A Perfect Reaction (see all): You do not make errors in your
calculations, you do not need special equipment, you have clean, dry glassware,
and you do
not need to purify reactant, reagents or solvent.
A Nightmare Scenario (see all): You need to weigh four
different
reagents: a hygroscopic solid that gets liquidy in air,
0.05 mg of catalyst, a liquid that clogs syringes and must be distilled
immediately before
use, and your
precious reactant, which is heat and acid sensitive. The reaction must be done at
-30 C
under argon
using a complex glass apparatus, and requires three flasks for successive dropwise
addition
via cannula.
Locate a clean, dry flask, a stirbar, a septum and any other apparatus
necessary for the
procedure. Calculate the total milliters of solution, and use a flask with at
least twice that
capacity.
If the reaction is moisture or air sensitive, oven- or flame-dry the flask and
prepare to
run the experiment under an inert atmosphere.
Purify your reagents and solvents, if necessary.
Locate syringes and needles of appropriate size, if necessary.
Weigh your reactants, into your reaction flask, onto weighing paper, or into a
separate
flask (a pointy flask is useful for reagents that will be added in solvent).
Consult your procedure to see what is necessary. Do not mix anything yet, and do
not
weigh sensitive reagents until just before use.
Allow compounds from the refrigerator to warm to room temperature before
opening
them,
to avoid undue exposure to air.
To weigh a liquid:
Using the density of the liquid, calculate the volume of liquid and use a
syringe.
Weigh an empty syringe, fill the syringe, and weigh again.
If the liquid is in a flask, and you only need a fraction of it, try this:
if you have 90 mg in the flask, and you need 30 mg, dissolve the material in 3 mL
of solvent,
and remove 1 mL. You can remove the solvent to check the weight. This method is
more
accurate
than you might think.
For small amounts of viscous liquids, weigh an empty pipette, dip the tip
in the substance,and weigh again. This is not a generally useful method, but good
sometimes.