Salt Solution Conductivity
Measuring the ability of a salt solution (sodium chloride, NaCl) to conduct electrical current.
Conductivity Sensor (PS-2116)
Lab Summary
Students will measure the ability of a salt solution (sodium chloride, NaCl) to conduct electrical current. As students increase the amount of salt added to the solution, they will predict how the solution’s conductivity will change.
Conductivity is a measure of the ability of a substance to conduct an electrical current. In liquids, the presence of free ions (positive and negative charges) is necessary for conductivity. When two electrodes, one positively charged and the other negatively charged, are introduced into a liquid containing free ions, the positive and negative ions will move in opposite directions (toward oppositely charged electrodes). This movement of charged particles constitutes an electric current through the liquid.
Solutions may or may not conduct electricity. Solutions that do not conduct electricity are called non-electrolyte solutions. Non-electrolytes are solutes that dissolve as molecules and therefore do not have any ions in solution. Since there are no charged particles in the solution, the solution does not conduct electricity. Solutions that conduct electricity are called electrolyte solutions. Electrolytes are solutes that dissociate into ions in solution. Electrolytes can be classified as strong or weak electrolytes depending on the degree to which their molecules dissociate in solution.
Strong electrolytes are better conductors of electricity because they dissociate completely (nearly 100%) into ions. Hydrochloric acid and nitric acid are examples of strong electrolytes. Weak electrolytes, on the other hand, are poor conductors because they dissociate to a very small extent in solution. Acetic acid and phosphoric acid are examples of weak electrolytes. In addition to the strength of an electrolyte, the degree to which an electrolyte solution conducts electricity also depends on the concentration of the electrolyte, the ions mobility in the solution, and the temperature of the solution.
For aqueous solutions, the most commonly used units of measurement for conductivity are microsiemens/centimeter (µS/cm) and millisiemens/centimeter (mS/cm). See "Teacher’s Hints" for more information about these standard units.
Published: February 2002
Downloads
- Salt Solution Conductivity - PASPORT (34 KB, .zip)
Includes experiment setup, procedures and Datastudio file
- Salt Solution Conductivity - ScienceWorkshop (34 KB, .zip)
Includes experiment setup, procedures and Datastudio file
Here's What You Need
U.S. Educator prices shown.
Probeware (PASPORT Systems)
Xplorer GLX (PS-2002) - $349
The Xplorer GLX is a data collection, graphing, and analysis tool designed for science students and educators.
PASPORT Conductivity Sensor (PS-2116A) - $110
Utilizes platinum probes for greater range and improved accuracy in high & low concentrations.
Probeware (ScienceWorkshop Systems)
750 Interface, USB (CI-7650) - $679
The 750 Interface allows students to measure force, temperature, pressure, angular velocity, acceleration, current, and magnetic field with a built-in function generator and oscilloscope mode.
10x Conductivity Sensor (CI-6739A) - $145
Used to explore the effect of temperature and concentration on the electrical transport properties of aqueous solutions.
Other Materials
- Distilled or deionized water
- Table Salt (0.5 gram)
- Balance to measure 0.1 gram of salt
- One 500-mL beaker, and a stirring rod
