# Find the Error: Calculating pH of 0.5L Diluted HA Solution

• Jzhang27143
In summary, a solution with a volume of 0.5 liters and a concentration of 1.5 M is prepared by adding 0.75 moles of a weak acid HA to water. The equilibrium concentration of H3O+ is found to be 0.34 M, which results in a pH of 1.1 when the solution is diluted to a final volume of 2.0 liters. However, the correct answer is 0.8 and it is unclear where the mistake was made.If the question were changed to preparing 2 liters of solution using 0.75 moles of HA, the approach would be similar. The only difference would be that the initial concentration would be 0.375 M
Jzhang27143
this type of question should go into homework section
You prepare 0.5 liters of a solution by adding 0.75 moles of a weak acid HA to water. For HA, Ka = 10^-1 Finally you dilute this solution to a final volume of 2.0 liters. What is the pH of the diluted solution?

My solution is this. [HA] = .75 mol /.5 L = 1.5 M. HA + H2O -> H3O+ + A-. If x is the equilibrium concentration of H3O+, x^2 /(1.5 - x) = 10^-1 so solving for x gives x = 0.34 M = [H3O+].

Moles of H3O+ must be 0.34M * 0.5 L = 0.17 mol. When the new volume is 2.0 L, [H3O+] = 0.085M so the pH = 1.1. However, the correct answer to this is 0.8. Where did I go wrong?

What if the question were "you prepare 2 liters of solution using 0.75 moles of a weak acid HA"? How would you approach it? Any reason why it should be a different problem from the one you tried to solve?

## 1. What is the purpose of calculating the pH of a diluted HA solution?

The purpose of calculating the pH of a diluted HA solution is to determine its acidity or basicity. This information is important in various scientific experiments and processes, as it can affect the outcome of chemical reactions.

## 2. How do you calculate the pH of a 0.5L diluted HA solution?

The pH of a 0.5L diluted HA solution can be calculated using the formula pH = -log[H+], where [H+] is the hydrogen ion concentration. This concentration can be found by dividing the number of moles of the solute (HA) by the total volume of the solution (0.5L).

## 3. What is HA in the context of calculating pH?

HA refers to the acid in the solution and is typically represented by a chemical formula. For example, if the solution is hydrochloric acid (HCl), then HA would be represented as HCl in the calculation of pH.

## 4. Why is it important to dilute the HA solution before calculating its pH?

Diluting the HA solution is important in order to ensure that the concentration of the solution is within a measurable range. If the solution is too concentrated, it can be corrosive and difficult to handle. Dilution also allows for more accurate measurements and calculations.

## 5. What factors can affect the accuracy of the pH calculation for a diluted HA solution?

The accuracy of the pH calculation for a diluted HA solution can be affected by various factors such as the accuracy of the measurements, the purity of the solute, and the temperature of the solution. It is important to ensure precise and consistent measurements and to use high-quality, pure chemicals for the most accurate results.

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