The Battle of the Buzzer
Overall Goal
During this demonstration the students will learn that ions have the ability to conduct
electricity when dissolved in water and that substances with this ability are called
electrolytes. Students will also learn about acid and base reactions as well as the strength
of electrolytes. This demonstration may be used in the context of a lesson involving any
or all of these topics.
Background Information
Since this demonstration involves a number of different concepts, it fits in with several
parts of the chemistry curriculum (acid/bases, ions, electrolytes). In order to fully
understand the demonstration and what makes it work, students must understand that that
ions dissociate in water and those dissociated ions have the ability to conduct electricity
within that solution.
Teachers must also ensure student understanding of acid and base reactions for a
complete understanding of this demonstration. When an acid and base react,
neutralization occurs producing a salt and water. The salt product then dissociates into
the component ions, which are then able to conduct electricity in solution.
Due to the prevalence of sports drinks containing electrolytes on the market today, this
demonstration might also be used in the living environment curriculum during the
nutrition unit or discussion of body chemistry.
Materials
6-V Battery (Large)
6-V Buzzer
Three small “jumper cables”
Six 100-mL beakers
Labels, marker
Deionized water (DI
Tap water
Six glass bottles with stoppers
1 M aqueous solutions of:
NaCl
HCl
Acetic Acid (CH3COOH)
Sodium hydroxide (NaOH)
Ammonia (NH3)
To prepare 1M aqueous solutions:
NaCl:
Fill a 100-mL graduated cylinder with approximately 50-mL DI. Add 5.8
g NaCl and stir to dissolve. Fill to 100 mL with DI and transfer to labeled,
glass-stoppered bottle.
Battle of the Buzzer
HCl:
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Fill a 100-mL graduated cylinder to about 50 mL with DI. Add 16.7 mL
6M HCl. Fill to 100 mL with DI. Transfer to labeled, glass stoppered
bottle.
Acetic Acid: Fill a 100-mL graduated cylinder with about 50 mL DI. Add 5.7 mL
glacial acetic acid (17.4 M) to the cylinder and fill to 100 mL with DI.
Transfer to labeled, glass-stoppered bottle.
NaOH:
In a small beaker, dissolve 4.0 g of NaOH pellets in approximately 50 mL
DI. Transfer to a 100-mL graduated cylinder, rinsing the sides of the
beaker into the cylinder with DI. Fill to 100 mL with DI. Transfer to a
labeled, glass-stoppered bottle.
NH3:
Fill a 100-mL graduated cylinder with 50 mL with DI. Add 6.9 mL
concentrated (14.5M) ammonia. Fill to 100 mL with DI. Transfer to a
labeled, glass-stoppered bottle.
Procedure
1. Set-up 8 250-mL beakers labeled in the following way: DI water, tap water,
NaCl, HCl, Acetic Acid, NaOH, NH3, and ?
2. Add approximately 100 mL DI water to the first beaker and 100 mL tap water to
the second beaker.
3. Transfer the contents of each of the 1M aqueous solutions from the glassstoppered bottles to the labeled 250-mL beakers. **Leave the beaker labeled ?
empty for now.**
4. Set up the buzzer as follows:
a. Connect one end of one jumper cable to the (+) battery terminal and one
end of another jumper cable to the (-) terminal.
b. Connect the loose end of one of the cables to one end of the buzzer.
c. Take a third jumper cable and connect it to the other end of the buzzer.
d. Clip a 2” piece of copper wire to each exposed wire. (This will prevent
corrosion of the “alligator” clips.)
e. The open circuit should look like this:
Buzzer
6V
Battery
Battle of the Buzzer
3
5. Place the copper wires in each of the solutions to test for conductivity. If you
don’t hear a loud “buzz”, bring wires close together (but not touching) to obtain a
signal.
6. Take some of the acetic acid and ammonia and combine in the last beaker (?).
Record your observation.
Hazards
Be cautious of connecting everything correctly. Make sure all clips are in
the right place and no corrosion is present.
Disposal
Dispose of diluted aqueous solutions in the sink.
Tips and Suggestions
Touch two pieces of copper wire to test the circuit before placing in solutions. If no
“buzz” is heard, re-check the connections and make sure the cables are connected to the
appropriate terminals.
Explanation of Why the Demonstration Works
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When ionic compounds are placed in water, they tend to dissociate. This means
that the parts of the compound separate in to their component positive or negative
ions. Different ionic compounds have different levels of dissociation in water,
some tend to dissociate completely while others dissociate only partially.
Solutions containing charged ions possess the ability to conduct electrical charge
and are called electrolytes.
Placing the open ends of an electrical circuit in an electrolytic solution causes
movement of electrical charge. The positive ions (ex. Na+) move through the
solution toward the negative terminal of the battery. The negative ions (ex. Cl-)
move through the solution toward the positive terminal of the battery.
The completion of the circuit causes the buzzer to “buzz”. The stronger the
electrolyte (or the higher concentrations of ions in solution) the louder the buzzer
will be. If a compound does not dissociate completely, the solution will be a
weak electrolyte able to conduct only a small amount of electricity and therefore
causing the buzzer only to produce a very weak sounding “buzz”.
Non-electrolytes are solutions that do not conduct electricity due to an absence of
charged ions. Deionized water and tap water do not contain any charged ions and
are therefore not electrolytes.
What happened in the mystery beaker?
o Both ammonia and acetic acid acted as very weak electrolytes when tested
on their own. When combined, however, the resulting solution was a
relatively strong electrolyte.
o Acids (acetic acid) are known as proton donors, while bases (ammonia)
are proton acceptors. When in solution, the acetic acid donates protons,
thus being left with an excess negative charge. The ammonia accepts this
Battle of the Buzzer
4
proton and therefore as an excess positive charge. This reaction looks like
this:
H2O
NH3 + CH3OOH  NH4+ + CH3COO-
o The positive and negatively charged ions are then able to conduct
electrical charge as described above.
Questions for Students:
1. Where have you heard the term “electrolytes” used before?
2. Why don’t you want to touch the two ends of wire together when you are testing
the solutions?
3. Draw a diagram showing what the contents of the “mystery” beaker looks like on
a molecular level.
Additional Suggestions
Use this as a discussion about sport drinks and their possible risks/benefits. Bring in
several different types of drinks and test quantity or strength of electrolytes in each.
modified by Amber Cost 2008