[Bruhmoment]

For context I’ve got this problem here as part of a worksheet


“ consider a buffer solution prepared by adding .100 M HCl to 183 mL of .200 M ammonia. at what volume in mL of hydrochloride acid added will the buffer subsequently achieve its highest buffer capacity”


I’m completely lost as to how to solve this. I understand buffer capacity is higher when the ration of the reactants is close to 1:1? But how would this apply here?

[Borek]

I understand buffer capacity is higher when the ration of the reactants is close to 1:1?

What are these "reactants" you mentioned?

[Bruhmoment]

I understand buffer capacity is higher when the ration of the reactants is close to 1:1?

Alright so I was wrong, turns out it’s when the weak acid and it’s salt are in proportion that the buffer is at its highest. However, there is only HCl, a strong acid here.

What are these "reactants" you mentioned?

[Babcock_Hall]

It is never a bad idea to write a chemical equation.

[Borek]

it’s when the weak acid and it’s salt are in proportion that the buffer is at its highest.

This is a common misconception: buffer is not something consisting of an acid and its salt. Buffer is a mixture of an acid and its conjugate base, no matter where they come from.

Can you try to apply it here?

[Bruhmoment]

it’s when the weak acid and it’s salt are in proportion that the buffer is at its highest.

This is a common misconception: buffer is not something consisting of an acid and its salt. Buffer is a mixture of an acid and its conjugate base, no matter where they come from.

Can you try to apply it here?

So if I were to add NH3 to HCl, the resulting products would be Nh4 and Cl-

NH3 + HCl = NH4 + Cl-

So NH4 is going to be the weak acid, and NH3 is going to be the salt/conjugate base?

So adding HCl would increase the amount of NH4+ and Cl- 

Am I simply trying to find the volume at which the .0366 Mol of NH3 is 1:1 with the HCl? That would give an ander answer of 366 Ml of HCl, but I have no idea if that’s how to solve it.

[Bruhmoment]

it’s when the weak acid and it’s salt are in proportion that the buffer is at its highest.

This is a common misconception: buffer is not something consisting of an acid and its salt. Buffer is a mixture of an acid and its conjugate base, no matter where they come from.

Can you try to apply it here?

Wait hold on a minute


Is possible that all I have to do is

M1 V1 = M2 V2

So therefore my answer is 366 Ml?

[Borek]

Cl^- is NOT the conjugate base of NH₄⁺.

[Bruhmoment]

Cl^- is NOT the conjugate base of NH₄⁺.

Yeah I’m sorry but I’ve been at this problem all day trying to study for an and I’m unable to start it. I would appreciate a walkthrough but the furthest I’ve gotten is realizing that NH3 is the conjugate base of NH4+. I’m not sure how to find how much HCl I need for buffer capacity from there

[Bruhmoment]

Cl^- is NOT the conjugate base of NH₄⁺.

Yeah I’m sorry but I’ve been at this problem all day trying to study for an and I’m unable to start it. I would appreciate a walkthrough but the furthest I’ve gotten is realizing that NH3 is the conjugate base of NH4+. I’m not sure how to find how much HCl I need for buffer capacity from there

I know buffer capacity is at its highest when the weak acid and conjugate base are thus at nearly a 1:1 ration in concentration.

So adding HCl would end up treating more conjugate acid. So am I trying to find how much HCL would creat 0.0366 mole of NH4+?

[Babcock_Hall]

So if I were to add NH3 to HCl, the resulting products would be Nh4 and Cl-

NH3 + HCl = NH4 + Cl-

So NH4 is going to be the weak acid, and NH3 is going to be the salt/conjugate base?

So adding HCl would increase the amount of NH4+ and Cl- 

Am I simply trying to find the volume at which the .0366 Mol of NH3 is 1:1 with the HCl? That would give an ander answer of 366 Ml of HCl, but I have no idea if that’s how to solve it.

This is really more Borek's area than mine, but maybe writing an ICE table would help.  Minor point:  I would not call NH₃ a salt; it is the conjugate base of the ammonium ion.

[Bruhmoment]

So if I were to add NH3 to HCl, the resulting products would be Nh4 and Cl-

NH3 + HCl = NH4 + Cl-

So NH4 is going to be the weak acid, and NH3 is going to be the salt/conjugate base?

So adding HCl would increase the amount of NH4+ and Cl- 

Am I simply trying to find the volume at which the .0366 Mol of NH3 is 1:1 with the HCl? That would give an ander answer of 366 Ml of HCl, but I have no idea if that’s how to solve it.

This is really more Borek's area than mine, but maybe writing an ICE table would help.  Minor point:  I would not call NH₃ a salt; it is the conjugate base of the ammonium ion.

I see. For some reason my Professor calls it a salt so I’ve just been going with that.

. I’ve tried a few ice charts but at this point I’m starting to think either my answer key is wrong or I’m just not grasping something.

I’m starting charts with either NH3 + HCl or NH3 + H20 but I’m just not getting the right answer no matter what I do. I’ve been trying to solve this problem since about 8 am now so I’ve pretty much just given up.

[Babcock_Hall]

"I know buffer capacity is at its highest when the weak acid and conjugate base are thus at nearly a 1:1 ration in concentration."  This is correct.  If you added 366 mL of 0.1 M HCl, how much NH₃ remains at this point?

[Bruhmoment]

"I know buffer capacity is at its highest when the weak acid and conjugate base are thus at nearly a 1:1 ration in concentration."  This is correct.  If you added 366 mL of 0.1 M HCl, how much NH₃ remains at this point?

Okay so from my understanding

We make an ice table


NH3 + HCl = NH3 + Cl-

This is jn equilibrium and we are putting Everything in concentrations, so molarity.

We have an initiation 0.2 Molarity NH3 and a 0.1 Molarity HCL

The HCl is used up entirely giving us 0.1 NH3 left over, and creating 0.1 M NH4+ and 0.1 M Cl-

This means that the NH3 and the NH4+ are in equal concentration, so buffer capacity is reached.


This means that with 0.1 M at 183 mL, we have 0.0183 Mol of NH3.

So we would need 0.0183 Mol of HCl, and at 0.1 M that is 183 ml.

Is that it?

[Babcock_Hall]

I don't see any errors.  I usually write my table in terms of moles or millimoles and only convert to molarity afterward, but other people may do it differently.