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PRESENTER: The balance is
arguably the most used piece

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of equipment in the
chemistry laboratory.

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However, only proper technique,
care, and maintenance

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will allow accurate measurements
and will keep the balance

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functioning correctly.

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A balance is used to determine
the mass of a solid or liquid.

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You should remember
that mass is defined

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as a measure of the amount of
matter, regardless of location,

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and that weight is defined
as the force resulting

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from gravity, which varies
from place to place depending

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on the distance from
the center of the Earth.

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Because weight is directly
proportional to mass

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on any location on Earth,
we will use these terms

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interchangeably.

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If you decide to do
some space travel,

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however, take care to
remember the differences.

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Four major types of
balances are commonly

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used, the triple beam balance,
the top-loading balance,

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the analytical balance, and
the microanalytical balance.

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The difference
between these balances

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is the amount of
precision they afford.

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The triple beam balance is
precise to 10 milligrams,

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the top-loading to 1 milligram,
the analytical to 1/10

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of a milligram, and the
microanalytical to 1/1,000

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of a milligram.

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Precision comes at
a cost, however.

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As precision increases,
so does the susceptibility

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of the balance to
environmental conditions

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as well as balanced cost.

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Therefore, you should choose
a balance that is only

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as precise as necessary.

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The two balances that you
will most commonly encounter

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include the top-loading balance
and the analytical balance.

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The top-loading
balance is typically

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used for rough measurements
or for weighing chemicals

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that will be used in excess.

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The analytical balance is
used when precise measurements

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are desired.

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This video will focus on the
use, care, and maintenance

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of an analytical balance.

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The topics discussed
can be extrapolated

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to the top-loading
balance as well.

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To weigh an object on
an analytical balance,

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turn the balance on if
it is not on already

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and allow it to warm
up for 30 minutes.

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Inspect the balance and
make sure that it is clean.

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If necessary, clean
off the balance pan

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with a soft painter's brush.

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Make sure the doors are closed
and press the control bar

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to tare the balance.

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A reading of 0.0 milligrams
with no other display

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should appear if the
balance is stable.

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Gently place the
object to be weighed

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in the center of the balance
pan, close the doors,

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and record the weight that
is indicated on the display

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after the numbers have
ceased to fluctuate.

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Remove the object
from the balance pan

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and repeat the process two
more times to ensure precision.

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Finally, average the three
readings to determine

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the weight of the object.

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When weighing a
chemical, care must

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be taken to never
allow the chemical

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to touch the balanced pan.

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Instead, weigh the chemical
in an appropriate container.

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If possible, weigh
the chemical directly

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into the destination vessel.

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This action eliminates
the transfer step

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and the potential
loss of material.

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If using the destination
vessel is not possible,

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choose the smallest weigh
boat or piece of paper

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that will effectively hold the
desired amount of chemical.

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The heavier the container,
the less accurate

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the measurement because
just a small weight

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difference will exist between
relatively large numbers.

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In addition, the more
surface area, the more

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places for chemicals to stick
to instead of being transferred

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to the destination vessel.

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Place the weighing container
on the balance pan,

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close the doors,
and tare the balance

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if you are using
weigh paper, first,

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crease the paper
along the diagonal

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to facilitate the
transfer of chemicals.

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Remove the weighing
vessel from the balance

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and load an estimated
amount of chemical

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onto it with a spatula.

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Placed the loaded weighing
vessel back on the balance

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pan and close the doors
to obtain a reading.

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If the weight is too high,
take the weigh vessel

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off the balance pan and
transfer the excess chemical

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into an appropriate
waste container,

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never back into the
original reagent bottle.

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If the weight is too low,
introduce more chemicals

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to the weigh container.

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Remove the weigh
vessel from the balance

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pan every time additional
chemical is introduced.

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Finally, transfer the
chemical from the waste paper

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or weigh boat into the
appropriate reaction vessel.

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Reweigh the paper
boat to determine

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the exact amount of chemical
that was transferred.

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After finishing
with the balance,

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use a soft brush to clean up
any solids from the balance pan

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and wipe up any liquids.

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Close the doors to
prevent dust and dirt

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from entering the balance.

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Clean the surrounding
area and remove all items

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that you brought there.

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Leave the balance and
area surrounding it

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in better shape than
when you found it.

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The accuracy of
your measurements

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depends on both good technique
and environmental factors.

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This video will highlight
the most important

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of these guidelines.

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Keep the balance doors
closed at all times

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to prevent air currents
from causing the balance pan

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to bounce slightly.

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Never lean or lay a hand
on the balance table

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to prevent unstable
measurements.

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Wear gloves to prevent
oil from depositing

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on the glassware which
falsely increases the mass.

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Weigh a chemical directly
into the reaction vessel.

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If that is not possible,
use the smallest weigh boat

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or weigh paper that
will hold your desired

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amount of chemical.

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Ensure that the outside
of the way vessel

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is completely dry before
placing it on the balance pan,

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and be sure to place the object
on the center of the balance

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pan.

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Allow moist chemicals
to dry completely

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to avoid elevated
readings and avoid

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breathing on an object which
condenses moisture on it

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and falsely increases its mass.

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Weigh ultra dry objects
or ones immediately

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removed from a desiccator
at identical time intervals

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because they absorb
moisture and gain weight

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the longer they sit
in the atmosphere.

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Finally, allow hot
or cold objects

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to reach room temperature
before weighing.

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A hot object should be
cooled in a desiccator

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to prevent the pick
up of moisture.

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Hot or cold objects create a
convection current in the air

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around the balance
pan, which reduces

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the air pressure
on the balance pan

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and results in an
unstable reading.

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The accuracy of a
measurement is only

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as good as the
instrument that is used.

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To keep your balance
functioning correctly,

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the following precautions
should be taken.

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Never weigh chemicals
directly on the balance pan.

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Never add chemicals
to the weighing vessel

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while it is on the balance pan.

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Never pour a chemical directly
out of a reagent bottle

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and into the weigh vessel.

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Use a spatula instead.

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Pay attention to
the maximum weight

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allowed by a particular
balance and do not overload it.

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When using a balance,
be aware of the warning

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signs which indicate that the
balance is malfunctioning.

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After recording the
weight of a chemical,

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remove it from the balance pan.

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The numbers and the
display should again

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read 0.0 milligrams.

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If the displayed value is
0.3 milligrams or greater,

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then the 0 level
was significantly

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shifted during the
weighing process

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and the chemical
must be reweighed.

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Check the amount of
drift that is occurring.

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Drift is characterized by weight
readings that do not stabilize

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or by unstable readings
with no weight applied.

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All analytical balances show
some degree of fluctuation

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on their display
and care should be

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taken to keep this
shift at a minimum.

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If you notice a change in
the amount of instability

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on a particular balance,
then it is malfunctioning.

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Drift is affected by two
environmental factors,

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temperature and
static electricity.

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It can be minimized
through their manipulation.

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The temperature of the room
and the internal temperature

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of the balance should be kept
constant within 2 degrees

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Celsius.

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Static electricity
can be minimized

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by avoiding the use
of plastic containers

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and by maintaining the
humidity above 40%.

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If you notice excessive drift,
the following situations

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may be occurring.

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The balance may be
exposed to a draft.

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Close the doors.

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The sample may be moist
and undergoing evaporation

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on the balance pan.

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The sample might be ultra
dry and absorbing moisture

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on the balance pan.

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The sample may not be at ambient
temperature, which causes it

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to produce convection currents.

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The sample may be electrostatic.

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If you notice drift
while weighing a sample,

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the most accurate reading
is the first number

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that appeared and was
maintained for two seconds.

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So far, we've discussed
the use of a balance

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for weighing solids,
however, a balance

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may also be used to
weigh liquid samples.

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Generally, it is easier and
more accurate to determine

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the volume of a liquid by using
precision volumetric glassware,

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such as a burette,
glass pipette, syringe,

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or automatic pipette, and
then use the liquid's density

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to calculate its mass.

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However, directly measuring
the weight of a liquid

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is preferred in some
situations, such as when

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working with a vicious liquid.

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As a final note, when
weighing a volatile liquid

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or one that evaporates
readily, use a weighing bottle

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with a lid.

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Although using a balance is
a relatively simple task,

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accurate measurements
can only be

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ensured through good technique.

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Exceptional care must
be taken to maintain

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a clean environment which helps
to keep the balance functioning

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properly.

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[MUSIC PLAYING]