In the laboratory, one frequently makes measurements
such as weight, volume, temperature,
pH and absorbance of light.
- In measuring out a solid, the method of choice
is by mass (weight).
- Liquids are usually more conveniently measured
- Generally masses can
be measured more accurately than volumes.
This first experiment emphasizes the use of
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Balances can be classified in several different ways.
- Precision of measurement.
- Regular balances weigh to 1, .1, .01 or .001 g (1
- Analytical Balance,
to .0001 g . This is 0.1 mg.
- Semi-micro and micro balances, weigh to .00001 and .000001 g . This is .01
mg and .001 mg or 1mg (microgram).
- Mode of operation.
Uses weights to
balance object being weighed
electrical current to balance object
In this course, you will use four different types of
Triple Beam Balance
- Use for "crude" weighings.
- This is a very sturdy balance. Never-the-less, clean up any spills!
- Reset weights to 0.00 when finished.
- At best this will weigh to .01 g.
- State of the art balances.
- Object to be weighed is counterbalances by
a magnetic field generaled by an electrical current.
- In General Chemistry Laboratory, use only
- These are fast.
- These are accurate.
- These are almost "idiot
- They are frequently more expensive than mechanical balances.
- In this course these will be used only for special experiments.
In industry, where
time is money, they are used almost exclusively.
- Obsolete!! Used only in special
- Works like a teeter tauter, more or less!
- Always shut off the balance
before putting anything on or off an mechanical analytical balance.
- Never lean on the bench
when using an analytical balance.
- Treat the balance gently.
It is very accurate but also sensitive and somewhat fragile.
- Before you leave an Analytical balance, make sure it is
shut off and spotlessly
© RWK 2004