Laboratory Techniques
Section 3L
Chemistry I & II
1
Laboratory Techniques
To ensure safety, correct laboratory
techniques should be used at
all times!!
Refer back to this section of notes any time you
are unsure of proper laboratory technique.
If proper technique/lab safety is not followed, you
will receive a violation notice which could
result in a warning, loss of points, and/or loss
of all laboratory privileges.
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Before you begin…
1.
Always read the label on a reagent
bottle before using its contents.
Always wear safety goggles when
handling chemicals.
Never touch chemicals with your hands.
Never return unused chemicals to their
original containers.
2.
3.
4.
a.
To avoid waste, do not take excessive
amounts of reagents.
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NFPA Diamond Label
1.
National Fire Protection Association
diamond indicates flammability,
reactivity, health concerns, and other
potential hazards associated with the
reagent.
A.
Numbers are used to rate potential hazards
on a scale from 0 (least hazardous) to 4
(most hazardous)
4
NFPA Diamond Level
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Material Safety Data Sheet
1.
Additional information can be found
about each chemical on a MSDS (see
example MSDS).
It is divided into 16 sections, containing
4 types of information
2.
A.
Critical Emergency Information
1)
2)
3)
4)
Substance identity
Manufacturer
Hazardous components
Identification of the hazards
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Material Safety Data Sheet
B.
Emergency Response Measures
1)
2)
3)
C.
First aid
Fire-fighting
Accidental Release
Personal Protection and Exposure Measures
1)
2)
3)
4)
5)
Handling and storage
Personal Protection Equipment
Exposure controls
Physical and Chemical Properties
Stability and reactivity of the substance
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Material Safety Data Sheet
D. Other useful information
1)
2)
3)
4)
Toxicological and ecological effects
Disposal considerations
Transport and regulatory information
Miscellaneous information
The layout and exact contents of MSDSs
vary from supplier to supplier.
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Techniques Used in the Lab
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Pouring Liquids
1.
Use the back of your fingers to remove
the stopper from the reagent bottle.
A.
B.
2.
Hold the stopper between your fingers until
the transfer is complete
Do not place the stopper on the lab station.
Grasp the container from which you are
pouring with the palm of your hand
covering the label.
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Pouring Liquids
3.
When you are transferring a liquid to a
test tube or graduated cylinder, the
container should be held at eye level.
a.
4.
Pour the liquid slowly until the correct
volume has been transferred.
When you are pouring a liquid from a
reagent bottle into a beaker, the reagent
should be poured slowly down a glass
stirring rod.
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Transferring Liquids
1.
Using a dropper bottle
A.
B.
2.
Never lay the dropper on any surface.
Be sure the dropper never touches your container
or its contents.
Using a Beral or Pasteur Pipet
A.
Do not pipet directly from the reagent bottle unless
instructed to do so.
1)
B.
Instead, pour some of the liquid into a labeled container
and pipet from your container
Do not touch the container or its contents with the
tip of the pipet
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Mixing Liquids
1.
To dilute concentrated liquids with
water, ALWAYS add the concentrated
reagent to the water slowly.
A.
This is especially important to follow when
adding a concentrated acid to water
1)
Because of the large amount of heat generated
by this combination splattering can occur.
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Mixing a Solid and a Liquid
1.
2.
Add the solid to the liquid while stirring
continuously.
Add the solid in small amounts, unless
instructed otherwise.
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Filtering a Mixture
1.
Sometimes it is necessary to separate a
solid from a liquid – filtration is
necessary.
A.
B.
Fold a paper circle in half and then in
quarters.
Open the folded paper to form a cone
1)
One thickness of paper on one side and three
thicknesses on the other
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Filtering a Mixture
C.
Put the paper cone in a filter funnel.
1)
Place the funnel in an iron ring clamped to a ring
stand.
Moisten the filter paper with a small volume of
distilled water and gently press the paper against
the sides of the funnel.
Place a beaker beneath the funnel to collect the
filtrate.
2)
3)
a.
The tip of the funnel should touch the inside surface of the
beaker and extend about one inch below the rim.
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Filtering a Mixture
D. Decant the liquid from the solid by
pouring it down a glass stirring rod into
the funnel.
1)
2)
Be careful to keep the liquid below the top
edge of the cone of filter paper at all times
– the liquid must not overflow.
Use distilled water from a wash bottle to
wash the solid into the filter.
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Filtering a Mixture
E.
F.
When the filtration is complete, wash
the solid residue on the filter paper with
distilled water to remove traces of
solvent – dry the solid.
If the filtrate contains a dissolved salt, it
may be recovered by evaporation if
desired.
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20
Heating Liquids
1.
Heating a liquid in a test tube:
A.
B.
C.
D.
E.
Adjust the gas burner to produce a gentle blue
flame
Fill a test tube one-third full with the liquid to be
heated.
Grasp the test tube with a test tube holder, near
the upper end of the test tube.
Hold the test tube in a slanting position in the
flame, and gently heat the tube a short distance
below the surface of the liquid
Shake the test tube gently as it is being heated,
until the liquid boils or reaches the desired
temperature.
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Heating Liquids
CAUTION:
NEVER point the open end of a test tube
you are heating either toward yourself
or anyone working nearby.
NEVER heat the bottom of the test tube.
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Heating Liquids
2.
Heating a Liquid in a Beaker (assembling a
water bath)
A.
B.
C.
D.
E.
Fasten an iron ring securely to a ring stand so that
it is 2-4 cm above the top of a gas burner placed
on the ring stand base.
Place a beaker half-filled with water on a wire
gauze resting on the iron ring.
Light your gas burner and adjust it to produce a
hot flame.
Place the burner beneath the wire gauze.
A hot plate can also be used in place of the gas
burner.
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Heating Liquids
CAUTION:
NEVER heat plastic beakers or graduated
glassware in a burner flame.
NEVER let boiling water boil dry – add water
to it as necessary.
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Measuring Volume
1.
Volume measurements can be accurate
or approximate.
A.
B.
Most volume measures in the lab are made
using equipment calibrated in milliliters.
Although some beakers have graduation
marks, these marks are designed only for
quick, rough estimates of volume.
1)
Accurate volumes must be measured with
pipets, burets, or volumetric flasks.
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Measuring Volume
2.
Using a graduated cylinder:
A.
B.
A volume measurement is always read at
the bottom of the meniscus – curved
surface where the water comes in contact
with the cylinder walls
Measurements should always be one place
more than the graduation marks on the
cylinder.
1)
2)
Example: 100mL broken up into 1mL
increments – read to 0.1mL
Always estimate between the smallest marks
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29
Measuring Volume
3.
Using a pipet
A.
B.
A pipet is used to accurately measure and
deliver volumes of liquids.
Two Types:
1)
2)
Volumetric – has single calibration mark and
delivers the volume printed on the bulb of the
pipet at the temperature specified.
Graduated – has calibration marks along the
length of the pipet.
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Measuring Volume
C. Using a volumetric pipet (more accurate
than graduated pipet)
1)
Place the tip of the pipet below the surface
of the liquid to be dispensed.
Compress a pipet bulb and press the hole
in the bulb against the upper end of the
pipet.
2)
a.
b.
Never push the pipet bulb over the end of the
pipet
Never fill a pipet by applying suction with your
mouth.
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Measuring Volume
3)
4)
5)
Slowly release pressure on the bulb so that
liquid is drawn into the pipet to a level about 2
cm about the calibration mark
Remove the bulb and simultaneously place
your index finger over the end of the pipet
Keep your index finger pressed firmly against
the end and withdraw the pipet from the liquid
and carefully wipe the outside with a paper
towel.
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Measuring Volume
6)
Slowly reduce the pressure on your finger to
allow the excess liquid to drain into a waste
container until the bottom of the meniscus is
at the calibration mark.
Deliver the remaining liquid in the pipet to the
designated container.
7)
a.
b.
Let it drain completely.
Wait 20 seconds, and touch the tip of the pipet to
the side of the flask or surface of the liquid. A very
small amount will remain in the pipet.
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34
Measuring Volume
D. Using a Buret
1)
A buret is a long, narrow, calibrated tube
with a device at one end to control the flow
of liquid from the buret.
a.
2)
These measurements are more precise than
those made using a pipet.
Burets differ in the type of flow-control
device, or valve, that is used
a.
b.
Tapered glass stopcock at the end of a glass
barrel
Teflon stopcock attached to glass/Teflon barrel
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36
Measuring Volume
3)
How to use a buret:
a.
Before using a buret, check to see that the
stopcock is liquid tight by closing the
stopcock and filling the buret with water –
report any leaks
Begin by rinsing the buret three or more
times with small portions of the solution to
be used in the buret.
b.
i.
Dispose of the rinses as specified
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Measuring Volume
c.
d.
e.
Clamp the buret vertically to a ring
stand.
Close the stopcock and use a shortstem funnel to slowly fill the buret with
the sample solution.
Fill the buret to above the zero
calibration mark at the top. Remove the
funnel
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Measuring Volume
f.
Place a discard beaker under the
stopcock, open the stopcock, and drain
the solution until the meniscus is at, or
slightly below, the zero calibration mark.
To remove the hanging drop, touch the
wet inside wall of the beaker with the
buret tip.
g.
i.
Replace the discard beaker with a flask
that you want to dispense the liquid into.
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Measuring Volume
f.
When using a buret with a Teflon
stopcock, operate the stopcocks with
either hand without the risk of the
stopcock slipping out.
i.
Glass stopcocks should be operated with
the hand on the opposite side of the buret
barrel from the stopcock, to avoid pulling
the stopcock from the barrel.
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Measuring Volume
g.
Drain the solution from the buret
relatively slowly.
After you have drained the desired
volume, close the stopcock.
Touch the inner wall of the flask to the
buret tip to remove the hanging drop.
h.
i.
i.
Use distilled water from a wash bottle to
rinse the drop into the liquid in the flask.
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Measuring Volume
4)
Maintaining the buret
a.
Teflon stopcocks do not need lubrication,
but glass stopcocks require a thin film of
stopcock grease
To lubricate the glass stopcock:
b.
i.
ii.
iii.
Carefully remove the stopcock from the barrel
and remove any old grease.
Place a small amount of grease on the stopcock
surface avoiding the area near the hole.
Insert the stopcock into the barrel and rotate
several times.
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43
Measuring Volume
E.
Using a volumetric flask
1)
2)
3)
Volumetric flasks are calibrated to contain a
specified volume.
The single calibration mark is located on
the narrow neck to allow filling to a
reproducible volumes
They are used to prepare solutions in two
general ways:
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Measuring Volume
a.
Dissolving a solid solute to make a
solution of a definite volume.
i.
ii.
iii.
Weigh the solute and dissolve in the
minimum amount of solvent in a clean
beaker
Using a funnel, transfer the solution to a
volumetric flask.
Rinse the beaker with a small amount of
the solvent and transfer the rinse through
the funnel into the flask.
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Measuring Volume
b.
Quantitative dilution of a concentrated
solution
i.
c.
Use a pipet to transfer an accurately
measured sample of the concentrated
solution to the volumetric flask
With either procedure, add more solvent
to the flask until it is about 2/3 full, while
slowly swirling the flask to agitate the
solution.
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Measuring Volume
d.
e.
f.
g.
Continue slowly adding more solvent until the
liquid level is just below the calibration mark.
Stopper the flask and thoroughly mix the
solution by inverting the flask end over end.
Use a small dropper or pipet to add the final
amount of solvent needed to align the bottom
of the meniscus with the calibration mark.
Stopper the flask, invert to mix, and transfer
to a storage container.
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48
Using a Gas Burner
1.
Identify the model of burner
A.
Two Types:
1)
2)
2.
Bunsen Burner – has adjustable air vents
Tirrell Burner – has adjustable air vents and a
gas control valve in its base.
For proper procedure see:
A.
Lab: Lighting a Gas Burner
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Using a Hot Plate
1.
2.
A hot plate is an electrical device that is
particularly useful for experiments
where an open flame is prohibited.
A dial or knob controls the hot plate
temperature.
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Heating a Solid
1.
Porcelain crucibles are used for heating
solids to thermally decompose the solids or to
heat them to dryness.
A.
B.
C.
D.
The empty crucible should first be heated to drive
off any moisture. Allow to cool.
Place the solid to be heated into the crucible.
To heat the sample and not allow it to react with
the atmospheric oxygen, insert the covered
crucible upright in the clay triangle with the cover
on straight.
To hear the sample and allow it to react with the
atmospheric oxygen, tilt the crucible slightly in the
clay triangle, and use crucible tongs to position the
cover so it is slightly ajar.
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