Balance
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A Description
The laboratory balance is used to measure masses. When using
a balance, the most important parts are the balance pan, the draft
shield, and the digital display.
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What does the "g" on the digital display stand for?
Answer
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Using the Draft Shield
Check that the balance pan is clean and dry. Place the draft
shield over the balance pan. The cover should also be placed on
the draft shield between uses of the balance.
Why use a draft shield?
Video: Using the Draft Shield ( 3.62 M )
Choosing a Weighing Vessel
NEVER WEIGH A SAMPLE DIRECTLY ON THE BALANCE PAN!
Choose a weighing vessel that can be used in subsequent steps
of the experiment. A beaker may be appropriate for weighing liquids
to be heated, and an Erlenmeyer flask may be appropriate for weighing
substances that will generate a gas in subsequent reactions. A
plastic weighing boat can only be used for weighing solids.
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Weighing boat pouring
substance into flask |
Beaker heated on a hot plate |
Erlenmeyer flask on hot plate |
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A laboratory procedure instructs you to weigh
approximately 0.3 g copper and cover it with 10 mL of 6 M nitric
acid. You know that the reaction between copper and nitric acid
produces nitrogen dioxide, a toxic gas. Which vessel will you
choose to weigh the copper? Answer
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Taring and Taking Readings
Sometimes when nothing is on the balance pan, the mass display
will show a non-zero reading. Taring is used to set the mass display
to zero. Once the balance has been tared, the mass of any object set
on the balance pan will be displayed on the digital readout.
The two types of taring techniques commonly used are automatic
and manual taring.
Video: Automatic taring ( 6.08 M ) Text description
Video: Manual taring ( 7.86 M ) Text description
Cleaning Up
If more than the desired amount of material is weighed, place
the excess material in an appropriate waste container. Never return
excess or unused chemicals to their original containers!
Video: Put excess chemicals in waste
containers ( 1.89 M )
Before leaving the balance, clean up the area. Use a brush
to clean all solids from the balance pan, and wipe up any liquids. Wear gloves while cleaning if a material may be hazardous.
Also clean the area around the balance. Dispose of any excess
or unused chemicals in an appropriate waste container.
Video: Cleaning balance area ( 2.94 M )
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You have spilled NaCl around the balance area.
When you clean it up, where should you put it?
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A. Solid waste container
B. Garbage can
C. Organic waste carboy
D. Into your reaction flask, since it's one of the reactants
E. Back into the NaCl reagent bottle
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Common Problems
Miscellaneous Exercises
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Will this sample give an accurate mass reading? Why or why not?
Answer
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Video ( 3.07 M ) |
What did this student do incorrectly? Answer |
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Copyright © 1995-1996 NT Curriculum Project, UW-Madison
