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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: alexanda on January 31, 2015, 03:54:50 AM

Title: conductivity at end point
Post by: alexanda on January 31, 2015, 03:54:50 AM

Hi guys I know this may be a silly question, but I cant figure out why the conductivity of electricity is amlost zero at the end point of a titration...simply because there are no mobile ions?

Btw conductivity of electricity depends on mobile ions or free electrons right?

Gracia!

Title: Re: conductivity at end point
Post by: Borek on January 31, 2015, 06:05:13 AM

Conductivity in water depends solely on ions (hydrated electrons are pretty exotic).

Exact shape of the curve depends on the titration type. Sometimes it has a minimum at equivalence, but not zero.

Try to imagine what ions are present on what concentrations in the solution during titration. Remember, that conductivity of H⁺ and OH^- is much larger than conductivity of any other ion.

Title: Re: conductivity at end point
Post by: alexanda on February 01, 2015, 12:41:35 AM

Ok i get it
as there are almost the equal numbers of H+ and OH- ions at the end point, so the conductivity of the solution is the minimum
is that the explanation?

Title: Re: conductivity at end point
Post by: Borek on February 01, 2015, 03:51:31 AM

It is not about them being equal, it is about the total - sum of their concentrations (actually a weighted sum).

Think about the concentration of both of these ions at pH 5 and 9 (before and after the endpoint). How many times their concentrations are larger than at pH 7?