Conductivity of Solutions
Publication information:
Abstract
A light bulb is lit when a conductivity probe is immersed in an ionic solution.
Video of the demo in action https://youtu.be/4WillWjxRWw
What it Shows
Testing different solutions shows varying levels of conductivity based how much a solid ionizes in water when dissolved, or for pure liquids, the degree of ionization. The conductivity of a solution or pure liquid depends on its chemical composition.
How it Works
Liquid solutions and pure liquids can be classified as one of three types in terms of conductivity.1) Strong electrolytes: These are soluble ionic compounds, strong acids, and strong bases, which dissociate completely into ions in aqueous solution. Molten ionic compounds also conduct strongly.
2) Weak electrolytes: These are insoluble ionic compounds, weak acids, and weak bases. These substances only partially dissociate in solution, or partially ionize in the case of molecular acids and bases, yielding a small number of ions relative to the solution's concentration.
3) Nonelectrolytes: These are molecular substances that do not ionize, or to a very small extent. A nonelectrolyte is generally defined as having a conductivity of 1 x 10-8 ohm-1 m-1 or less. More details on the conductivity of liquids and how it is defined are discussed in Shakhashiri (1989).
Students need to know the conductivity of a substance in solution based on the substance's chemical composition. This will allow them to determine how a substance will dissolve and react in solution and will aid in writing chemical equations.
The conductivity tester works as follows. When plugged in and placed into a conducting solution, negatively charged ions move toward the cathode, and positively charged ions are attracted to the anode. The alternating current causes movement of the ions between the electrodes, creating an electrical current. The more ions in solution, the more charges can flow, and the higher the conductivity.
Setting it Up
Safety: Wear gloves and safety glasses/goggles. Though the tester's electrodes are encased in tubing, make sure not to contact them to metal or hands. Barium is a heavy metal - collect the barium sulfate solution as hazardous waste and dispose of it properly.
Prepare about 150 mL of the following solutions, all 0.10 M in concentration, in labeled 250 mL beakers: tap water, distilled water, sodium chloride, sucrose, acetic acid, hydrochloric acid, sodium hydroxide, ethanol, and barium sulfate. (See video: http://youtu.be/4WillWjxRWw?hd=1)
The simple conductivity tester consists of metal electrodes encased in tubing, attached to a lightbulb. Place it on the bench, for the instructor to plug in. An 800 mL beaker with 400 mL of deionized water is provided as a rinse station for use between samples.
Place the tester into each solution in the order given and have students record the brightness of the lightbulb for each. Rinse the tester thoroughly between solutions in the large beaker of distilled water. When cleaning up, neutralize the HCl and NaOH by mixing them together. Barium sulfate should be collected as hazardous waste, but the rest of the solutions can be poured down the drain
Comments
A simpler version of this demonstration can be done with tap water, distilled water, and table salt. Test the tap water and distilled water, then show that the distilled water can be made conductive by adding salt to it.
Increasing the concentration of ions increases the conductivity of a solution up to a point. At high concentration, ions may associate to form ion pairs as the distance between ions becomes smaller and smaller, which then decreases the conductivity (Zhang, 2020).
References
Experimental and Modeling of Conductivity for Electrolyte Solution Systems. Weitao Zhang, Xia Chen, Yan Wang, Lianying Wu, and Yangdong Hu. ACS Omega 2020 5 (35), 22465-22474. DOI: 10.1021/acsomega.0c03013
Electrical Conductivity of Liquids, Shakhashiri, B. Z. Chemical Demonstations: A Handbook for Teachers of Chemistry, Vol. 3; The Univ. of Wisconsin Press, Madison, WI, 1989; pp.326-328.
Full text
A light bulb is lit when a conductivity probe is immersed in an ionic solution.
Video of the demo in action https://youtu.be/4WillWjxRWw
What it Shows
Testing different solutions shows varying levels of conductivity based how much a solid ionizes in water when dissolved, or for pure liquids, the degree of ionization. The conductivity of a solution or pure liquid depends on its chemical composition.
How it Works
Liquid solutions and pure liquids can be classified as one of three types in terms of conductivity.1) Strong electrolytes: These are soluble ionic compounds, strong acids, and strong bases, which dissociate completely into ions in aqueous solution. Molten ionic compounds also conduct strongly.
2) Weak electrolytes: These are insoluble ionic compounds, weak acids, and weak bases. These substances only partially dissociate in solution, or partially ionize in the case of molecular acids and bases, yielding a small number of ions relative to the solution's concentration.
3) Nonelectrolytes: These are molecular substances that do not ionize, or to a very small extent. A nonelectrolyte is generally defined as having a conductivity of 1 x 10-8 ohm-1 m-1 or less. More details on the conductivity of liquids and how it is defined are discussed in Shakhashiri (1989).
Students need to know the conductivity of a substance in solution based on the substance's chemical composition. This will allow them to determine how a substance will dissolve and react in solution and will aid in writing chemical equations.
The conductivity tester works as follows. When plugged in and placed into a conducting solution, negatively charged ions move toward the cathode, and positively charged ions are attracted to the anode. The alternating current causes movement of the ions between the electrodes, creating an electrical current. The more ions in solution, the more charges can flow, and the higher the conductivity.
Setting it Up
Safety: Wear gloves and safety glasses/goggles. Though the tester's electrodes are encased in tubing, make sure not to contact them to metal or hands. Barium is a heavy metal - collect the barium sulfate solution as hazardous waste and dispose of it properly.
Prepare about 150 mL of the following solutions, all 0.10 M in concentration, in labeled 250 mL beakers: tap water, distilled water, sodium chloride, sucrose, acetic acid, hydrochloric acid, sodium hydroxide, ethanol, and barium sulfate. (See video: http://youtu.be/4WillWjxRWw?hd=1)
The simple conductivity tester consists of metal electrodes encased in tubing, attached to a lightbulb. Place it on the bench, for the instructor to plug in. An 800 mL beaker with 400 mL of deionized water is provided as a rinse station for use between samples.
Place the tester into each solution in the order given and have students record the brightness of the lightbulb for each. Rinse the tester thoroughly between solutions in the large beaker of distilled water. When cleaning up, neutralize the HCl and NaOH by mixing them together. Barium sulfate should be collected as hazardous waste, but the rest of the solutions can be poured down the drain
Comments
A simpler version of this demonstration can be done with tap water, distilled water, and table salt. Test the tap water and distilled water, then show that the distilled water can be made conductive by adding salt to it.
Increasing the concentration of ions increases the conductivity of a solution up to a point. At high concentration, ions may associate to form ion pairs as the distance between ions becomes smaller and smaller, which then decreases the conductivity (Zhang, 2020).
References
Experimental and Modeling of Conductivity for Electrolyte Solution Systems. Weitao Zhang, Xia Chen, Yan Wang, Lianying Wu, and Yangdong Hu. ACS Omega 2020 5 (35), 22465-22474. DOI: 10.1021/acsomega.0c03013
Electrical Conductivity of Liquids, Shakhashiri, B. Z. Chemical Demonstations: A Handbook for Teachers of Chemistry, Vol. 3; The Univ. of Wisconsin Press, Madison, WI, 1989; pp.326-328.