# Anticipated pH of Buffer Solution ( )

• erjkism
In summary, the process for finding the pH of a buffer solution after adding 100 mL of 0.0983 M HCl is to first calculate the initial moles of CH3COOH and CH3CO2- based on the given concentrations and volume. Then, using the equilibrium expression and the given Ka value, solve for [H3O+] and use the pH formula to find the final pH. The student in the conversation had trouble with their calculations at first but eventually got the correct answer.
erjkism
[SOLVED] Anticipated pH of Buffer Solution (urgent!)

## Homework Statement

Can someone verify my process here? i did a lab where i had 100 mL CH3COOH/CH3CO2- buffer solution. I have to find the pH if 100 mL of 0.0983 M HCl is added to it. In the lab i got pH of 1.72

2. Homework Equations

[H3O+][CH3CO2-]
Ka= ---------------------
[CH3COOH]

Ka : 1.8x10-5
initial moles CH3COOH: 0.00996
Initial moles CH3CO2-: 0.0100
moles H+ in 100 mL 0.0983 M HCl: 0.00983

## The Attempt at a Solution

It's my understanding that the mole ratio of H+/CH3CO2- is one to one.
Next i think i do this:

moles CH3COOH = 0.00996 + 0.00983 = 0.0198 moles
moles CH3CO2-= 0.0100- 0.00983= 0.00017 moles

concentration CH3COOH= 0.0198 moles/(0.200 L) = 0.099 M
concentration CH3CO2-= 0.00017/(0.200 L) = 0.00085 M

Then by rearranging the equilibrium expression i can solve for [H3O+].
[H3O+]=(1.8x10-5)(0.099M) / (0.00085) = 0.00212 M

pH= -log(0.00212M) = 2.67

is that how am supposed to go about doing this? because my other lab values are very strange. for instance, i keep getting a pH of 4.7 after adding 5, 10, and 20 mL of HCl to it.

k i finally got the answer thanks anyone who looked at it tho

Yes, your process for calculating the pH of the buffer solution after adding HCl is correct. However, it is important to note that the pH of a buffer solution is affected by the ratio of the concentrations of the conjugate acid and base, not just the concentrations themselves. In your calculation, you assumed that the concentrations of CH3COOH and CH3CO2- were equal, but this may not have been the case in the actual lab experiment. It is possible that the initial concentrations of the buffer components were not exactly 0.1 M, or that there were other factors that affected the equilibrium. This could explain why your calculated pH values do not match the experimental values.

In order to verify your process and results, it would be helpful to double-check your initial concentrations and the volumes of HCl added in the experiment. It may also be useful to compare your results with those of your classmates or with the expected pH values for a CH3COOH/CH3CO2- buffer solution. Overall, your approach to solving this problem is correct, but it is important to consider all factors that may affect the equilibrium in order to obtain accurate results.

## 1. What is the purpose of a buffer solution?

A buffer solution is used to maintain a constant pH in a solution, even when small amounts of acid or base are added. It is important in many biological and chemical processes where maintaining a specific pH is necessary for proper function.

## 2. How is the anticipated pH of a buffer solution calculated?

The anticipated pH of a buffer solution is calculated using the Henderson-Hasselbalch equation, which takes into account the concentration of the weak acid and its conjugate base, as well as the dissociation constant (pKa) of the acid. The equation is pH = pKa + log([base]/[acid]).

## 3. What factors can affect the anticipated pH of a buffer solution?

The anticipated pH of a buffer solution can be affected by changes in temperature, concentration of the acid and base, and the pKa of the acid. Other factors such as impurities or contamination in the solution can also alter the anticipated pH.

## 4. How can the anticipated pH of a buffer solution be adjusted?

The anticipated pH of a buffer solution can be adjusted by changing the concentration of the acid or the base. Adding more of the conjugate acid or base can also help to adjust the pH. Additionally, changing the pKa of the acid by adding a different weak acid can also alter the anticipated pH.

## 5. Can a buffer solution have a pH value outside of its anticipated range?

Yes, it is possible for a buffer solution to have a pH value outside of its anticipated range. This can occur if there is a significant change in the concentrations of the acid or base, or if the solution becomes contaminated. However, a well-made buffer solution should be able to resist large changes in pH and maintain its anticipated range.

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