We also do a version of this experiment using cotton swabs with wooden sticks and wet the cotton tips with DI water and roll in solid salts (knowns and unknowns) in the wells of a dropping plate. The swabs pick up enough crystals to give definitive colors for each salt, and it is easy, quick and safe to repeat if the students are unsure of which salt matches their unknown. We keep a beaker of tap water handy to each set-up to quench the swabs when the sticks catch on fire. No flammable liquids in the room. No long prep time either.
Lead Chemistry Instructor
Western Technical College
400 7th St. N.
LaCrosse, WI 54601
"It's better to be careful 100 times, than to be killed once."
We do this experiment in General CHEM Lab with solid salts and wooden sticks soaked in DI water. A few crystals are picked up on the stick and placed into the flame of a burner. No flammable solvents in the room.
Sheila Kennedy, C.H.O.
Safety Coordinator | Teaching Laboratories
UCSD Chemistry & Biochemistry |MC 0303
Office: (858) 534-0221 | Fax: (858) 534-7687
From: DCHAS-L Discussion List [mailto:dchas-l**At_Symbol_Here**MED.CORNELL.EDU]
On Behalf Of Patricia Redden
Sent: Tuesday, January 07, 2014 11:13 AM
Subject: [DCHAS-L] Rainbow exp in gen chem lab book
I went to my office today, even though I planned to stay home and keep warm. However, a burst pipe in my lab flooded not only that lab but the two immediately below it. No instrumentation there, luckily, but because I was in the office I picked up the lab book I brought to CCS attention in the fall because of real concern about the procedures it contained. The title is Laboratory Manual for Chemistry: A Molecular Approach, by Tro; authors of the lab manual are Vincent and Livingston from the University of Alabama. It's a 3rd edition published by Pearson.
In the directions for Exp 12, Flame Tests: Flames and Smoke Bombs, the author states that the procedure given generates "more exciting and/or more spectacular colored flames" than the traditional method of using a wire loop with a "soluble form" of the element. The procedure for the flame tests in Part A is here given verbatim. Italics are as given in the manual.
"Obtain 5 watch glasses. Set them on the bench several inches apart. Label them Na, K, Li, Cu and Sr. Weigh out 0.1 g of NaCl, KCl, LiCl, CuCl2 [sorry, I can't find a way to do subscripts in my mail program], and SrCl2. Place each solid in the appropriately labeled watch glass. Obtain a squirt bottle containing methanol. Add methanol to a watch glass until it is nearly filled. Return the methanol bottle to its original location. With a long-handled all-purpose lighter, light the methanol in the watch glass; make sure the watch glass is well removed from any other sources of methanol. Watch the resulting flame. What color appears in the flame? Blow out the flame before the methanol is completely consumed. Repeat this procedure for the remaining metal salts. Watch the potassium chloride carefully. (The lights may need to be dimmed to see the resulting color in this case.)
"The leftover solutions and mixtures of metal chloride salts and methanol must be disposed of in appropriate waste containers. Your instructor will provide details."
Note that the safety notes require safety goggles and state that "This experiment involves the use of open flames and may involve the use of volatile and flammable chemicals." This lab is not a demo - it is designed for each student in the lab to conduct!
I spoke to the reps for Pearson at the expo, and in particular the person directly responsible for this lab book. (This is only one of the problems I found from a safety angle in the book, by the way.) Since it was written by authors from a major university, the rep was totally unconcerned about the lack of safety in the book.
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