 |
 |
19 of 36 |  |
 |
 |
19
IV. LABORATORY TECHNIQUES & EQUIPMENT
A.
Mass Measurements
Electronic balances will be used to determine
the masses of samples. To make the weighing
process efficient, two types of electronic
balances will be incorporated in a specified weighing
technique. The first type is a general
purpose balance, that has a large flat open pan and is
accurate to 0.01 g. The second type
is an analytical balance, which is accurate
to 0.001 g and
has a glass weigh chamber to prevent air
currents from causing the mass readings to fluctuate.
The following steps outline the weighing
technique that is to be used in this course.
1.
Zero the analytical balance to 0.000 g
±0.001 g by gently pressing the re-zero bar on the front
of the balance.
2.
Put the empty container on the analytical
balance. The EXACT mass of this empty container
will be shown on the display. RECORD
this mass on your Observations Sheet.
3.
Transfer the empty container to the general
purpose balance, then TARE the balance by gently
pressing the re-zero bar on the front
of this balance. The balance display will show 0.00 g.
4.
Carefully add the approximate mass of
sample to the container, monitoring the display as the
solid is added. If excess solid
sample is taken, the excess must be disposed of in the “solid
waste” container
on the balance table. If any solid is spilt
on or near the balance, clean it
up immediately.
5.
Return the container plus sample to the
analytical balance to determine the exact mass of the
container plus solid. RECORD
this mass on your Observations Sheet.
NOTE:
a) Be sure the scoop is clean
and dry BEFORE placing it in a reagent container.
b) Chemicals are NEVER
to be handled over top of the analytical balances.
c) Any excess solid taken must
be disposed of in the “solid waste”
container
on the balance table and must NEVER be
returned to the reagent bottle.
