Calculate how you would make 0.5L of a 0.5M (500mM) acetate buffer at a pH of 4.7. Available is sodium acetate and glacial acetic acid.
pH=4.7
pKa of acetic acid=4.76
Not sure if I did this next part right:
4.7=4.76 + log [base]/[acid]
-0.06= log [base]/[acid]
10^-0.06= [base]/[acid]
0.87=[base]/[acid]
0.5= base + acid and
0.87= [base]/[acid]
0.87acid + acid = 0.5
acid + acid = 0.575
I guessed on this part trying to follow along with other examples
10^0.575 = 3.7 ~ 4
acid= 4
0.5= base = 4
base= -3.5
I am really stuck on what to do next...I would appreciate any help!
Right. Up to
a + 0.87a = 0.5 but then you went in the wrong direction.
If a + 0.87a = 0.5 then
1.87a = 0.5 and
(acid) - 0.5/1.87 = 0.267 M and
(base) = 0.5-0.267 = 0.233 M.
So M acid = 0.267 = mol/L. You know L and M, solve for mols and convert to grams.
Do the same for M base.
What is the concentration of HOAc in a 0.8M Acetate buffer, pH 2.00?
(pKa for Acetic acid is 4.77)
To make a 0.5M (500mM) acetate buffer at a pH of 4.7 using sodium acetate and glacial acetic acid, you can follow these steps:
Step 1: Determine the ratio of the concentration of the conjugate base (sodium acetate) to the concentration of the acid (acetic acid) required to achieve the desired pH.
The Henderson-Hasselbalch equation is given by:
pH = pKa + log([base]/[acid])
Given that the pH is 4.7 and the pKa of acetic acid is 4.76, substitute these values into the equation:
4.7 = 4.76 + log([base]/[acid])
Rearrange the equation:
log([base]/[acid]) = 4.7 - 4.76
log([base]/[acid]) = -0.06
Calculate the antilog of -0.06:
[base]/[acid] = 10^(-0.06)
[base]/[acid] = 0.87
Step 2: Determine the total volume of the buffer solution.
You want to make 0.5 L of the buffer solution.
Step 3: Calculate the amount of acid (acetic acid) required.
Since 0.87 is the mole ratio of the base (sodium acetate) to acid (acetic acid), assume a value for the acid concentration (let's call it x). This means the base concentration is 0.87x.
Given that the total volume is 0.5 L, you can set up the equation:
x + 0.87x = 0.5
Solve for x:
1.87x = 0.5
x = 0.5/1.87
x ≈ 0.267 M
Therefore, the concentration of acetic acid required is approximately 0.267 M.
Step 4: Calculate the amount of base (sodium acetate) required.
The concentration of the base (sodium acetate) is 0.87 times the concentration of the acid (acetic acid):
0.87 * 0.267 M = 0.232 M
Therefore, the concentration of sodium acetate required is 0.232 M.
Step 5: Determine the amount of each component required.
To calculate the amount of each component required, use the formula:
Amount (in moles) = concentration (in M) × volume (in L)
For acetic acid:
Amount of acetic acid = 0.267 M × 0.5 L ≈ 0.134 moles
For sodium acetate:
Amount of sodium acetate = 0.232 M × 0.5 L ≈ 0.116 moles
Step 6: Convert the amounts of each component to grams.
To convert from moles to grams, use the molecular weight of each compound.
The molecular weight of acetic acid (CH3COOH) is approximately 60.05 g/mol.
The molecular weight of sodium acetate (CH3COONa) is approximately 82.03 g/mol.
For acetic acid:
Mass of acetic acid = 0.134 moles × 60.05 g/mol ≈ 8.043 g
For sodium acetate:
Mass of sodium acetate = 0.116 moles × 82.03 g/mol ≈ 9.517 g
So, to make a 0.5L of a 0.5M (500mM) acetate buffer at a pH of 4.7, you would need approximately 8.043 grams of glacial acetic acid and 9.517 grams of sodium acetate. Dissolve both components in water and bring the final volume up to 0.5 L.
To make a 0.5L acetate buffer at a pH of 4.7, you'll need to follow these steps:
Step 1: Determine the concentration of the buffer components
The pH of the buffer is determined by the ratio of the concentration of the acetate ion (base) to acetic acid (acid). Since you want a concentration of 0.5M (500mM), you need to divide it into the base and acid components. Let's call the base concentration "x" and acid concentration "y".
Step 2: Calculate the ratio of base to acid using the Henderson-Hasselbalch equation
The Henderson-Hasselbalch equation relates the pH, pKa, and the concentration of base and acid in a buffer solution. The equation is:
pH = pKa + log10 [base]/[acid]
In this case, the pH is 4.7, and the pKa of acetic acid is 4.76. Rearranging the equation:
log [base]/[acid] = pH - pKa
Plugging in the values:
log [base]/[acid] = 4.7 - 4.76
log [base]/[acid] = -0.06
To solve for [base]/[acid], we take the antilog of -0.06:
[base]/[acid] = 10^-0.06
[base]/[acid] = 0.87
So, the ratio of base to acid is 0.87.
Step 3: Calculate the actual concentrations of base and acid
Remember that the total volume of the buffer is 0.5L. Therefore, you can set your equation:
x + y = 0.5
Also, the ratio of base to acid is given by:
x/y = 0.87
Now you have a system of two equations in two unknowns. You can solve this system to find the actual concentrations of base (x) and acid (y). You can use substitution or elimination methods to solve the system.
Here's one way to solve the system:
From the second equation, we can rewrite it as:
x = 0.87y
Substituting this into the first equation:
0.87y + y = 0.5
1.87y = 0.5
y = 0.5 / 1.87
y = 0.267 M (acid concentration)
Now, substitute the acid concentration (y) into the second equation to find the base concentration (x):
x = 0.87 * 0.267
x = 0.232 M (base concentration)
So, to make a 0.5L acetate buffer at a pH of 4.7, you need to mix 0.232 moles of sodium acetate (base, approximately 13.578g) and 0.267 moles of glacial acetic acid (acid, approximately 19.243g) together in 0.5L of water.