The balances used in
this lab are delicate (EXPENSIVE!)
instruments, the following general rules should be observed while using
them.
Treat them as your own precious
property:
Keep the balance scrupulously clean.
Do not move the balance while they are on.
Handle all masses and objects with forceps or tweezers, NEVER with
your fingers.
Place objects to be weighed as close as possible to the center
of the weighing pan. DO NOT drop
items onto the balance.
Do not weight hot objects. Allow them to cool to room
temperature first.
Never place moist objects or chemicals directly on the balance
pan.
Use proper weighing paper or dishes when determining the mass of
a
solid.
When determining the mass by difference, never pour solid or
liquid
chemicals into the beaker or flask while it is on the balance.
First
remove the container, and then add the appropriate amount of
chemical.
Then return the container to the pan to complete the mass determination.
Record the mass DIRECTLY into
your notebook. Never add or subtract mentally.
While determining the mass of an object, use the same balance
for
the entire experiment.
The balances in the lab will weigh to three decimal places out
to
300 g. ALWAYS
report all of digits in the mass.
Close chemical containers after use.
To directly determine an object's
mass:
Check that the balance is on, that the lid is closed, and it is
properly zeroed. An '*' will be in the upper left hand corner of
the display, and the mass should read as 0.000 g. If you do not
see both of these, push the 'Tare' button and wait 5-10 seconds for the
balance to stabilize.
Open the lid and CAREFULLY
place the object on the center of the pan.
Close the lid and wait for the digital readout to stabilize
('*').
Record the mass of the object DIRECTLY into
your laboratory notebook.
Open the lid and remove the object from the weighing pan.
To determine
the mass of an object by difference:
Check that the balance is on, that the lid is closed, and it is
properly zeroed. An '*' will be in the upper left hand corner of
the display, and the mass should read as 0.000 g. If you do not
see both of these, push the 'Tare' button and wait 5-10 seconds for the
balance to stabilize.
Open the lid and CAREFULLY
place the container on the center of the
pan.
Close the lid and wait for the digital readout to stabilize
('*').
Record the mass of the container DIRECTLY into
your laboratory notebook.
Open the lid and remove the container from the weighing pan.
Place the chemical into the container.
Place the container with the chemical on the weighing pan.
Close the lid and wait for the digital readout to stabilize
('*').
Record the mass of the container containing the chemical DIRECTLY
into your laboratory notebook.
Open the lid and remove the container.
Determine the mass of the chemical by subtracting the two masses.
