Finding the pH of this acid and its sodium salt solution

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Discussion Overview

The discussion revolves around finding the pH of a weak acid and its sodium salt solution, focusing on the application of equilibrium laws and the relevant equations necessary for such calculations. Participants explore the relationship between weak acids and bases, and the concept of buffers.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant describes using the equilibrium law to determine the degree of dissociation and [H+] concentration for the acid but expresses difficulty in finding the pH of the salt solution.
  • Another participant emphasizes the need to write down relevant equations, stating it is essential for solving the problem.
  • Some participants suggest that finding the pH of a weak acid is analogous to finding the pOH of a weak base, proposing that the same approach can be applied.
  • There is a question raised about whether the solution constitutes an acidic buffer.
  • One participant asserts that there is no buffer present and explains that the concentration of H+ can be calculated from the known initial concentration of the acid and its dissociation constant.
  • A later reply reiterates the importance of relevant equations and expresses frustration over recurring issues with standard calculations in this area, while also providing a pH value of 7.94.
  • Another participant critiques the use of significant figures in the provided pH value.

Areas of Agreement / Disagreement

Participants express differing views on whether the solution is an acidic buffer and the necessity of writing down relevant equations. The discussion remains unresolved regarding the specific approach to finding the pH of the salt solution.

Contextual Notes

Limitations include the lack of specific equations presented by the original poster, which may hinder the clarity of the discussion. There are also unresolved assumptions regarding the nature of the acid and salt involved.

Kaushik
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Homework Statement
The Ionization constant of chloroacetic acid is ##1.35 * 10^{-3}##. What will be the pH of 0.1M acid and its 0.1M sodium salt solution?
Relevant Equations
## K_w = K_a * K_b ##, ##K_b = \frac{[OH^-][CH2ClOOH]}{[CH2ClOO^-]}##
For finding the pH of the acid, I made use of the equilibrium law (or the law of mass action) to arrive at the degree of dissociation which I later used to get the [H+] concentration.

I am stuck in finding the pH of the salt solution.

##CH2ClOO^- + H2O <---> CHClOOH + OH^-##

Could you please help me out?
 
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The template asks you to write down the relevant equations. You have not done so, not even the ones you used to get your result so far. It is however however an essential step for this kind of problem.
 
Finding pH of a weak acid is not different from finding pOH of a weak base. If you know how to do the former, just follow the same approach to do the latter.
 
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Borek said:
Finding pH of a weak acid is not different from finding pOH of a weak base. If you know how to do the former, just follow the same approach to do the latter.
So is it an acidic buffer?
 
Kaushik said:
So is it an acidic buffer?
Your problem is about a salt.
 
No buffer here.

When you have solution of an acid, you can calculate concentration of H+ from the known initial concentration of the acid and its dissociation constant.

When you have solution of a base, you can do exactly the same, just instead of H+ you will be calculating concentration of OH-.
 
epenguin said:
The template asks you to write down the relevant equations. You have not done so, not even the ones you used to get your result so far. It is however however an essential step for this kind of problem.

Oh well, this is not the first or second time that for a problem in this area I asked for the relevant equations and that ended the thread. So I suppose as soon as you write them down you know what to do. (Ready to help but I do wonder sometimes when I see a question about some extremely standard calculation which is in all the books with worked examples!)

Anyway, for all these pH problems it is always the same, there are three equations (or for rare more complicated problems three types of equation) plus some simplifying assumptions or approximations which are essential to learn about, and also have a grasp of how good they are and their limits.

I got pH = 7.94
 
epenguin said:
Oh well, this is not the first or second time that for a problem in this area I asked for the relevant equations and that ended the thread. So I suppose as soon as you write them down you know what to do. (Ready to help but I do wonder sometimes when I see a question about some extremely standard calculation which is in all the books with worked examples!)

Anyway, for all these pH problems it is always the same, there are three equations (or for rare more complicated problems three types of equation) plus some simplifying assumptions or approximations which are essential to learn about, and also have a grasp of how good they are and their limits.

I got pH = 7.94
-10 pts for using the wrong # of significant figures!
 

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