Conductivity of solutions

[helphelp]

Hi

 

Can you someone please explain why one particular electrolyte solution conducts electricity better than an another. Specifically NaCl and KI solutions? I understand the process of ionic conductivity but can't seem to get my head around why NaCl or KI will conduct electricity better??

 

Thanks for anyone's help, it is greatly appreciated!!

[Sensei]

NaCl dissolved in H2O is in reality ions Na+ and Cl-. They are spread evenly across of whole water, so we can say that distances between ions are pretty much equal (none part of water has higher concentration).

 

From quantum physics point of view Sodium is giving away its electron (because it wants to have 2,8 electrons in shells, instead of 2,8,1), and Chlorine is taking electron (because it wants to have 2,8,8 electrons, instead of 2,8,7).

Edited November 5, 2013 by Sensei

[Enthalpy]

Electrolyte conductivity depends on the charge count of the ions and their mobility. The mobility depends on anything, so it's eperimental. At low concentrations, the mobility depends little on the concentration.

 

Ions separate in a polar solvent because solvent molecules surround them to bring the adequate charge (from their ends) near the ions. Consequently, ions don't move alone in an electrolyte: they move with many solvent molecules together. That's why so simple relation exists between ion mobility or the mass or size of the ion - different number of solvent (water) molecules moving with the ion make it more or less heavy and bulky.

[lab14lab]

Hi,

 

I want to design a conductivity sensor consisting of coaxial cylindrical electrodes in order to measure the electrical conductivity of solutions. There is not much literature out there that describes this in great detail. Would you guys be able to recommend any textbooks or anything as to how I should go about the design and how these type of sensors work?

 

Many thanks

[Enthalpy]

The effect of metal-to-electrolyte contact tends to overshadow the electrolyte's behaviour, so you could think first at what metal to use, and under which electrical conditions - for instance, have different current densities with the same polarization and observe only the differences, than again with reversed polarity, and take a mean.

 

Knowing that the contacts introduce errors, I'd check if a "four-point method" can be used wth electrolytes. In solid semiconductors, this method injects current through two outer electrodes and measures a voltage at two inner electrodes. This avoid the mistake by the voltage drop at the injecting electrodes. A geometry computation relate the voltage, current and resistivity. Have four lines, or two plates and two picks, if it's better. Then again, consider AC.

[rktpro]

There are theoretical explanations for conductivities of ions. Foe ex, down the group though mass increases but conductivity decreases as the ions becomes less solvated and more mobile. I considered a polar solvent here. The high conductivity of OH- and H+ are explained differently.

There are theoretical explanations for conductivities of ions. Foe ex, down the group though mass increases but conductivity decreases as the ions becomes less solvated and more mobile. I considered a polar solvent here. The high conductivity of OH- and H+ are explained differently.

[rktpro]

Sorry, mistyped. Down a group conductivity increases