If stirring stops during a reaction, all bets are off. It is very important to stir continuously throughout an experiment.
If you experience problems stirring, here are some things to try: (replaces the troubleshooting the reaction link)
Move the bottom of the flask closer to the stir plate.
Use a bigger stir bar.
Use a larger or more powerful stir plate (not all plates are created equal).
If your stir bar gets stuck somehow, pick up the flask and swirl it until the bar is free, or pry it free with a pipette or spatula. These kinds of reactions require constant surveillance. If you are having this kind of problem, you might want to consider using a mechanical stirring apparatus.
If your reaction is very large, a stir bar may not mix it efficiently. It might work better if you used a mechanical stirring apparatus.
Remember, if your reaction is heterogeneous, it must be stirred very vigorously to ensure efficient mixing.
Cylindrical:Long and thin bars that are excellent
for Erlenmeyer flasks, but may spin irregularly in a
round-bottom. The short cylindrical bars sometimes fit
in a round-bottom and spin fine.
Football: Bars shaped to fit in a round-bottom flask.
Normally available for
25 mL flasks and larger.
Fleas: Very tiny cylindrical bars good for 10 mL
or smaller flasks, vials or test tubes.
When a stirbar simply does not do the job,
mechanical stirring is necessary. An
overhead stirring apparatus is typically employed.
Situations when overhead stirring may be required:
high viscosity solutions, large
scale reactions, or in heterogeneous reactions
when a stirbar becomes mired in
gunky, gooey, or otherwise insoluble material.
Syringes and Needles
Disposable syringes: These are excellent for
addition of 1-50 mL of solvents
and most non-corrosive, neutral reagents.
Disposable syringes do not have Luer
locks, so be aware that needles can pop off easily.
Glass syringes: Good for working with reactive
reagents, but they are easily jammed.
Gastight syringes: For precision measurements
and dangerous or sensitive reagents.
Microliter syringes: The only way to measure
small volumes of reagents. The
10 to 500 microliter sizes are commonly necessary
for synthetic experiments.
Either gastight syringes or glass syringes with a Teflon plunger are available.
Needles: Disposable needles are can be used
when their shortness is not a problem. Three- and six-inch
flexible metal needles are best for syringing
liquids through septa or Sure-Seal caps.
Gauge indicates the width of the
needle opening: 16 gauge is the widest commonly used,
and 22 gauge the narrowest.
Luer lock: A connection found on glass or
gastight syringes that locks the
needle in place when you twist. Luer lock-tubing
connections are available, and
can be useful for some applications involving transfer of gases.
Cannula: A needle with two points. It is used to
transfer solution from one
vessel directly into another.
Synthetic organic experiments are conducted at temperatures ranging from -90
degrees to 200 degrees Celcius. It is important to know how to achieve and
maintain the correct temperature for a reaction, especially over long time
periods. Temperature should be monitored with a low-temperature alcohol
Low Temperature Cooling Baths
Cryocool: If you have access to one, a cryocool
can maintain a reaction at a
set temperature (typically -40 to 20 degrees) for a long period of time.
Hot plate/oil bath apparatus with internal temperature control.
Solvent reflux: temperature will be the boiling temperature of the solvent.
Oil bath: Mineral oil polymerizes at ~150 degrees; for higher temperatures
switch to silicone oil or a heating mantle with sand (see below).
Heating mantle full of sand controlled by a Variac.
Sand is less messy than oil and high temperatures are
easy to attain. Put a thermometer in the sand and
then experiment with the Variac until you achieve the correct temperature.
Hot plate/water bath. Sometimes convenient for gentle heating (35-80