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 as volumes.
  • Generally masses can be measured more accurately than volumes.

This first experiment emphasizes the use of balances.

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SYLLABUS

Balances can be classified in several different ways.

  1. Precision of measurement.
  2. Mode of operation.

In this course, you will use four different types of balances:

Triple Beam Balance

  1. Use for "crude" weighings.
  2. This is a very sturdy balance. Never-the-less, clean up any spills!
  3. Reset weights to 0.00  when finished.
  4. At best this will weigh to .01 g.

Electronic Balances

  1. State of the art balances.
  2. Object to be weighed is counterbalances by a magnetic field generaled by an electrical current.
  3. In General Chemistry Laboratory, use only when allowed 
  4. These are fast.
  5. These are accurate.
  6. These are almost "idiot proof" !
  7. They are frequently more expensive than mechanical balances.
  8. In this course these will be used only for special experiments.
    In industry, where time is money, they are used almost exclusively.

Mechanical Analytical Balance.

  1. Obsolete!!   Used only in special experiments.
  2. Works like a teeter tauter, more or less!
  3. Always shut off the balance before putting anything on or off an mechanical analytical balance.
  4. Never lean on the bench when using an analytical balance.
  5. Treat the balance gently. It is very accurate but also sensitive and somewhat fragile.
  6. Before you leave an Analytical balance, make sure it is shut off and spotlessly clean!

RWK 2004