Solving pH of an Aqueous Solution of Weak Acid HCOOH

Click For Summary

Discussion Overview

The discussion revolves around calculating the pH of an aqueous solution of the weak acid formic acid (HCOOH) at a concentration of 0.689 mol/L. Participants are addressing the equilibrium expression and the dissociation constant (Ka) relevant to the problem.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks assistance in writing the equilibrium expression for the dissociation of formic acid in water, indicating uncertainty about the chemical reaction involved.
  • Another participant describes the reaction as a neutralization reaction, noting that water acts as a base and that its concentration is not included in the Ka expression.
  • A participant challenges the reported Ka value, stating it is one magnitude wrong and suggesting it should be 1.8 x 10^(-5), which is ten times smaller than the value initially provided.
  • Another participant asserts that the Ka value of 1.8 x 10^(-4) is indeed correct for formic acid and encourages checking the lecture material on weak acid pH calculations.
  • A later reply expresses understanding of the discussion, indicating some level of clarity achieved.

Areas of Agreement / Disagreement

There is disagreement regarding the correct value of the dissociation constant (Ka) for formic acid, with some participants asserting it is 1.8 x 10^(-4) while another claims it is 1.8 x 10^(-5). The discussion remains unresolved on this point.

Contextual Notes

Participants have not reached a consensus on the correct value of Ka, and there may be assumptions regarding the conditions under which the pH is calculated that are not explicitly stated.

geffman1
Messages
67
Reaction score
0

Homework Statement



hey guys, I've got a prob, i kinda know how to do this question but i can't get past the first step. i want to write an equilbrium expression by I am not sure what the chemical reaction is. any help would be good

Homework Equations



A solution of a weak acid, HCOOH, is made to a concentration of 0.689 mol / L. Calculate the pH of this solution.
Ka of HCOOH is 1.8 x 10-4.


The Attempt at a Solution

 
Physics news on Phys.org
The reaction of acetic acid in water (after actually dissolving) is a neutralization reaction. The water acts as a base. Also, for writing the Ka expression, the concentration of water does not effectively change. Since it is essentially constant, it is not written as part of the Ka expression.

Your reported value for Ka is one magnitude wrong. It should be 1.8*10^(-5), which is ten times smaller than the value you showed.
 
Last edited:
Borek said:
Actually question is about formic acid and Ka value of 1.8x10-4 is correct.

Check calculation of pH of a weak acid lecture.

Very Good. I understand.
 

Similar threads

  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 3 ·
Replies
3
Views
3K
Replies
6
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K