Mixing

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NEVER point the mouth of a test tube or Erlenmeyer flask at yourself or another person! ALWAYS direct the mouth away from people!

CORRECT		WRONG!!!

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.

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 )

Small volumes: Text description

Large volumes: Text description

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 )

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.

Related modules: Hotplate/Magnetic Stirrer