I recently tried an experiment in class that works well as a chemistry demonstration for Halloween. In fact, I recently performed it at our annual Halloween / National Chemistry Week chemistry demonstration show. The experiment is very easy to carry out. I call it “The Devil’s Milkshake”. Check it out in the video below.
Video 1: Devil's Milkshake, Tommy Technetium YouTube Channel, 10/26/19.
What a simple experiment! You simply drop calcium metal in water and ignite the resulting bubbles on fire with a lighter.1 Calcium metal reacts with water to form insoluble calcium hydroxide and hydrogen gas:
Ca(s) + H2O(l) à Ca(OH) 2(s) + H2(g) Equation 1
The bubbles that are formed contain hydrogen gas. When ignited, the hydrogen reacts with oxygen gas in the air to produce water and a lot of energy, producing the flame:
2 H2(g) + O2(g) à H2O(g) Equation 2
If you look closely, you will note that the flame is an orange-red color, indicative of a positive test for the element calcium. The combination of the milky white calcium hydroxide and red-orange flaming bubbles give this experiment the appearance of a flaming milkshake – The Devil’s Milkshake!
I recently posted this experiment on Twitter, and a few chemistry teachers mentioned some chemistry topics that relate to it. Andres Tretiakov mentioned the possibility of giving The Devil’s Milkshake a “strawberry flavor” by adding phenolphthalein2 to the water prior to adding the calcium metal. A small amount of the Ca(OH)2 that is formed dissolves, generating enough hydroxide ion to cause the phenolphthalein indicator to turn pink:
Ca(OH)2(s) à Ca2+(aq) + 2 OH-(aq) Ksp = [Ca2+][OH-]2 Equation 3
Meg Young mentioned to me that she often produces Ca(OH)2 by adding calcium metal to water (Equation 1). After filtering out the product Ca(OH)2, students use 0.10 M HCl to titrate the concentration of hydroxide remaining in the filtrate. Because from Equation 3 we see that [Ca2+] = ½[OH-], the hydroxide ion concentration can be used to find Ksp for Ca(OH)2:
Ksp = [Ca2+][OH-]2 = ½ [OH-][OH-]2 = ½ [OH-]3
When covering chemical periodicity, I add small samples of lithium, sodium, and potassium metal to water to show students how these three alkali metals react with water in a similar manner. After doing so, I add a sample of calcium to water and ask students how the reactivity of calcium, an alkaline earth metal, reacts differently with water than the alkali metals. The difference is that the production of a milky-white, insoluble product (calcium hydroxide) is of course only observed in the reaction of calcium with water.3
Please do let me know if you perform The Devil’s Milkshake for your students. If you do so, drop me a line and let me know what chemistry topics you related to the demonstration. HAPPY HALLOWEEN!
Read the follow-up to this post: Thermochemical Analysis of the Devil's Milkshake
- If you try this experiment, be sure to conduct the experiment in a fume hood. I use about 1 gram of calcium for every 100 grams of water. The bubbles are ignited with a grill lighter after letting them build up for a few seconds.
- Phenolphthalein is an acid-base indicator that is pink in a base and colorless in acid.
- You can see a quick video of this demonstration at the following link: https://twitter.com/pchemstud/status/1172501724575100928
For Laboratory Work: Please refer to the ACS Guidelines for Chemical Laboratory Safety in Secondary Schools (2016).
For Demonstrations: Please refer to the ACS Division of Chemical Education Safety Guidelines for Chemical Demonstrations.
Other Safety resources
RAMP: Recognize hazards; Assess the risks of hazards; Minimize the risks of hazards; Prepare for emergencies
Safety: Video Demonstration
Safety: Video Demonstration
Demonstration videos presented here are not meant as tools to teach chemical demonstration techniques. They are meant as a tool for classroom use. The demonstrations may present safety hazards or show phenomena that are difficult for an entire class to observe in a live demonstration.
Those performing the demonstrations shown in this video have been trained and adhere to best safety practices.
Anyone thinking about performing a chemistry demonstration should first read and then adhere to the ACS Safety Guidelines for Chemical Demonstrations (2016) These guidelines are also available at ChemEd X.