Safety & Lab Tips

General Safety Techniques

Safe lab work requires attention to three potential ‘targets’: yourself, other people inside the lab, and the outside world. This page discusses each target and offers suggestions for performing specific lab operations more safely (see also Padias p. 1-3 for brief instructions).

Protecting the outside world. The most obvious step for protecting the outside world is to dispose of all materials properly (see Disposal). Another, less obvious step is avoid lab operations that pollute the environment.

Unfortunately, a total ban on lab pollution is hard to achieve. Volatile solvents, even when used in fume hoods, pollute the atmosphere. Compounds that go down the sink ultimately pollute streams and soil.

A perfectly non-polluting experiment may be impossible, but this does not make us less responsible for the outcome. If we cannot eliminate unsafe chemical emissions from the Chem 201/202 lab, we should at least try to minimize them. This principle has guided the selection and design of our experiments, but more needs to be done. You must also play your part and make sure that all chemicals within your control are disposed of properly.

Protecting yourself and other people inside the lab. There are three things you can do to keep yourself and others safe while working in the lab:

  • Set up barriers
    • Wear goggles at all times
    • Wear protective clothing and shoes at all times (no bare toes, no bare tummies, no bare shoulders, etc.)
    • Perform all operations in a fume hood and watch your material through the hood window
  • Keep your distance
    • Keep your face at least 2 feet from your materials and apparatus
    • Never hold an apparatus or compound over your face/head
    • Never point the opening in a flask or test tube at someone else
  • Avoid dangerous operations

‘Avoid dangerous operations’ is an extremely important principle, but how does it work? How do beginners, in particular, recognize a dangerous operation? The following list provides safety tips organized by the type of operation.

Measuring compounds

  • Measure solids on a balance
    • Put clean weighing paper (or weighing boat) on balance and press “Tare”
    • Add solids by spatula until the desired weight is approximated
    • Do not return contaminated compounds to reagent bottle
    • Clean up spills around the balance
  • Measure liquids by volume in a graduated cylinder in a fume hood
    • Solutions: Calculate #moles from liquid volume and solution concentration
    • Pure liquids: Calculate #moles from liquid volume, density, and molecular weight
  • Useful approximations
    • 20 drops from disposable pipet = 1 mL
    • 1 pipet load = 1 mL (assumes partially filled disposable pipet)

Transferring compounds

  • Perform all transfers (especially liquids) in a fume hood
  • Contaminated ground glass joints do not work properly. Keep them clean
    • Use a funnel to place compounds in a round bottom flask or separatory funnel
    • Use a wide-necked, short stem (powder) funnel for solids
  • Never (NEVER!) pipet liquids by mouth

Heating compounds

  • Organic compounds produce flammable vapors and can be ignited by sparks from an electronic heater or flame
    • Use a ceramic heater that matches or exceeds your flask size
    • Plug the heater into a voltage controller and never the wall outlet
    • Set the heater on top of a lab jack so it can be quickly removed in an emergency
    • Start off with the heater and container touching (otherwise the heater may become too hot)
  • Spark-producing heaters can be used to heat non-flammable compounds
    • Use a hot plate/stirrer to heat aqueous solutions
    • Use a heat gun to dry clean glassware, but never use a heat gun on flammable compounds or plastic (melts)
  • Never make an open flame in our lab
  • Never heat glassware to dryness (except to dry clean glassware with a heat gun)
    • If glassware becomes dry by accident, turn off heat and allow glassware to cool on its own (remove heater if practical)
  • Never heat a closed system (even partially evacuated closed systems)
  • Turn off heaters as soon as you are finished with them

Applying a vacuum

  • Unsafe evacuation procedures can lead to explosions (heating a partially evacuated closed system) or implosions (collapse of thin-walled or damaged glassware). Although they sound different, they look the same: dangerous glass shards and chemicals spray all over the lab
  • Use heavy-wall rubber tubing for vacuum filtration and vacuum distillation
    • Thin-wall rubber tubing and tygon (plastic) tubing tend to collapse leaving a partially evacuated closed system
  • Use heavy-wall unscratched glassware for vacuum filtration and vacuum distillation
    • Never evacuate an Erlenmeyer flask (thin glass walls makes flask liable to implode)
  • Water aspirators – set water flow to its maximum rate to create a strong vacuum

Water hoses

  • Use thin-wall rubber or Tygon (plastic) hoses
  • Turn off water when you do not need it (and before you leave the lab)
  • Condensers – use a steady trickle of water to keep a condenser cold
    • Use metal springs to lock hoses on condensers
    • Insert the drain hose at least a couple of inches into the sink to anchor it there
  • Aspirators – use the maximum water flow to make the strongest vacuum


  • Cleaning options
    • Traces of organic compounds – rinse with acetone (send liquid into organic waste container)
    • Otherwise – wash with brush, soap, and water; rinse with deionized water; hang on draining rack (make sure you put all of your glassware, wet or dry, in your desk at the end of each lab period)
    • Never dry glassware with compressed air. Compressed air pipes contain an ugly assortment of microscopic contaminants (water, oil, dust, etc.) that spew out in the air stream
  • Drying options (use these when an experiment calls for clean, dry glassware)
    • If glassware is already clean – dry glassware with heat gun starting from the bottom
    • If glassware is dirty – clean (see above), rinse with acetone, and then rinse again with a small amount of the dry solvent that will be used (send acetone and solvent rinses into organic waste container)
    • Never dry glassware with compressed air. Compressed air pipes contain an ugly assortment of microscopic contaminants (water, oil, dust, etc.) that spew out in the air stream
  • Fractionating column
    • Normally no cleaning is required (we use this apparatus for only one experiment and this use does not normally contaminate the column)
    • If cleaning is required, rinse with acetone (send rinses into organic waste container)
  • Separatory funnels
    • Do not dry a separatory funnel (normal usage involves pouring water into the funnel anyway)
    • Disassemble the funnel before storing it in your lab bench, otherwise the pieces may stick together
  • Assembly – disassembly of multi-piece apparatus
    • Assemble by clamping the bottom piece (usually a round bottom flask) to the monkey bars. Other pieces should rest on top of this one, and can be secured with additional clamps (either loose clamps to monkey bars or plastic clamps). Never dangle the lowest piece from the other apparatus
    • As a rule, do not place grease on ground glass joints. The grease tends to dissolve in your materials and contaminate them (exception: a light layer of silicone grease should be applied to glass stopcocks)
    • Do not grease Teflon surfaces
    • Disassemble all apparatus before storing it, otherwise the pieces may stick together