How to Calculate the pH of a Buffer Solution After Adding HCl?

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Discussion Overview

The discussion focuses on calculating the pH of a buffer solution after the addition of hydrochloric acid (HCl). The context involves applying concepts from acid-base chemistry, particularly in relation to buffer systems and equilibrium calculations.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant asks for guidance on calculating the pH of a buffer solution after adding HCl, specifying the concentrations of acetic acid and its conjugate base.
  • Another participant suggests using the acid dissociation constant (K_a) for acetic acid, noting it is approximately 1.8x10^-5, and emphasizes the need to set up an equilibrium table for the H^+ concentration.
  • A third participant mentions that HCl will react with the conjugate base, resulting in the consumption of the base and the production of more conjugate acid, and advises finding the new concentrations to solve for hydronium ion concentration.
  • A fourth participant provides a link to an external resource for pH calculations related to buffer solutions, suggesting that all added HCl is consumed in the reaction with the conjugate base.

Areas of Agreement / Disagreement

Participants generally agree on the approach to use equilibrium concepts and the reaction between HCl and the conjugate base. However, there is no consensus on the specific calculations or the final pH value, as the discussion remains exploratory.

Contextual Notes

Participants have not explicitly stated all assumptions, such as the complete dissociation of HCl or the specific conditions under which the buffer operates. The discussion does not resolve the mathematical steps involved in the calculations.

Who May Find This Useful

This discussion may be useful for students or individuals studying buffer solutions, acid-base chemistry, or those seeking assistance with similar homework problems.

nobb
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Hi.
I was wondering if someone could please explain how to do this question. Find the pH of 1 L buffer (1 mol/L CH3COOH, 1 mol/L CH3COO-) when 0.1 mL 1 mol/L HCl is added. Help would be appreciated. Thanks in advance.
 
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You are dealing with a weak acid, so you have to use the methods to solve for the H^+ concentration at equilibrium. I think the missing value from the question statement is that you need to use the K_a for acetic acid (which, if my memory doesn't decieve me, is something like 1.8x10^-5).

The HCl essentially disassociates completely; so when you are setting up your equilibrium table, you can treat the intial concentration of HCl as the initial conentration of "H^+" ions. When you are done, you can plug in your new values of CHOO- and CH3COOH into the relationship below and solve for the H^+ concentration (which you can then convert to pH):

1.8x10^-5 = [H^+][CHOO^-]/[CH3COOH]

Hope this all seems familiar to you ^^
 
that is the HCl will react with the conjugate base, which is consumed, and in turn produces more conjugate acid. Find the new concentrations, plug in, and solve for the hydronium ion concentration.
 

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