Acid/Base Neutralization (BR)

[MDPhDJourney]

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According to berkely review:

"a weak base and a strong base of the same concentration require the same moles of acid to be neutralized...because the moles of hydroxide are the same for equimolar bases, regardless of their strengths"

Could someone explain to me why this is true? I assumed that a stronger base would require more moles of acid to be neutralized because it would yield more Hydroxide in solution that needs to be neutralized...what's wrong with my reasoning?



Possible Answer:
Is it because the acid will also react with the base molecules that have not dissociated into hydroxide?


Thanks!

 

[MedPR]

According to berkely review:

"a weak base and a strong base of the same concentration require the same moles of acid to be neutralized...because the moles of hydroxide are the same for equimolar bases, regardless of their strengths"

Could someone explain to me why this is true? I assumed that a stronger base would require more moles of acid to be neutralized because it would yield more Hydroxide in solution that needs to be neutralized...what's wrong with my reasoning?



Possible Answer:
Is it because the acid will also react with the base molecules that have not dissociated into hydroxide?


Thanks!

Neutralization just means acid + base reacting to form a salt. If the desired pH is 7, then you will need more weak acid/weak base than strong acid/strong base.

 

[MT Headed]

In terms of base 'strength', a stronger base will release more OH- into solution and keep less in reserve, while a weaker base will release less OH- into solution and keep more in reserve bound up to the molecule.

So if you put one mole of a strong base like NaOH into solution, it will dissociate 100% and you will have one mole of OH- floating around that needs to be neutralized.

But let's say you put one mole of NH3 into solution. Some of it will remain NH3 and some will react with water and become NH4+ ions and OH- ions. It's a weak base. There are fewer OH- ions floating around at any given time. Let's say only half a mole of OH is floating around.

Aha you think, I only need to add half a mole of acid to neutralize those OH ions and i'm done! But as soon as you remove those OH ions, the equilibrium will shift to create more OH ions. So you have to add more acid. And more. Until finally you've added a mole of acid and completely neutralized all of the weak base.

 

[indianjatt]

To add to MT Headed, I'd just like to point out that thinking in terms of le chatlier's principle always help. A weak base won't dissociate completely, low kb, but if you have an acid then the acid will neutralize all of the OH- it does produce. Now, "temporarily," lets assume we have no OH-, but we still have some weak base left. According to le chatlier's principle, the equilibrium will shift to the right in order to produce more OH- until all the acid neutralizes the weak base.

 

[MDPhDJourney]

In terms of base 'strength', a stronger base will release more OH- into solution and keep less in reserve, while a weaker base will release less OH- into solution and keep more in reserve bound up to the molecule.

So if you put one mole of a strong base like NaOH into solution, it will dissociate 100% and you will have one mole of OH- floating around that needs to be neutralized.

But let's say you put one mole of NH3 into solution. Some of it will remain NH3 and some will react with water and become NH4+ ions and OH- ions. It's a weak base. There are fewer OH- ions floating around at any given time. Let's say only half a mole of OH is floating around.

Aha you think, I only need to add half a mole of acid to neutralize those OH ions and i'm done! But as soon as you remove those OH ions, the equilibrium will shift to create more OH ions. So you have to add more acid. And more. Until finally you've added a mole of acid and completely neutralized all of the weak base.

MT Headed, your explanation was perfect!


Thanks!