This document provides instructions and background information for three chemistry demonstrations: making ice cream without an ice cream maker, using an espresso machine to illustrate boiling and condensation, and examining the chemical reactions that take place with burning candles. The ice cream demonstration illustrates colligative properties and freezing point depression. The espresso machine shows boiling and the phases of water. The candle demonstration examines the combustion reaction and soot formation through observation of the flame and smoke. Context is provided for why these particular demonstrations were chosen, including to show students chemistry is part of everyday life.

1. Three Demos for Chemistry Class
Don’t Try this at home
James T. Stemmle, PhD
Hagerstown Community College
AFACCT 2012, Montgomery College – Rockville, session 6.13, 6 Jan 2012
jstemmle@comcast.net

2. 1) Ice Cream
• Freezing point depression
Tf = m Kf
• Where Kf = 1.86 oC/m,
m = molality, i.e., moles/kg solvent
Which is an example of Colligative properties,
namely properties dependent only on the
number of solute particles and not on the nature
of the solute.

3. Items needed
• 1 lg ziplock baggie
• 1 sm ziplock baggie
• Ice c. 1 lb
• Salt c. ¼ lb
• ~ 1/3 c water
And maybe:
• Small dish
• Plastic spoons
• Thermometer
• Watering can/water bottle

4. Some pertinent facts and calculations
• Serving temp of Ice cream: -16oC
• Corresponding molality: m = 16oC/1.86oC/m = 8.602m
• Molarity for NaCl ions: 4.3 m
• MW of NaCl: 58.45 g/mol (Na: 23. Cl: 35.45)
• Grams of NaCl: 4.3 moles x 58.45 g/m = 251 g NaCl/kg
water. So, about one fourth the mass of ice/water.
• Solubility in cold water: 35.7g/100g = 357 g/Kg H20
• 357/58.45 g/mol = 6.108 moles/Kg, i.e., 6.108 m
• Molarity of ions: 12.208 molal
• Max FP depression = 12.2 m x 1.86oC/m = 22.7oC
• Density of NaCl = 2.165 g/ml

5. So, rule of thumb:
• By mass, 4 parts ice/water, 1 part salt, and
since density of salt is 2.156 g/ml, …
• By volume: 8 parts ice/water, 1 part salt.

6. Why Ice Cream?
• It could be used to illustrate colligative
properties with calculations and all.
• It’s fun. Students get something useful. The
product is actually delicious.
• It illustrates that chemistry is the context of
our lives.
• It is safe and can be done with common things
found around the house.
Acknowledgement: ICE and Ann Caldwell.

7. 2) Espresso
• Every morning I think hey this would make a
great demo
• And I actually use it
• It shows the chemistry hidden in ordinary
things. Hey, open your eyes. Pay attention.
• In particular, it illustrates what goes on in
boiling (evaporation) and condensation

8. Some stray facts
• Alton Brown (The food Channel Nerd: “Good
Eats” show) says none of the coffee makers on
the market use hot enough water.
• Espresso does not have an x. First syllable
pronounced Ess.
• My Mr. Coffee espresso machine was acquired for
$3 at a thrift store
• This particular machine is the favorite source of
steam for at least one established luthier. I
, myself have used it to repair a guitar. (Steam
softens glue. Is used to remove the neck.)

9. The Espresso Machine
• It’s a boiler with a steam outlet and a boiling
water outlet.
• The boiling water is forced out of the boiler by
steam pressure.

10. What do we observe?
• First bubbles, hissing sound
• Some water ejected
• Then louder sound. The peculiar espresso
sound mimicked on TV, but no bubbles.
• Finally hot bubbles.

11. Why Espresso Demo?
• Fits with distillation experiments. Also illustrates
phenomena occurring in Hydrogen and Oxygen
experiments. Namely contamination of first
bottle with initial head gases.
• Could be used to illustrate the scientific method.
To test powers of observation. In query based
teaching. How do we explain that bubbles come
first, then no bubbles, then bubbles again. What
is going on here?

12. 3) Candles
• What do you see?

13. The Chemical Equation
• 2 CnH2n+2 + (3n/2 + ½) O2 → 2n CO2 +(2n+1) H2O
• For example: n = 21
– C21H44 + 32 O2 → 21 CO2 + 22 H2O

14. Only the yellow part of the flame
absorbs light and casts a shadow
• primary soot particles have roughly the
composition (C3H)n, and each is actually made
up of several thousand carbon atoms. The
empirical formula suggests cyclic, highly
unsaturated, polycyclic aromatic structural
elements. The primary soot particles grow
through agglomeration, dehydration, and
coagulation to as much as a few million carbon
atoms [9]. The resulting large soot particles
begin in Zone IV at temperatures above 1200 °C
to glow.
• yellow candlelight is a direct result not of a
chemical reaction, but rather of solid soot
particles thermally transforming energy into
light

15. Factoids
• All three phases are present in the wax fuel:
solid, liquid gas
• The flame produces no visible smoke.
• A disturbed flame produces sooty, black
smoke made of solid carbon.
• When extinguished, a candle produces white
smoke that smells like wax

16. Temperature Profile

17. The Faraday Lectures
• Royal Academy Christmas Lectures for young
People, 1860-1861. (during our Civil war)
(Available for free download from
www.gutenberg.org/etest/14474)

18. Excerpts
• And now, my boys and girls, I must first tell you of what candles are
made. Some are great curiosities. I have here some bits of timber,
branches of trees particularly famous for their burning. And here
you see a piece of that very curious substance taken out of some of
the bogs in Ireland, called candle-wood.
• A candle, you know, is not now a greasy thing like an ordinary tallow
candle, but a clean thing, and you may almost scrape off and
pulverise the drops which fall from it without soiling anything.
• There is not a law under which any part of this universe is governed
which does not come into play, and is touched upon in these
phenomena. There is no better, there is no more open door by
which you can enter into the study of natural philosophy, than by
considering the physical phenomena of a candle

19. Greatest Technological Development
of the 19th Century
• Per NY Times article, approaching the year
1900.
• Three guesses …
• Why yes we have come a great distance

20. So now the demonstration
• Waxy smoke
• Soot deposit
• Round scorch marks
• Parlor trick: re-ignighting a candle w/o
touching the wick

21. Lab Experiment
• We know the heat of combustion of a candle,
namely 43.3 ± 0.3 kJ/g
• We know how to determine the amount of heat
getting into a container of water, namely, Q = m C
ΔT
• So, we can answer a question like: What is the
heating efficiency of a candle?
• Or several other questions:
– Affect of wire gauze
– Affect of container, e.g., glass vs tin can.
– Affect of distance from the flame

22. Steps
• Weigh the aluminum can
• .Weigh candle
• .Measure 50 ml water into can
• .Measure initial temp
• .Light candle
• .When temperature has risen ~ 50o measure final temp. Note: candle cannot be
allowed to drip its liquid candle wax. If this is about to happen, gently extinguish
the candle and measure the temperature immediately, even if the ÄT is not 50o.
• .Gently Extinguish candle (do not provoke loss of liquid candle wax. Try suffocating
the flame with another small tin can.
• .Allow candle to cool
• .Weigh candle
• .Calculate the heat that transferred to water Qw = m SH ÄT where m = mass of
water @ 1 g/ml, SH = specific heat = 4.184 J/g oC. ÄT = change in temp = T2 - T1
• .Calculate the total heat given off by the candle: heat = Qc = (mass lost by the
candle)(43.8 kJ/g) = m(43.8 kJ/g)
• .Calculate the percent efficiency = Qw/Qc x 100

23. Data Sheet
1. Mass of aluminum can ______________________ g
2. Initial mass of candle: ______________________ g
3. Volume of water in the can: ____________________ mL
4. Mass of the water in the can/ beaker: ____________________ g
5. Initial temperature of the water _________________ oC
6. Time lapse to reach final temp:_________________________ sec

24. Data Sheet, cont.
7. Final Temperature of the water: _________ oC
8. Final mass of the candle: ________________ g
9. Mass lost by the candle: (2) - (8) __________ g
10. Increase in temp of the water: (7) - (5) ____ oC
11. Heat that flowed into the water: ___________ J
Qw = m SH (T2-T1) = (4) x 4.184 J/goC x (10)
12. Heat given off by the candle: ___________ kJ (9) x 43.8 kJ/g
13. Heating efficiency: ____________________% (11)/(12) x 100

25. Why these?
Some myths
•Chemistry is a forbidding scary course
•Chemistry is what happens in a lab
•Chemistry is no fun
•Chemistry is arcane – consisting of secret
knowledge known to only a few
•You need a lot of math to understand
chemistry

26. Facts. OK more myths. Better ones
• Chemistry is the context of our lives.
• Everything is chemical. OK everything at least
has a chemical dimension
• Chemistry is the basis for the way we live
• Food, materials, energy, shelter all have their
basis in chemistry.
• For a person to be comfortable in his or her
own skin and on this planet, he or she needs
to know chemistry

27. References
• “Chemistry of the Christmas Candle” by Klaus
Roth, Chemie in unserer Zeit, 2 Novb 2011,
and online at
http://www.chemistryviews.org/details/ezine/1369631/Chem
istry_of_the_Christmas_Candle__Part_1.html
• “A Candle in the Wind”, by Robert J. Eierman,
Journal of Chemical Education, vol 85, No. 4,
April 2008