Instant, Instant Coffee
Reactions of Calcium Carbide—Combustion of Acetylene
SCIENTIFIC
Introduction
Present a real world problem that requires the use of gas laws, thermochemistry, and stoichiometry—Oh, ya—and blow
something up!
Materials
Calcium carbide, CaC2, 10 g Butane safety lighter
Instant coffee, ½ teaspoon
Plastic pitcher, 1- or 2-quart, with lid
Safety Precautions
Calcium carbide is corrosive to eyes and skin; exposure to water or moisture evolves flammable acetylene gas. The reaction in this demonstration releases flammable acetylene gas. The reaction may produce a loud explosion. Wear hearing protection and warn the audience to
cup their ears. The lid of the pitcher will fly off violently. The acetylene may continue to burn after the explosion. Have a fiber pad or fire
extinguisher ready to smother or put out the fire. Perform this demonstration in an operating fume hood or a well-ventilated room. Wear
chemical splash goggles, chemical-resistant gloves, and a chemical-resistant apron. Please review current Material Safety Data Sheets for
additional safety, handling, and disposal information.
Preparation
1. Sparker set up
Melt or cut a hole in the middle of the back of the plastic pitcher the size of the flame
end of a butane safety lighter. Insert the butane safety lighter. Use this as a sparker
(see Figure 1). If the butane safety lighter is out of fuel, it still works for this demonstration.
2. Calcium carbide “Instant Coffee” sample
a. Mass about 1.2 g of calcium carbide on a 0.1-g precision balance.
b. Add this to a tablespoon of instant coffee.
c. Set the tablespoon on top of the open container of instant coffee.
d. Add 250 mL of tap water to the plastic pitcher.
e. Place the safety shield in front of the pitcher.
Figure 1.
Procedure
1. Add the tablespoon of “Instant Coffee” to the plastic pitcher. Place the lid on the pitcher.
2. Wait between 5 and 10 seconds, then spark the butane safety lighter.
3. Observe as the lid flies off the pitcher and flames shoot out the top.
Disposal
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures governing the disposal of laboratory waste. The reacted calcium carbide solution may be disposed of according Flinn Suggested
Disposal Method #10.
Tips
• Explain to the students that the coffee will be prepared in a special instant coffee pot with the lid closed. Depending
on the level of your students, you will have to decide how much help to give them on the calculations. AP students
© 2016 Flinn Scientific, Inc. All Rights Reserved.
Publication No. 91247
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Instant, Instant Coffee continued
will generally get the answers. With luck, other students will determine that oxygen is the limiting reagent. It works
best to give them a day to do the calculations.
• Waiting 5 to 10 seconds before igniting the acetylene is the critical part. If you wait too long. you will drive most of the
oxygen out of the pot and too short a wait will not have sufficient acetylene produced. Practice to see the best wait time
for your system. When you spark the acetylene the lid will fly off the pot and flames will shoot out the top of the pot.
• Students will want to do the reaction again. Ask if they want to add more CaC2. They will always want more. (In spite of
the stoichiometry) Run the reaction with twice as much calcium carbide. The pot will not explode because much of the
oxygen will be used up.
Discussion
Instant Coffee is not really instant unless you have a source of instant hot water. To make “truly” instant coffee we need to add
something to the coffee that will heat the water as the coffee dissolves. How about calcium carbide? It reacts with water to
release acetylene which is an exothermic process and the acetylene can then be burned to release even more heat. This energy
will instantly heat the coffee! The question is, “How much CaC2 can be mixed with a teaspoon of coffee to get the right amount
of heat?”
The two equations for the reactions are:
CaC2(s) + 2H2O(l) → C2H2(g) + Ca(OH)2(aq)
Equation 1
2C2H2 + 5O2(g) → 2H2O(g) + 2CO2(g)
Equation 2
Calculations
volume of air in pot
900 mL
atm pressure
754 mm Hg
room temp 25°
% O2 in air
21%
Pressure of dry air Pdr air = Patm – Pwater = 754-24 = 730 mm
PO2 = .21 (.730 mm) = 153 mm
moles O2 = PV/RT = 153 (.900)/62.5(298) = .00741 mol O2
grams CaC2 = [.00741 mol O2(2 mol CaC22/5 mol O2) (64.1 g/mol)] = 0.19 g
Connecting to the National Standards
This laboratory activity relates to the following National Science Education Standards (1996):
Unifying Concepts and Processes: Grades K–12
Constancy, change, and measurement
Content Standards: Grades 9–12
Content Standard B: Physical Science, structure and properties of matter, chemical reactions, interactions of energy
and matter
Reference
John C. Schaefer, Parks College
Flinn Scientific—Teaching Chemistry™ eLearning Video Series
A video of the Instant, Instant Coffee activity, presented by Bob Lewis, is available in Reactions of Calcium Carbide—Combustion of
Acetylene, part of the Flinn Scientific—Teaching Chemistry eLearning Video Series.
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© 2016 Flinn Scientific, Inc. All Rights Reserved.
Instant, Instant Coffee continued
Materials for Instant, Instant Coffee are available from Flinn Scientific, Inc.
Catalog No.
C0346
AP8960
Description
Calcium Carbide, 100 g
Butane Safety Lighter
Consult your Flinn Scientific Catalog/Reference Manual for current prices.
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© 2016 Flinn Scientific, Inc. All Rights Reserved.