USING CONDUCTIVITY TO PREDICT BONDING
AND THE PRESENCE OF ELECTROLYTES LABORATORY ACTIVITY
When ionic substances dissolve in water, the ions separate from each other. When some molecular substances dissolve
in water, they remain in molecular form; other molecular substances go through a process called ionization to a greater
or lesser degree. The generalized differences among these phenomena can be represented by these equations:
A+B¯ (s) → A+(aq) + B¯(aq)
AB(s) → AB(aq)
AB(s) → A+(aq) + B¯(aq)
PURPOSE:
Ionic compound separates into ions.
Molecular compound dissolves.
Molecular compound ionizes in solution.
In this activity you well determine the degree to which substances produce ions in aqueous solution or
simply test for the presence of ions. This in turn will allow you to make a prediction as to the type of
bonding that may be present; ionic or molecular.
Electrolytes are substances that produce ions in aqueous solutions. Nonelectrolytes do not form ions in solution.
When ions are present in a solution, the light bulb of a conductivity apparatus will glow because the ions complete an
electrical circuit. A nonelectrolyte produces only molecular substances which do not carry a current in an aqueous
solution. The light bulb in the conductivity apparatus does not glow. Weak electrolytes produce only a few ions: the
light bulb will glow weakly. We can identify substances in aqueous solutions as electrolytes, weak electrolytes or
nonelectrolytes on the basis of our observations of the conductivity apparatus.
PROCEDURE: *Note: the most difficult part of this lab is to try to not contaminate your solutions
1.
Make a data table that includes each of the compounds and solutions to be tested. Include columns to include
the following results:
• solid or solution
• type of conductor: strong electrolyte (conducted strongly), weak electrolyte (conducted weakly),
nonelectrolyte (no conduction)
• ions present (yes or no)
• type of compound/solution predicted based on observation (ionic or molecular)
• Equation representing your observation (Does it dissociate or not?)
2.
3.
4.
*Note: the most difficult part of this lab is to try to not contaminate your solutions
Cut a straw at an angle for use as a scoopula for each of the solid compounds to be tested to avoid
contamination. Use a few drops of water in a spot plate to dissolve the solids for each of the trials below. Use
the conductivity tester to determine the relative conductivities of the following:
a) tap water b) distilled water c) distilled water containing dissolved C12H22O11 d) distilled water containing
dissolved NaCl e) distilled water containing a tiny amount of dissolved (KNO3). f) distilled water containing a
greater amount of KNO3 g) a few drops of HC2H3O2(aq) h) a few drops of HCl(aq)
Utilizing the spotplate, test each compound with the conductivity detector:
a) If it is a solid compound, does the solid conduct?
b) Then, if it is a solid, add a few drops of distilled water to each well and stirring to put the solid compound into
solution and test the compound again as an aqueous solution. Does the solution conduct?
c) If it is a solution, add a few drops of the solution to a microplate or spot plate and test.
Test any other compounds or solutions that may be available as above. Be sure to include these on your data
table for easy reference in your discussion write up.
LAB QUESTIONS:
1.
How is the presence of ions related to conductivity?
2.
What generalization can you make about the number of ions produced by:
a) electrolytes, b) nonelectrolytes, c) weak electrolytes?
3.
Why does the tap water, but not the distilled water conduct electricity?
4.
Why does distilled water containing dissolved potassium nitrate conduct electricity? What are the charge carrying
particles?
5.
Why does distilled water containing dissolved sugar not conduct electricity?
6.
Compare the conductivity of HC2H3O2(aq) versus HCl(aq). Describe this observable difference and why it is so.
7.
Write an equation for the reaction of each of the compounds and solutions you tested based on your results.
WRITE UP: Follow the standard laboratory write up of Title, Purpose, Equipment, Labeled Equipment Diagram,
Reagents, Procedure, Data Table, Observations, Discussion, Lab Questions and Conclusion.