the interior completely. Allow the liquid to drain through the tip. Repeat this procedure at least two more times.
TRUE
How do you dry a volumetric flask?
by clamping the flask in an inverted position
insertion of a glass tube connected to a vacuum line hastens the process
use of __________ minimizes the possibility of losing solid during the transfer of mass of solute to a volumetric flask
powder funnel
Quantitative transfer of liquid to a volumetric flask
With the stirring rod, tip off the
last drop of liquid on the spout of the beaker. Rinse both the stirring rod and the
interior of the beaker with distilled water and transfer the washings to the volumetric
flask as before. Repeat the rinsing process at least two more times.
the liquid level accidentally exceeds the calibration mark, the solution can be saved by correcting for the excess volume using a
selfstick label
TRUE or FALSE
Use a selfstick label to mark the location of the meniscus. After the flask has been emptied, carefully refill it to the manufacturer’s etched mark with water. Use a buret to determine the additional volume needed to fill the flask so that the meniscus is at the gummed-label mark. This volume must be added to the nominal volume of the flask when calculating the concentration of the solution.
TRUE
a type of glassware that is calibrated by measuring the mass of a liquid (usually
distilled or deionized water) of known density and temperature that is contained
in (or delivered by) the volumetric ware.
Volumetric glassware
TRUE or FALSE
All volumetric ware should be painstakingly freed of water breaks before being calibrated
TRUE
TRUE or FALSE
Burets and pipets need not be dry, but volumetric flasks should be thoroughly
drained and dried at room temperature
is needed to record measurements and observations concerning an analysis.
laboratory notebook
TRUE or FALSE
In maintaining the laboratory notebook,you supply each entry or series of entries with a heading or label
TRUE
TRUE or FALSE
Record all data and observations directly into the notebook in ink.
TRUE
TRUE or FALSE
Do not date each page of the notebook as it is used.
FALSE
TRUE or FALSE
Never attempt to erase or obliterate an incorrect entry. Instead, cross it out with
a single horizontal line and locate the correct entry as nearby as possible. Do not
write over incorrect numbers. With time, it may become impossible to distinguish
the correct entry from the incorrect one.
TRUE
TRUE or FALSE
You can remove a page from the notebook.
FALSE
draw diagonal line
