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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: University_Of_Toronto on November 03, 2007, 12:55:16 AM

Title: Units for Buffer capacity
Post by: University_Of_Toronto on November 03, 2007, 12:55:16 AM

   
Buffer capacity (Acid/HCl) = -1/slope * [HCl]/ Vol_buffer

I ended up with mol/L...just wondering if it is correct

Title: Re: Units for Buffer capacity
Post by: Borek on November 03, 2007, 05:22:46 AM

TBH I have no idea what you wrote - what does "Acid/HCl" means? Is that you buffer definition capacity? If so, isn't HCl an acid? Doesn't it cancel? How can you calculate buffer capacity not taking pH change into account? Something is wrong.

http://www.chembuddy.com/?left=pH-calculation&right=pH-buffer-capacity

Title: Re: Units for Buffer capacity
Post by: University_Of_Toronto on November 03, 2007, 11:43:30 PM

Well you focus on the what (HCl/NaOH) means rather than focusing on the question...the question remained unanswered but I will explain to you what  buffer capacity(HCl/NaOH) means

If you add HCl/NaOH to a buffer then the

Experimental buffer capacity can be calculated from the slopes of the graphs of pH vs NaOH added or pH vs HCl added

Experimental Buffer capacity= 1/m_HCl * Con_HCl / V_buffer

Now you are refering to theoretical Buffer capacity which is

B(beta) =[(H + Kw/H + Ka CH/(Ka +H)²] ln (10)


I dont know but it seems there are too many police here rather than people who are willing to atleast provide some assistance

I already got what I wanted from the link you provided but thanx anyways

Title: Re: Units for Buffer capacity
Post by: Borek on November 04, 2007, 04:53:36 AM

Quote from: University_Of_Toronto on November 03, 2007, 11:43:30 PM

Well you focus on the what (HCl/NaOH) means rather than focusing on the question...the question remained unanswered but I will explain to you what  buffer capacity(HCl/NaOH) means

No, I am focusing on what you mean - it is impossible to answer the question without understanding it :) And your post was - at least for me - far from being clear.

Quote

Experimental buffer capacity can be calculated from the slopes of the graphs of pH vs NaOH added or pH vs HCl added

Experimental Buffer capacity= 1/m_HCl * Con_HCl / V_buffer

Assuming you started with mentioned plot, slope = ΔpH/ΔV, so buffer capacity is

Experimental Buffer capacity=  ΔV/ΔpH * Con_HCl / V_buffer

Now, when it comes to units volume cancels out and you are left with concentration/pH - if we assume pH is unitless, what is left is concentration - so you were OK from the begining. Not knowing what you mean by "slope" there was no way of checking.

Title: Re: Units for Buffer capacity
Post by: University_Of_Toronto on November 04, 2007, 11:16:54 AM

Thank you Borek..you deh man  ;D