# How Do You Prepare a 40 L Phosphate Buffer with pH 6.9?

• Eshi
The initial value of [HA] at 1M is 40L. To get to a final value of .0500M, you must dilute 1/20 = 2L.
Eshi

## Homework Statement

Describe the preparation of 40 L of 0.0500M phosphate buffer, pH 6.9 starting with 1M solutions of KH2PO4 and K2HPO4. pKa= 7.2

## Homework Equations

pH= pKa + log[A-]/[HA]3. The Attempt at a Solution [/b

6.9=7.2 + log[A-]/[HA]
-0.3= log[A-]/[HA]
[A-]/[HA]= 0.50

0.5[HA]= [A-]
0.5[HA]+1[A-] = 1.5

0.5/1.5 = 0.33 = 33% [HA]0.05 mol/L x 40L = 2 mol HA
2 mol x 1L/mol = 2L HA2 mol x 0.33= 0.66 mol A-
0.66 mol x 1L/mol = 0.66 L A-2L HA + 0.66L A- = 2.66 <---Edit: 2.66 L of acid/base

40L-2.66L= add 37.34 L water to make the 40L total.
I was told by someone that this solution is incorrect. Any suggestions why?

Last edited:
Eshi said:
2L HA + 0.66L A- = 2.66

Earlier you wrote you need 2 moles, here you have 2.66.

Not that I am sure I understand precisely your working in other places.

Last edited by a moderator:
In the equation pH=pKa+log[A]/[HA], the ratio of the log value must be 10^-3=.5. Therefore, [HA] must be double [A].

## What is an acid/base buffer reaction?

An acid/base buffer reaction is a chemical reaction that involves the combination of an acid and a base to form a buffer solution. A buffer solution is a solution that resists changes in pH when small amounts of acid or base are added.

## What is the purpose of an acid/base buffer reaction?

The purpose of an acid/base buffer reaction is to maintain a stable pH in a solution. This is important in various biological and industrial processes, as well as in laboratory experiments, where a specific pH is necessary for optimal functioning of enzymes or other substances.

## How does an acid/base buffer reaction work?

An acid/base buffer reaction works by combining a weak acid and its conjugate base (or a weak base and its conjugate acid) in a solution. The weak acid or base will partially dissociate, releasing H+ or OH- ions respectively. This helps to neutralize any added acid or base, maintaining the overall pH of the solution.

## What factors affect the effectiveness of an acid/base buffer reaction?

The effectiveness of an acid/base buffer reaction can be affected by the concentration of the buffer components, the strength of the acid and base, and the pH of the solution. Additionally, temperature and the presence of other ions or substances can also impact the effectiveness of a buffer solution.

## What are some real-world applications of acid/base buffer reactions?

Acid/base buffer reactions have many real-world applications, such as in the production of pharmaceuticals, food and beverage production, and in medical procedures to maintain a stable pH in the body. They are also important in environmental processes, such as maintaining a stable pH in bodies of water to support aquatic life.

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