[JoshP]

Hey guys,

Just doing a question about a conductometric titration involving adding a strong acid (HCl) to a weak base (aqurous ammonia). I have some thoughts on it but kind of wanted to check them/see if I was missing anything! Basically, I figured that at the start of the titration you've got a fairly decent conductivity due to the OH- in the NH3 (aq). As you add acid, these get replaced by chlorides, which with their lower ion mobility result in the conductivity decreasing. After neutralisation, you're adding excess HCl. At this point, I figured the conductivity would increase due to the addition of H+ (v. high ion mobility). However, I didn't know if I ought to consider any equilibrium changes due to adding more chloride to something already containing chloride (le chatalier etc). If so, is that going to affect the conductivity? Hope I made myself clear - I'd appreciate any answers!

Cheers, Josh

[Borek]

Ammonia is a weak base.

[JoshP]

Ammonia is a weak base.

Indeed it is - could you perhaps elaborate?

[Borek]

Is it 100% ionized in the solution? If you add acid - does the number of conducting ions grows, or goes down?

[JoshP]

Well that's kind of what I'm unsure about - at first I just thought it would go up, because you are adding more ions. But then, is adding more ions going to alter any equilibria, which would affect conductivity? Perhaps I'm not understanding what you're getting at, could you be a bit more blunt?!

Josh

[Borek]

You replace some ammonia (which was partially dissociated) with fully protonated NH₄⁺ and Cl^-.