# Acid Mixture pH Problem: Calculating Solution pH with CH3COOH, CH3COONa, and HCl

• terryds
In summary: So moles of HCl will be exhausted first and then only the reaction will proceed to produce more CH3COOH.Now you can use the Henderson-Hasselbalch equation to get the pH of the solution. In summary, the solution to the given problem involves calculating the pH of a mixture of 30 mL of 0.2 M CH3COOH, 60 mL of 0.1 M CH3COONa, and 10 mL of 0.1 M HCl. Using the Henderson-Hasselbalch equation, the answer is found to be 5 - log 1.4. This is because the presence of CH3COONa and HCl shifts the equilibrium of the dissociation
terryds

## Homework Statement

30 mL CH3COOH 0.2 M is mixed with 60 ml CH3COONa 0.1 M and then added with 10 mL HCl 0.1 M, then what is the pH of the solution ? (Ka = 10-5)

A. 3
B. 5 - log 1.4
C. 5 - log 2
D. 4 - log 1.4
E. 5 + log 2

## Homework Equations

[H+] = Ka * [HX] / [X- ] ---- buffer
[H+] = ([H+]V1 + [H+]V2) / (V1 + V2) ---- mixture

## The Attempt at a Solution

The hydrogen molarity from the buffer is 10^-5 * 6 / 6 = 10^-5

Hydrogen concentration of the mixture = (10^-5 * 90 + 10^-1 * 10) / ( 90 + 10 ) = (9 * 10^-4 + 1 ) / 100 = 9 * 10^-6 + 10^-2

pH = - log ( 9 * 10^-6 + 10^-2 ) which doesn't appear in the options..

Here is what I did:

First off, we can neglect the H+ ions provided by the weak acid to the solution as they are negligible compared to the H+ provided by the HCl.
Then the concentration can be replaced with the moles, because the entire mixture is in the same solution and the volume terms will get cancelled.
On doing so, we get 4 + log 6. This is pretty close to the value of option (c).

CrazyNinja said:
Here is what I did:

First off, we can neglect the H+ ions provided by the weak acid to the solution as they are negligible compared to the H+ provided by the HCl.
Then the concentration can be replaced with the moles, because the entire mixture is in the same solution and the volume terms will get cancelled.
On doing so, we get 4 + log 6. This is pretty close to the value of option (c).

The answer is B. 5 - log 1,4
But, the explanation of the answer is just 10^-5 * 7 / 5 which is very confusing...
I really don't get it..

The solution to the answer has assumed that the CH3COONa reacts with the HCl providing you with more CH3COOH. That is not completely correct. The salt will completely dissociate, but not all the CH3COO(minus) ions will interact with HCl to give CH3COOH.

CrazyNinja said:
The solution to the answer has assumed that the CH3COONa reacts with the HCl providing you with more CH3COOH. That is not completely correct. The salt will completely dissociate, but not all the CH3COO(minus) ions will interact with HCl to give CH3COOH.

Why not all the ions will interact? How do you do the problem?

OK wait. I am sorry. the answer given is correct. It is (b).

This is because there exists an equilibrium for the dissociation of CH3COOH.

CH3COOH ↔ CH3COO(-) + H(+)

Now if there was no HCl or CH3COONa, the dissociation would proceed without any hindrance. But the prescence of these two generates CH3COO(-) ions and H(+) ions. Now these will shift the equlibrium reaction (use Le-Chatlier's principle). Thus CH3COOH will be produced. Obviously in the reaction, HCl is the limiting reagent.

terryds

## 1. What is the purpose of calculating solution pH with CH3COOH, CH3COONa, and HCl?

The purpose of this calculation is to determine the overall pH of a mixture containing these three acids, which can be used to understand the acidity or basicity of the solution and its potential impact on chemical reactions.

## 2. What is the importance of knowing the pH of the acid mixture?

The pH of the acid mixture is important for a variety of reasons. It can affect the reactivity and stability of the solution, as well as the effectiveness of any chemical reactions that may take place. It can also have an impact on the safety and handling of the solution.

## 3. How do you calculate the pH of an acid mixture?

To calculate the pH of an acid mixture, you need to know the concentrations of each acid in the solution, as well as their individual dissociation constants. You can then use the Henderson-Hasselbalch equation to calculate the pH based on these values.

## 4. What are the potential challenges in calculating the pH of an acid mixture?

One potential challenge is accurately measuring the concentrations of each acid in the solution. This can be difficult if the acids are in a solid form or if they are mixed with other substances. Another challenge is determining the correct dissociation constants to use in the Henderson-Hasselbalch equation.

## 5. How can the pH of an acid mixture be adjusted?

The pH of an acid mixture can be adjusted by adding either an acid or a base to the solution. This will change the overall concentration and proportion of the different acids, which will in turn affect the pH. The specific acid or base added will depend on the desired direction of the pH change.

• Biology and Chemistry Homework Help
Replies
3
Views
2K
• Biology and Chemistry Homework Help
Replies
16
Views
2K
• Biology and Chemistry Homework Help
Replies
4
Views
1K
• Biology and Chemistry Homework Help
Replies
4
Views
1K
• Biology and Chemistry Homework Help
Replies
7
Views
3K
• Biology and Chemistry Homework Help
Replies
2
Views
2K
• Biology and Chemistry Homework Help
Replies
8
Views
2K
• Biology and Chemistry Homework Help
Replies
20
Views
2K
• Biology and Chemistry Homework Help
Replies
4
Views
3K
• Biology and Chemistry Homework Help
Replies
3
Views
2K