ELECTROLYTES AND NONELECTROLYTES
CHEM 110
Fall 2009
Name_____________________________________
Partner ___________________________________
Date ______________________
LEARNING OBJECTIVES: After completing this experiment, you should:
• Be able to use a conductivity meter to determine the conductivity of a substance.
• Make accurate predictions about the conductivity and electrolytic capacities of various
substances.
• Be able to write balanced dissolution reactions.
INTRODUCTION
Electrolytes are substances that must consist of charged particles called ions. They act as
electrolytes when the ions are free – usually in solution (or in liquid form) – to move around. The
ions, (+) cations, and (-) anions, are released and are free to move around when solids melt, or when
solids dissolve in solution. In this experiment, you will explore what types of compounds can
become electrolytes, what determines electrolyte strength, and how electrolytes are involved in the
conduction of electricity.
Discussion
Before we can discuss the properties that make a compound an electrolyte, we must first understand
something about the properties of electricity.
Electricity results from the movement of charged particles through a conductor. The charged
particles can be either electrons or ions (positive or negative). In some cases, both types of particles
can be involved. When the movement of electricity is through a metal, the electrons move from one
metal atom to another which serves as the means for carrying the charge in the electrical circuit. If a
liquid is included as part of the electric circuit, something must carry the charge through this solution
otherwise no electrical current will flow. When a non-electrolyte is added, no ions are formed in
solution and therefore, no current flows. If we instead put a light bulb in the electrical circuit** (a
beaker containing a polar solvent, such as water), it is possible to tell whether the compound being
added to the solvent is an electrolyte or a non-electrolyte by whether or not the light bulb lights up.
(**Note the set-up in the fume hood. The bulb assembly clamps to a ring stand.)
#5 Electrolytes and Nonelectrolytes
Rev F09AEM Fall 2009
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Determining the type of bonds present (Ionic, Polar Covalent or Nonpolar Covalent)
The percent ionic character of a bond is dependent on the differences in of the atoms present, and the
arrangement of these atoms in the molecule. When electronegativity differences are very large, a
bond is considered ionic; the electrons are completely transferred from one atom to another. When
the electronegativity difference is intermediate, the bond is considered polar covalent, and regions
of partial positive and partial negative charges are formed. When the electronegativity difference is
small then the molecule is considered nonpolar covalent. These trends can be estimated by the
position of the two atoms on the Periodic Table. When a compound is formed from elements that
are on opposite sides of the Periodic Table, such as from the s-block (metal) and the p-block
(nonmetal), that compound is typically ionic. When a compound is formed from elements all within
the p-block (all nonmetals), that compound is typically covalent. Hydrogen is often an exception – it
is often considered a nonmetal in bonding. Use the flowchart below to help you decide how to
classify individual molecules as ionic, polar covalent, or nonpolar covalent.
Polar covalent; contains ANY two
different non-metals bonded
together
(except C-H which are defined as
non-polar)
Yes, then the
compound is Ionic
Is a metal, or
NH4+ present?
No, then the compound
is Covalent
Non-polar covalent; contains
only C-H bonds, or all the same
element (e.g. O2)
Determining/Predicting Electrolyte Behavior
There are three types of electrolytes: strong, weak and non-electrolytes. A polar solvent is
necessary for an electrolyte to function:
1. Ionic compounds that are soluble are strong electrolytes. (Review solubility
rules). Ionic compounds that are insoluble are non-electrolytes.
2. Polar covalent compounds can be strong, weak or non-electrolytes. Most acids
have weak polar covalent bonds to the hydrogen, allowing water to pull the H+ off
of the molecule – thus acids will be an electrolyte – either strong or weak. (strong
acids are strong electrolytes, weak acids are weak electrolytes)
3. Non-polar covalent compounds form non-electrolytes.
For example, the ionic compound NaCl, when dissolved in a polar solvent, dissociates (splits apart)
completely to form sodium ions and chloride ions. These ions form because the electrostatic forces
present in the polar solvent help to stabilize the ions.
NaCl
polar
solvent
+
Na + Cl
Na +
δ0
-_
H
δ+
H
H
δ0
+ H
δ
Cl -
#5 Electrolytes and Nonelectrolytes
Rev F09AEM Fall 2009
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Ionic compounds are strong electrolytes in polar solvents if they are soluble; they form large
numbers of ions that can carry a large electrical current.
Polar covalent compounds may or may not form ions when dissolved in a polar solvent, depending
on the compound. Strong acids (polar covalent), (e.g. HNO3, H2SO4, HClO4, HCl, HBr, HI), when
dissolved in polar solvents, will form large numbers of ions and therefore form strong electrolytes
in water solution.
H2SO4 (aq) → 2 H+ (aq) + SO42- (aq)
100% ionized
Weak acids and weak bases (i.e., ammonia, carbonic acid) will only partially ionize (partially
dissociate or react to form ions) in a polar solvent. This partial dissociation is denoted by
“equilibrium” arrows: . Most of the compound remains in solution as non-ionized molecules.
Since there are very few ions in solution, only a small amount of the electrical current can flow. The
light bulb will light up, but only dimly, and is very dependent on the concentration of the
compounds. These compounds are weak electrolytes.
H2CO3 (aq)
HCO3-1 (aq) + H+1(aq)
99% molecules
1% ions
All nonpolar covalent and many weakly polar covalent compounds stay as molecules in solution
and do not form ions. They are unable to carry a charge and therefore are non-electrolytes.
If the solvent is nonpolar, it does not have the electrostatic forces (ion/dipole interactions) to
stabilize ions and so none form. Therefore, in a non-polar solvent, all compounds, which are added
to it, are non-electrolytes.
Also, a solvent may be very polar, but if there is no compound added to it to provide ions or support
the formation of ions, the solvent will not conduct electricity.
Summary of Bond Types
1. Ionic: Contains both metals and nonmetals, or the ammonium (NH4+) ion. Elements are
greatly separated on the Periodic Table.
2. Covalent: Contains only nonmetals (including hydrogen).
a. Polar Covalent: typically contains H-O or H-N bonds, strong acids. Elements have
intermediate separation on the periodic table (separated by two or three other
elements).
b. Nonpolar Covalent: typically contains lots of H-C bonds, or all atoms are the same
element. Elements are right next to each other on the Periodic Table.
#5 Electrolytes and Nonelectrolytes
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Summary of Electrolytes in Water
1. Strong electrolytes: a. soluble ionic compounds that dissociate (almost) completely into
ions.
b. strong bases (NaOH, LiOH, KOH, RbOH, CsOH, Ca(OH)2,
Ba(OH)2, and Sr(OH)2 dissociate almost completely into ions.
c. strong acids (polar covalent molecules) that dissociate almost
completely into ions.
2. Weak electrolytes: a. polar molecules that dissociate partially into ions, eg., weak acids,
weak bases.
b. slightly soluble salts that dissociate partially into ions.
3. Non-electrolytes:
a. nonpolar (covalent) compounds, that do not dissociate into ions.
b. very weakly polar compounds, that do not dissociate into ions.
Experimental
CAUTION: 1) It is extremely important to use safety goggles for this experiment and to use
caution in the handling of acids and bases.
2) It is also important to unplug the conductivity tester when cleaning the
electrodes or when not using the tester so that your body does not succeed in
completing the circuit which will result in a nice jolt of electricity coursing through
your body!
Procedure:
1. Your instructor will assign each group one or two solutions to set up.
2. Use the clamp on the tester to attach a conductivity tester to a ringstand.
***Caution: Do not plug in the conductivity tester!
3. Place the jar of sample solution under the electrodes of the conductivity tester, submerging the
electrodes in the solution.
4. Plug the tester into the bench electrical socket. Observe and record your results.
DO NOT TOUCH THE ELECTRODES WHEN THE APPARATUS IS PLUGGED
IN SINCE YOU WILL BE RECEIVING 110 VOLTS OF ELECTRICITY!
5. Once every sample is set up, walk around the classroom and observe all samples and record the
results.
6. To clean up, unplug the probe, remove the probe from the solution, rinse the electrodes with
distilled water, replace the lid on the jar of solution, and replace the jar on the prep bench.
#5 Electrolytes and Nonelectrolytes
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TABLE A-1
Substance tested
Conductivity
(yes or no)
Ions present?
(yes or no)
Electrolyte
strength
(strong, weak,
non)
Species present
(Identify all ions & molecules
that are present in the beaker)
2% Ethanol
(C2H5OH)
Distilled water
0.1 M HCl
0.2 M acetic acid
0.1 M NaOH
0.1 M H2SO4
0.1 M glucose
(C6H12O6)
0.1 M Ba(OH)2
0.1 M NaCl
0.1 M ammonia
(NH3)
For each solution that conducted electricity (the light bulb turned on) write a chemical equation
representing the dissociation behavior of each compound in water solution. If no dissociation occurs,
write NR for No Reaction. Include charges and phase labels. The first two are started for you as
an example of how to structure your equations.
Ethanol
C2H5OH (aq) →
Distilled water
H2O (l) 
Hydrochloric acid
HCl (aq) 
Acetic acid
CH3COOH (aq)
Sodium hydroxide
Sulfuric acid
glucose
C6H12O6 
Barium hydroxide
Sodium chloride
Ammonia(a weak base)
NH3 (aq) + H2O (l)
#5 Electrolytes and Nonelectrolytes
NH4+1(aq) + OH-1 (aq)
Rev F09AEM Fall 2009
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1.
In the fume hood**, there are two beakers with solid salts in them. Beaker A contains solid
sodium chloride. Beaker B contains solid calcium phosphate. Using these solids, and the
accompanying light-bulb set-ups, perform a conductivity test on them.
a.
Is the solid sodium chloride a good conductor?
b. Is the solid calcium phosphate a good conductor?
Yes
No
Yes
No
Using your answers above, explain why an ionic solid is (or is not) a good conductor of electricity:
_________________________________________________________________________________
_________________________________________________________________________________
2.
Return to your bench area. Obtain two 100-mL beakers and fill each with ~ 50 mL of distilled
water. Weigh out 0.5 grams of each solid. Into one beaker place the 0.5 grams of sodium
chloride. Into the other beaker, place the 0.5 grams of calcium phosphate. Record your
observations of each solid in the water. Now, test each solution with your conductivity set-up.
a.
Is the sodium chloride in water a good conductor?
b. Is the calcium phosphate in water a good conductor?
Yes
No
Yes
No
Briefly explain what is happening in solution for both solids that allows them to conduct or not
conduct electricity:
_________________________________________________________________________________
_________________________________________________________________________________
**
note: the location of the solid salts might have to change depending on space limitations. Ask the lab instructor if you cannot find
them in the hood.
Reflection questions:
1. Why must an electrolyte be added to water if it is to conduct electricity?
#5 Electrolytes and Nonelectrolytes
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2. Name the following compounds. Classify the following compounds as containing polar
covalent, nonpolar covalent, or ionic bonds. Predict the conductivity in solution (strong, weak,
or nonelectrolyte)? See the flowchart on p. 2 of the lab for help!
Name
Type of bond
Conductivity
NaBr
______________________________
___________________ ___________________
LiOH
______________________________
___________________ ___________________
HBr (aq)
______________________________
___________________ ___________________
HF (aq)
______________________________
___________________ ___________________
N2
______________________________
___________________ ___________________
3. Name the following ionic compounds. Classify them as soluble or insoluble in water using your
solubility guidelines. What is the conductivity in solution (strong or non-electrolyte)?
Name
Soluble/Insoluble
Conductivity
NaBr
______________________________ ___________________ ___________________
Ba(OH)2
______________________________ ___________________ ___________________
Ca3(PO4)2 ______________________________ ___________________ ___________________
MgCl2
______________________________ ___________________ ___________________
4. Consider the following titration reaction: HCl (aq) + AgNO3 (aq) → AgCl (s) + HNO3 (aq). If all
the HCl and AgNO3 reacted such that in the beaker there was only AgCl(s) and HNO3, if you
placed the lighbulb set up in the beaker, would you see it light up?
Beaker will light up? (circle one)
Yes
If it lights up, will it be bright or dim? (circle one)
No
Bright
Dim
If it lights up, which species is causing the light bulb to turn on? (circle all that apply)
AgCl(s)
HNO3 (aq)
AgCl(s) AND HNO3 (aq)
5. Why is it important to unplug the conductivity tester while cleaning the electrodes?
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