# How Do You Calculate the Required Amounts for Buffer Solutions?

• Taryn
In summary, to prepare a buffer solution with pH 5.30, dissolve acetic acid and sodium acetate in water. For each mole of sodium acetate, add 0.90mol to 1.0L of the solution. The resulting pH will be 3.5x10-8.
Taryn
Hey I have been having a lot of trouble in solving these problems and I have exams soon and I really don't know where to start, I know u aint meant to give the answers so instead would someone please go through all of the steps to finish this!
I really need some kinda help, This question was in a quiz and I was so confused as to wat I needa do... I am going to get help from a lecturer as well but inorder to study it I need some help please.

A buffer solution of pH = 5.30 can be prepared by dissolving acetic acid and sodium acetate in water. How many moles of sodium acetate must be added to 1.0 L of 0.25 M acetic acid to prepare the buffer?
The answer is meant to be 0.90mol but I have no Idea how to get to that!

Also one more We mix 100 mL of 0.20 M HBr and 50.0 mL of 0.40 M NaC1O. What is the pH of the resulting solution? Ka(HC1O) = 3.5 x 10-8

for this one i Wrote out the equation... and found that the concentration of HClO was 0.1333 or something like that... then I just had no idea where to go from there, I no that pH=pka- log(acid/base) but I just didnt no how to get to that point... I changed Ka(HClO) to pKa by using -log3.5 x 10- 8 but as I sed not sure where to go.

Taryn said:
A buffer solution of pH = 5.30 can be prepared by dissolving acetic acid and sodium acetate in water. How many moles of sodium acetate must be added to 1.0 L of 0.25 M acetic acid to prepare the buffer?
The answer is meant to be 0.90mol but I have no Idea how to get to that!
Do you know how to calculate the acidity consant for buffer solutions?

do you mean Kw and Kb coz I think so

Taryn said:
do you mean Kw and Kb coz I think so

I mean Ka perhaps you use different notantion? Anyway, the relationship between Ka and [H+ is given by;

$$K_{a} = [H^{+}] \times \frac{[\text{salt}]}{[\text{acid}]}$$

Where Ka is the acidity constant of the acid.

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I will give it a go... but i wat has me a little stumped is what happens to the pH, I obviously have to use that somewhere don't I?

wait a second I understand now I think, I will work it all out and if I have a problem I will just post it on this agen, thanks a lot.

Taryn said:
I will give it a go... but i wat has me a little stumped is what happens to the pH, I obviously have to use that somewhere don't I?

You'll need that to work out the hydrogen ion concentration, you'll also need to look up Ka for acetic acid.

okay sorry just one more question, I am a little confused... just coz wat will be the [H+], I wrote this, 1.8E-5=[H+] x [salt]/[o.25]

Then after I find the [salt] then I will just use n=c* volume right?
If you can't give me anymore help that's fine!

Taryn said:
okay sorry just one more question, I am a little confused... just coz wat will be the [H+], I wrote this, 1.8E-5=[H+] x [salt]/[o.25]
That looks good to me. You need to use you pH value to calculate the [H+], remember that;

$$pH = -log[H^{+}] \Leftrightarrow [H^{+}] = 10^{-pH}$$

Taryn said:
Then after I find the [salt] then I will just use n=c* volume right?
If you can't give me anymore help that's fine!
Yes, you would usually do that, but since the solution is dissolve in one litre, the calculation becomes n = c x 1 and therefore in this case; n = c

Do you follow?

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thanks very much that was heaps helpful and now I understand wat to do, don't know y I didnt think of that at the time.

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

A buffer solution helps to maintain a stable pH, or level of acidity, in a system. This is important because sudden changes in pH can have damaging effects on biological or chemical processes.

## 2. How does a buffer solution work?

A buffer solution contains a weak acid and its conjugate base, or a weak base and its conjugate acid. These components react with added acid or base, helping to prevent significant changes in the overall pH of the solution.

## 3. What is the ideal pH range for a buffer solution?

The ideal pH range for a buffer solution is typically within one unit above or below the pKa, or acid dissociation constant, of the weak acid or base in the solution. This allows for the most effective buffering capacity.

## 4. Can a buffer solution be used to adjust the pH of a solution?

While a buffer solution can help to maintain a stable pH, it is not typically used for adjusting the pH of a solution. Strong acids or bases are more commonly used for this purpose.

## 5. How can I prepare a buffer solution?

A buffer solution can be prepared by combining a weak acid or base with its conjugate base or acid in specific proportions. The exact concentrations and proportions will depend on the desired pH and the pKa of the components.

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