Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Bruhmoment on June 23, 2021, 02:25:20 AM
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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?
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I understand buffer capacity is higher when the ration of the reactants is close to 1:1?
What are these "reactants" you mentioned?
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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?
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It is never a bad idea to write a chemical equation.
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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?
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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.
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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?
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Cl- is NOT the conjugate base of NH4+.
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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
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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+?
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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.
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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.
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"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?
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"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?
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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.
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I don't see any errors. I usually write my table in terms of moles and only convert to molarity afterward, but other people may do it differently.
Oh my god this wasn’t even that bad in hindsight I’m not sure what was going on here. I’m gonna chalk it up to some fatigue maybe. Glad I finally got it correct. Thank you for the help, I’ve been struggling with some of the newer material.