Solving pH of an Aqueous Solution of Weak Acid HCOOH

Click For Summary
SUMMARY

The discussion focuses on calculating the pH of a 0.689 mol/L aqueous solution of formic acid (HCOOH) with a dissociation constant (Ka) of 1.8 x 10-4. Participants clarify the equilibrium expression for the dissociation of HCOOH in water, emphasizing that water's concentration remains constant and is not included in the Ka expression. A correction was made regarding the reported Ka value, confirming that 1.8 x 10-4 is indeed accurate for formic acid. The conversation highlights the importance of understanding weak acid dissociation in pH calculations.

PREREQUISITES
  • Chemical equilibrium concepts
  • Understanding of weak acid dissociation
  • Knowledge of pH calculations
  • Familiarity with the acid dissociation constant (Ka)
NEXT STEPS
  • Study the equilibrium expression for weak acids
  • Learn how to calculate pH from Ka values
  • Explore the properties of formic acid and its applications
  • Review lecture materials on weak acid pH calculations
USEFUL FOR

Chemistry students, educators, and anyone involved in acid-base chemistry who seeks to deepen their understanding of weak acid behavior and pH calculations.

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
2K
  • · 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