29 Jun, 2013
PRESENTATION: The conductivity of a dissolution relates to the existence of dissolved salts. Their dissociation generates cations and anions capable of transporting the electric energy under the action of a difference in the electric potential.
- The Salty Science of the Aluminum-Air Battery, Stephanie V. Chasteen, N. Dennis Chasteen, and Paul Doherty,Phys. Teach. 46, 544 (2008)
INTRODUCTION: Conductivity is the measure of the facility with which the electrolitical current flows through a solution, it varies according to:
- Temperature coefficient (α): depends on the nature and concentration of the electrolyte. It is found in the resistance formula depending on the temperature changes.
- Nature: it depends on the kind of material used.
- Concentration: if it rises, the conductivity increases because the number of ions that can carry electric current is higher. Up to the maximum level when it starts diminishing because the interactions among ions make conduction difficult.
OBJECTIVE: To observe the conductivity in water depending on the temperature and on the concentration of the dissolution.
MATERIALS: electric bulb, cables, salt, water, container, battery, electrodes (nickel-plated clips).
SETUP: A series circuit is set up formed by battery, electrodes, electric bulb and cables. The electrodes are introduced in a contained with water. As the salt is poured and/or the temperature is raised the bulb will give light with higher intensity.
EXPLANATION: When we introduce the electrodes in water with null concentration, we observe that there is no electricity flow- As we add salt the electrical charges are transported by the ions Na-Cl. The difference in potential between them makes the ions move. The positives are attracted by the cathode and the negative by the anode. Due to that, it is possible that there is an electric current in the liquid.
CONCEPTS: temperature coefficient, molar conductivity, electrolysis.
- R. Serway, Física, Mac Graw Hill, 2010.
- P. Tipler, Física para la Ciencia y la tecnología, Reverté, 2012.
- R. Ehrlich, Turning the World Inside Out and 174 Other Simple Physics Demonstrations, Princeton University Press, 1997.
STUDENTS 2012-2013: Jesús M. Gómez, Carolina Gil, Alba González
LINK pdf STUDENTS (in Spanish):