TBR: Base Electrical Conductivity

[MelloTangelo]

Chemistry, Book 1: p. 270, question 8.

8. How can it be explained that there is no difference between the current readings of .1M KOH, and .1M KOAc.

A. Both of them are strong bases
B. Both of them are weak bases
C. Neither compound dissociates into ions in water
D. The number of ions in solution does not depend on base strength

Answer: D

Maybe I'm over-complicating a very simple problem--actually, I'm sure I am, but I just wanted some clarification. Because they are both made up of one cation and one anion, they dissociate completely and the number of ions in the solution are the same, according to the answer.

I guess what's confusing me a little is why the base strength does not affect this effect. I would think KOH would dissociate a lot more, being a strong base, and thus would have a greater concentration of product, making it more conductive. Do they both completely dissociate just because they're salts?

Also, I guess that electricity would conduct regardless of whether it was an acid or a base that dissociated? All it needs are ions in the solution?

Thanks for the help in advance, folks.

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[The Brown Knight]

Yes, they will dissociate completely because they are potassium salts.
Think of it like this:
1) 0.1M KOH: when you add the KOH to water, you will have K+ and OH-; now the OH- can abstract a proton from a water molecule but that will just create a water molecule and another OH- --> hence you have 0.1 M of each ion.
2) 0.1M KOAc: when you add the KOAc to water, you will have K+ and OAc-; now the OAc- can abstract a proton from water to form HOAc and OH-
point is, you still have 0.1M of each ion in this case as well.
Hence, the similar electrical properties. And yes, conduction needs ions - any ions.

 

[justadream]

@The Brown Knight

If you had used a base that did not dissociate differently, would the answer be different?

 

[The Brown Knight]

@The Brown Knight

If you had used a base that did not dissociate differently, would the answer be different?

Can you give an example?
As long as it's ionic, any base will provide the same conductivity, even if it's as weak as iodide.

 

[justadream]

@The Brown Knight

Idk any base with a super low Kb?

Because that would mean the base doesn't dissociate very much into ions.

 

[The Brown Knight]

@The Brown Knight

Idk any base with a super low Kb?

Because that would mean the base doesn't dissociate very much into ions.

You, obviously, can't use something like ammonia since it can't form an ionic solid with K+
But something like I- or Br- would have a very low Kb, but either will still have same conductivity as the ones OP mentioned (as long as they are same concentration)

 

[justadream]

@The Brown Knight

Okay so with K+, you'd form an ionic compound so no matter what, it will fully dissociate and have the same conductance as a strong base would.

But if I used a base that did not involve K+ and that was weak, then I could have a situation with LESS conductance?

 

[The Brown Knight]

@The Brown Knight

Okay so with K+, you'd form an ionic compound so no matter what, it will fully dissociate and have the same conductance as a strong base would.

But if I used a base that did not involve K+ and that was weak, then I could have a situation with LESS conductance?

Yeah, if you used 0.1 M NH3, you'll have some ions but lot fewer than the solutions mentioned by OP and hence lesser conductivity

 

[justadream]

@The Brown Knight

Okay gotcha. So anytime you have an ion, it completely dissociates. But you should not make conclusions about base strength based on dissociation (since KOAc is a weak base that fully dissociates).