NEVER point the mouth of a test tube or Erlenmeyer flask at
yourself or another person! ALWAYS direct the mouth away from
Sometimes, heat is evolved when substances are mixed. Always
have a place to set a vessel that gets too hot to handle. An easily
available test tube rack and an area cleared of notebooks, glassware,
and other items is important in the laboratory. Why?
In addition, do not set glassware or test tube racks near the edge
of the laboratory bench, where they may easily be inadvertantly bumped.
Mixing two liquids
When mixing two liquids, the techniques and apparatus used
depend upon the total volume of liquid to be mixed. Small samples
(less than 10 mL) should be mixed in a test tube, and larger samples
should be mixed in a beaker. Why?
Video: How to mix small volumes
in a test tube via striking ( 1.85 M )
If the two liquids are water and an acid, always add the acid
to the water slowly. Never add the water to the acid.
Video: Result of adding water
to acid(!) ( 1.43 M )
Mixing a solid and a liquid
Add the desired amount of solid to either a beaker or an Erlenmeyer
flask (use the Erlenmeyer flask if a gas may be evolved). Add
the liquid to the vessel, and mix by stirring with a glass rod
if using a beaker or by swirling if using an Erlenmeyer. Alternately,
a magnetic stir bar and a stirring plate may be used.
If the solid will not dissolve, gentle heating with the hotplate
may be necessary (see the Hotplate/Magnetic Stirrer module).
Be sure to use solvent to rinse any solute from the glass
rod before removing it from the solution.
Copyright © 1995-1996 NT Curriculum Project, UW-Madison