Experiment_622_Electrical Conductivity_1_1_3
- Page ID
- 305603
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Student Name |
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Laboratory Date: Date Report Submitted: |
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Student ID |
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Experiment Number and Title |
Experiment 622: Electrical Conductivity of Aqueous Solutions
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Experiment 622: Electrical Conductivity of Aqueous Solutions
Section 1: Purpose and Summary
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Observe the electrical conductivity of different substances in aqueous solutions.
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Determine whether the solution is a strong electrolyte, weak electrolyte, or nonelectrolyte.
The ability of a substance to conduct electric current is due to the movement or migration of ions in solution. Substances that are completely ionized in solutions are highly conducting and thus called strong electrolytes. Examples include salts, strong acids, and strong bases. Partially ionized substances, on the other hand, are weakly conducting and thus called weak electrolytes. Substances that do not ionize in solution are nonelectrolytes.
In this experiment, students will determine the conductivity of different aqueous solutions using a conductivity tester. Based on the results, students will classify each solution as strong electrolyte, weak electrolyte, or nonelectrolyte.
Section 2: Safety Precautions and Waste Disposal
Safety Precautions:
Use of eye protection is recommended for all experimental procedures.
Be careful when handling acid solutions. Even at low concentrations, acids may irritate your skin.
When using the conductivity tester, do not immerse the circuit board to water. Only the copper electrodes (metal probes) should be immersed and rinsed with laboratory water.
Waste Disposal:
While you are doing the experiment, collect your used aqueous solutions into a waste beaker.
When you are finished with the experiment, pour the contents of the waste beaker into the inorganic waste container in the fume hood.
Section 3: Procedure
Conductivity Testing – Evidence for Ions in Aqueous Solutions
Simple conductivity testers have a 9V battery and two parallel copper electrodes. Different styles of conductivity meters exist. The following is for a conductivity meter with a green and a red light-emitting diode (LED). Refer to the operating instructions on the specific use of your conductivity meter and adapt this procedure appropriately.
Use a wash bottle containing laboratory water and a ‘waste’ beaker to rinse the copper electrodes. Dry the copper electrodes completely with Kimwipes™ tissue.
When switched on, and the copper electrodes are dipped into a conducting solution, the LEDs will glow.
The photo shows the conductivity meter in a small beaker. Note that the electrodes are just submerged below the level of the liquid. The rest of the circuit board and battery power supply are kept dry.
It is very important to avoid contaminating solutions when moving the electrodes from one to another solution. It is a good idea to keep a separate container with laboratory water to use as a rinse solution between testing solutions. If you do this, change the laboratory water frequently.
The following key can be used to compare the conductivity of the solutions. This key is from the model which has a red and green LED. Other keys may need to be developed for other meters.
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Scale |
Red LED |
Green LED |
Conductivity |
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0 |
Off |
Off |
None |
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1 |
Dim |
Off |
Low |
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2 |
Medium |
Off |
Medium |
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3 |
Bright |
Dim |
High |
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4 |
Very bright/Blinking |
Medium |
Very high |
When testing samples/solutions, switch the conductivity tester on and dip the copper electrodes into the sample/solution.
After each test, switch the tester off, rinse the electrodes thoroughly with laboratory water, and dry with Kimwipes™. In addition, dispose the sample/solution and rinse the beaker thoroughly between tests.
Record your results on the table following this procedure.
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Sample/Solution |
Observations |
Conductivity |
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Red LED |
Green LED |
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Examples: LiOH(aq)
HNO2(aq)
Methanol, CH3OH(l) |
Bright
Dim
Off |
Dim
Off
Off |
High
Low
None |
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Sample/Solution |
Observations |
Conductivity |
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Red LED |
Green LED |
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Laboratory water |
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Tap water |
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NaCl(s) |
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NaCl(aq) |
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CaCO3(s) |
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CaCO3(aq) |
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0.1 M Acetic acid, HC2H3O2(aq) |
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“Glacial” Acetic acid, HC2H3O2 |
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0.1 M Al(NO3)3(aq) |
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15 M NH3(aq) |
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0.1 M Ca(OH)2(aq) |
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Ethanol, C2H5OH(l) |
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0.1 M HCl(aq) |
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Mg(OH)2 (sat. aq) |
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0.1 M MgSO4(aq) |
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0.1 M HNO3(aq) |
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0.1 M KI(aq) |
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0.1 M NaOH(aq) |
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Sparkling water |
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Sucrose, C12H22O11(aq) |
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Section 4: Data Analysis
Based on your observations, classify each sample as strong electrolyte, weak electrolyte, or nonelectrolyte. List them in the table below
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Strong electrolytes |
Weak electrolytes |
Nonelectrolytes |
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Post Lab Questions:
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Why must the copper electrodes in the conductivity tester, as well as the beaker, be rinsed with laboratory water after each test?
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Was there a difference in conductivity between laboratory water and tap water? Why do you think this is so?
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Was there a difference in conductivity between solid NaCl and aqueous NaCl? Why do you think this is so?
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Based on your results, among the tested substances, which are the:
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Strong acids
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Weak acids
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Strong bases
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Weak bases
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Write the chemical equations for the complete dissociation of at least three strong electrolytes listed in your data table in Section 4.