# Percent Dissociation of Acetic Acid

• Teemo
In summary: So, it is the same formula, but in different form.In summary, we can calculate the pH of a solution containing 11% ionized acetic acid at 25 degrees Celsius by using the Ka value and the degree of dissociation squared. The formula is called the Ostwald dilution law and can be derived from the equilibrium constant expression.
Teemo

## Homework Statement

In a particular solution, acetic acid is 11% ionized at 25 degrees Celsius. Calculate the pH of the solution and the mass of acetic acid dissolved to yield 1.00 L of solution.
Ka of CH3CO2H: 1.8x10^(-5)

## Homework Equations

Ka=([CH3CO2-][H3O+])/[CH3CO2H]
pH=-log[H3O+]

## The Attempt at a Solution

I'm not sure how exactly I should begin, as I do not know the concentration of the acetic acid, so I don't know how to solve for [H+]

Last edited:
There are two equations that you have not listed yet. One will describe 11% dissociation. The other will be a direct effect of the dissociation stoichiometry - what can you tell about amounts of H+ and CH3COO- present in the solution?

Teemo said:

## Homework Statement

In a particular solution, acetic acid is 11% ionized at 25 degrees Celsius. Calculate the pH of the solution and the mass of acetic acid dissolved to yield 1.00 L of solution.
Ka of CH3CO2H: 1.8x10^(-5)

## Homework Equations

Ka=([CH3CO2-][H3O+])/[CH3CO2H]
pH=-log[H3O+]

## The Attempt at a Solution

I'm not sure how exactly I should begin, as I do not know the concentration of the acetic acid, so I don't know how to solve for [H+]
Suppose you let x represent the number of moles of acetic acid dissolved in 1 liter of solution. After the acetic acid ionizes 11%, in terms of x, how many moles of acetic acid are left. How many moles of CH3CO2- are formed, and how many moles of H3O is formed? What are the new molar concentrations of these three species? Using Ka, what is the value of x?

Right, I have the answer key which writes that the formula is C=Ka/(degree dissociation)^2, however I'm not sure what this formula is called and why the degree of dissociation is squared.

Chestermiller said:
Suppose you let x represent the number of moles of acetic acid dissolved in 1 liter of solution. After the acetic acid ionizes 11%, in terms of x, how many moles of acetic acid are left. How many moles of CH3CO2- are formed, and how many moles of H3O is formed? What are the new molar concentrations of these three species? Using Ka, what is the value of x?

How exactly would this work? Would it be ([.11x][.11x])/[.89x], where x is original concentration of acetic acid?

Teemo said:
How exactly would this work? Would it be ([.11x][.11x])/[.89x], where x is original concentration of acetic acid?
Yes.

Teemo said:
Right, I have the answer key which writes that the formula is C=Ka/(degree dissociation)^2, however I'm not sure what this formula is called and why the degree of dissociation is squared.

It is an approximated version of the http://en.wikipedia.org/wiki/Ostwald_dilution_law

You should be able to do derive it by yourself using hints that were already posted.

Thanks so much :D, I guess my answer key is wrong haha.

Your answer key is correct, have you checked the wikipedia page I linked to? It derives exactly the same formula, just uses it to calculate degree of dissociation, not C.

## What is the percent dissociation of acetic acid?

The percent dissociation of acetic acid refers to the percentage of acetic acid molecules in a solution that have dissociated into hydrogen ions (H+) and acetate ions (CH3COO-). It is a measure of the strength of an acid and is typically expressed as a decimal or percentage.

## How is the percent dissociation of acetic acid calculated?

The percent dissociation of acetic acid can be calculated by taking the concentration of hydrogen ions (H+) in the solution and dividing it by the initial concentration of acetic acid. This value is then multiplied by 100 to get the percentage.

## What factors can affect the percent dissociation of acetic acid?

The percent dissociation of acetic acid can be affected by factors such as temperature, concentration of the acid, and the presence of other substances in the solution. Higher temperatures and lower concentrations can increase the percent dissociation, while the presence of certain substances, such as strong bases, can decrease it.

## Why is the percent dissociation of acetic acid important in chemistry?

The percent dissociation of acetic acid is important in chemistry because it can help determine the strength of an acid and its behavior in a solution. It is also a key factor in understanding acid-base reactions and their equilibrium constants.

## How is the percent dissociation of acetic acid used in the real world?

The percent dissociation of acetic acid has many practical applications, such as in the production of vinegar and other food products. It is also used in industries such as pharmaceuticals and cosmetics to control the acidity of products. In addition, it is an important concept in environmental chemistry, as it can affect the pH of natural water sources and the behavior of pollutants.

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