Q220: Prep Notes

Introduction

Salt slurries in petri dishes with methanol are ignited and characteristic colors for various metals are observed.
Colors of emission spectra are due to loosely-bound valence electrons being excited in a flame and dropping back down while emitting light.

Supplies

Short List

  •   Petri dishes with lids
  •   Marker
  •   Wash bottle with distilled water
  •   Matches
  •   Goggles

Chemicals

  •   Various metals (8 types)
  •   Wash bottle with methanol

Prior to Lecture  (prep time ~ ? min.)

  1. Add 1-2g of each salt to be displayed in a petri dish with lid.  Label both dish and lid with marker.  Suggested metals are: Li (red), Ba (yellow), Ca (red and blue), Cu (green), K (lavender), Sr (orange-red), Na (orange), and Ni (blue and sparking).  Allow salts to dry before storing petri dishes.
  2. Assemble the following:
  •   Fire extinguisher
  •   Wash bottle with distilled water
  •   Matches
  •   Wash bottle with methanol

To Conduct Demonstration

  1. Add a few mL of distilled water to each metal salt in its petri dish and mix to form  a slurry.
  2. Pour methanol into each dish to a depth of ½”.
  3. Carefully ignite the methanol with a match.  After 15-60 sec., colors should appear.  If the flame burns out, DO NOT add more methanol - this is a significant fire hazard!

Demo Time: ~? minutes

Safety 

Salts may spatter and eye protection should be worm.  Place dishes on heat-proof surface.  Dishes remain hot after the flame goes out and should be handled with care. The methanol bottle should be kept well away from any flames, and more should NOT be added in the event the flames go out. See this article on accidents that have occurred with this demo: https://cenblog.org/the-safety-zone/2014/09/denver-student-hit-in-chest-with-jet-of-flaming-methanol/