Tbr cbt 7 #16

[kehlsh]

Ok let me rephrase the q.

For the titration of H2SO4 with Ba(OH)2.

why would equivalence point be 7 if H2SO4 dissociates to HSO4(-1), which is a weak acid?
If equivalence is at 7, why would the precipitate be BaSO4 (obvious, I know) and not Ba(HSO4)2 since HSO4(-1) is a weak acid and would hardly dissociate?

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[justhanging]

Ok let me rephrase the q.

For the titration of H2SO4 with Ba(OH)2.

why would equivalence point be 7 if H2SO4 dissociates to HSO4(-1), which is a weak acid?
If equivalence is at 7, why would the precipitate be BaSO4 (obvious, I know) and not Ba(HSO4)2 since HSO4(-1) is a weak acid and would hardly dissociate?

Your mixing a strong acid and strong base so it will be 7. Since your adding a base your going to abstract all the protons from the acid so even though HSO4 barely dissociates, with a base present it is going to dissociate completely. Another way you can think about it is that SO4-2 is a weaker base then Ba(OH)2

 

[kehlsh]

Your mixing a strong acid and strong base so it will be 7. Since your adding a base your going to abstract all the protons from the acid so even though HSO4 barely dissociates, with a base present it is going to dissociate completely. Another way you can think about it is that SO4-2 is a weaker base then Ba(OH)2

I don't think you are getting what I'm asking, thanks though.

I know that strong/strong is equivalence of 7 pH. But H2SO4 is kinda different because HSO4- is a weak acid... so shouldn't equivalence point go up to more than a 7? (just like how weak acid/strong base you get equivalence of greater than 7)

 

[justhanging]

I don't think you are getting what I'm asking, thanks though.

I know that strong/strong is equivalence of 7 pH. But H2SO4 is kinda different because HSO4- is a weak acid... so shouldn't equivalence point go up to more than a 7? (just like how weak acid/strong base you get equivalence of greater than 7)

I see what your saying. It sort of like titrating a strong base, strong acid then when all the H2SO4 is gone and only HSO4 remains it is titrating a strong base, weak acid. The only reason I could find as to why it is not higher then 7 is because BaSO4 is not soluble in water so the reaction of SO4 + H2O --> HSO4 + OH doesn't happen because there are no SO4 in solution. Maybe there is a better reason idk...

 

[Der Kaiser]

Is it because Ba(OH)2 also has two base dissociation constants (two hydroxide ions to dissociate)?

 

[kehlsh]

Is it because Ba(OH)2 also has two base dissociation constants (two hydroxide ions to dissociate)?

I don't think so they just completely dissociate I think. GAH....😕😕😕

 

[PingPongPro]

Post the question to make it more clear. I think there might be some parts that were ommitted.

The pH=7 at equivalence point because it is a titration between a strong acid and strong base. I think you know that, but when you say e.p=7, you actually mean FIRST equivalence point is 7. So when titrating diprotic acid with strong base, all of the strongly acidic proton will be deprotonated before any of the 2nd one is. That is why we are at pH=7 at the first equivalence point. [Strong base] = [Strong acid].

You are probably wondering about how BaSO4 forms now. Well it is kind of confusing, but it is simply due to molar ratios. Ba(HSO4)2 may make sense since it has no net charge, but the molar ratios don't allow it. For each Ba(OH)2 molecule, 2 protons will be dissociated per Ba. So Ba(HSO4)2 cannot form because if Ba had already lost the 2 OH-, then the proton from HSO4 would have already been deprotonated.

You said HSO4- is a weak acid and doesn't dissociate, so why would the precipitate form? Well you are kind of applying acid definitions incorrectly here. HSO4 is a weak acid, and its true, it wouldn't dissociate in water. However, this question has a strong base to fully deprotonate the weak acid, so perciptate can form.


I think there is confusion because you are essentially asking 2 different questions. One is about acid/base salt reaction, and the other is about titrations at first equiv. point.

 

[kehlsh]

Post the question to make it more clear. I think there might be some parts that were ommitted.

The pH=7 at equivalence point because it is a titration between a strong acid and strong base. I think you know that, but when you say e.p=7, you actually mean FIRST equivalence point is 7. So when titrating diprotic acid with strong base, all of the strongly acidic proton will be deprotonated before any of the 2nd one is. That is why we are at pH=7 at the first equivalence point. [Strong base] = [Strong acid].

You are probably wondering about how BaSO4 forms now. Well it is kind of confusing, but it is simply due to molar ratios. Ba(HSO4)2 may make sense since it has no net charge, but the molar ratios don't allow it. For each Ba(OH)2 molecule, 2 protons will be dissociated per Ba. So Ba(HSO4)2 cannot form because if Ba had already lost the 2 OH-, then the proton from HSO4 would have already been deprotonated.

You said HSO4- is a weak acid and doesn't dissociate, so why would the precipitate form? Well you are kind of applying acid definitions incorrectly here. HSO4 is a weak acid, and its true, it wouldn't dissociate in water. However, this question has a strong base to fully deprotonate the weak acid, so perciptate can form.


I think there is confusion because you are essentially asking 2 different questions. One is about acid/base salt reaction, and the other is about titrations at first equiv. point.

Are you saying precipitate would form after the equivalence point?
Are you saying at equivalence point [HSO4-] = what?
The equivalence point would be where [SO4(2-)] = [Ba(2+)], and it will be at pH of 7, that's where my confusion lies at the core.

 

[PingPongPro]

Do you know the difference between first equivalence point and second equivalence point?

 

[kehlsh]

Do you know the difference between first equivalence point and second equivalence point?

I know that. I'm not an idiot.

I guess this helps me to understand the most:

http://www.titrations.info/acid-base-titration-sulfuric-acid

 

[BerkReviewTeach]

Ok let me rephrase the q.
For the titration of H2SO4 with Ba(OH)2. why would equivalence point be 7 if H2SO4 dissociates to HSO4(-1), which is a weak acid?
If equivalence is at 7, why would the precipitate be BaSO4 (obvious, I know) and not Ba(HSO4)2 since HSO4(-1) is a weak acid and would hardly dissociate?

Is knowing the pH at the second equivalence point necessary to answer the question? It's an interesting question you pose, but it's a curiosity that is unnecessary on question #16. The question asks for the identity of the precipitate when the current through the solution is 0 amps. The only way to get a current of 0 is to have no ions in solution to allow it to conduct. This means that Ba(OH)2 and H2SO4 must have completely reacted to form water an a precipitate of some sort. Because the precipitate is a crystallized salt, it must be neutral, so the only two choices that are physically possible are BaSO4 and Ba(HSO4)2. This question has more to do with solubility at this point than acid-base or electrical flow. Ba(HSO4)2 is going to be more soluble than BaSO4 because (+2) w/ (-2) is a stronger attraction than (+2) w/ (-1). That is supported in part because a salt of Ba(HSO4)2 would likely dissociate to generate a weakly acidic solution, and that would in turn allow the current to conduct. Only by adding more OH- would you be able to get rid of the hydronium ion in solution, which would increase the number of Ba2+ in solution until all of the hydronium from sulfuric acid was consumed. At that point, the moles Ba2+= moles SO42-, so the salt would completely crash out of solution based on the magnitude of Ksp.

To answer your question about the pH, I'm going to piggyback on a few previous posts. What is unique here is the impact of solubility on the equilibrium. Because Ba2+ completely precipitates with the SO42-, there is no equilibrium in solution involving HSO4- to worry about, so there are no ions in solution (hydronium, hydroxide, or other). Think about it this way. If you took a piece of granite and added it to distilled water, would the pH go up or down? The fact is that the rock wouldn't do anything (it's insoluble) and the pH would remain at 7. BaSO4 is a rock in distilled water when the current is 0.