How would you prepare 30 mL of acetic acid/acetate buffer solution of pH = 5.06?. Assumeyou have 0.1M solutions of both acetic acid and sodium acetate {pKa(acetic acid) = 4.76}
If we knew the molarity you wanted for the buffer we could calculate it. I suppose not knowing the M you must make it up and measure.
So I would take 10 mL of the acetate stock and 10 mL of the acid stock, mix, and add drop wise and with stirring, NaOH until the pH meter reads 5.00. Then add water to make 30 mL, mix, bottle, stopper, etc.
To prepare a 30 mL acetic acid/acetate buffer solution with a pH of 5.06, you will need to calculate the amounts of acetic acid and sodium acetate needed. Here are the step-by-step instructions:
Step 1: Calculate the acid-to-conjugate base ratio
The Henderson-Hasselbalch equation can be used to calculate the acid-to-conjugate base ratio. It is given by:
pH = pKa + log([A-]/[HA])
Where:
pH = 5.06 (desired pH)
pKa = 4.76
[A-] = concentration of conjugate base (sodium acetate)
[HA] = concentration of acid (acetic acid)
To find the ratio [A-]/[HA], rearrange the Henderson-Hasselbalch equation:
[A-]/[HA] = 10^(pH - pKa)
Substituting the values:
[A-]/[HA] = 10^(5.06 - 4.76)
[A-]/[HA] = 10^0.3
[A-]/[HA] = 2
This means that you will need to have a 2:1 ratio of acetic acid to sodium acetate in the buffer.
Step 2: Calculate the amounts of acetic acid and sodium acetate needed
Since you have a 0.1 M solution of both acetic acid and sodium acetate, you can use the formula:
Amount (in moles) = concentration (in M) × volume (in L)
Let's assume x represents the amount (in moles) of acetic acid needed. Since the ratio of acetic acid to sodium acetate is 2:1, you will need to use 2x moles of sodium acetate.
Amount of acetic acid = 0.1 M × x mole × 0.03 L
Amount of sodium acetate = 0.1 M × 2x mole × 0.03 L
Step 3: Set up the equation using the dissociation of acetic acid
Acetic acid, CH3COOH, dissociates into CH3COO- and H+. The concentration of H+ can be calculated using the equation:
[H+] = Ka × [HA]/[A-]
Given that pKa = 4.76, we can calculate Ka:
Ka = 10^(-pKa)
Ka = 10^(-4.76)
Since [HA] = x (amount of acetic acid) and [A-] = 2x (amount of sodium acetate), we substitute these values into the equation to get:
[H+] = 10^(-4.76) × x/ (2x)
Step 4: Calculate the pH using [H+]
Given that pH = 5.06, we can use the equation:
pH = -log[H+]
Substituting the value of [H+] into the equation:
5.06 = -log(10^(-4.76) × x/ (2x))
Step 5: Solve the equation for x
To find the value of x, you need to solve the equation from Step 4.
5.06 = -log(10^(-4.76) × x/ (2x))
First, simplify the equation:
5.06 = -log(10^(-4.76)/2)
Next, take the antilog of both sides:
10^(5.06) = 10^(-4.76)/2
Finally, solve for x:
x = (10^(-4.76)/2) × 10^(5.06)
Step 6: Calculate the actual amounts of acetic acid and sodium acetate
Using the value of x calculated in Step 5, you can find the actual amounts of acetic acid and sodium acetate.
Amount of acetic acid = 0.1 M × x mole × 0.03 L
Amount of sodium acetate = 0.1 M × 2x mole × 0.03 L
These are the step-by-step instructions to prepare a 30 mL acetic acid/acetate buffer solution with a pH of 5.06.
To prepare a 30 mL acetic acid/acetate buffer solution with a pH of 5.06, you will need to calculate the amount of acetic acid and sodium acetate required. The buffer will work because the pKa of acetic acid is close to the desired pH, allowing it to function effectively.
Here are the steps to prepare the buffer solution:
1. Determine the ratio of acetic acid to acetate needed:
- Since acetic acid and sodium acetate will react in an equimolar ratio to form the buffer, the ratio of their concentrations in the final solution will be 1:1.
2. Calculate the concentration of acetic acid and acetate needed:
- The required concentration of the buffer is not specified, so let's assume it to be 0.1 M, as mentioned in the question.
- Since the concentrations of acetic acid and sodium acetate are the same, you will need 0.1 M of each substance.
3. Calculate the moles of acetic acid and acetate needed:
- Moles = Concentration × Volume (in liters)
- Since the total volume desired is 30 mL or 0.03 L:
- Moles of acetic acid = 0.1 M × 0.03 L = 0.003 moles
- Moles of sodium acetate = 0.1 M × 0.03 L = 0.003 moles
4. Convert the moles to grams of acetic acid and sodium acetate:
- The molecular weight of acetic acid (CH3COOH) is approximately 60.05 g/mol, and the molecular weight of sodium acetate (CH3COONa) is approximately 82.03 g/mol.
- Grams of acetic acid = Moles × Molecular Weight = 0.003 moles × 60.05 g/mol = 0.18015 g
- Grams of sodium acetate = Moles × Molecular Weight = 0.003 moles × 82.03 g/mol = 0.24609 g
5. Dissolve the calculated amounts of acetic acid and sodium acetate:
- Measure 0.18015 g of acetic acid and 0.24609 g of sodium acetate accurately using a balance.
- Dissolve each solid in water separately, using minimal volume.
- Transfer both the solutions to a clean glass container.
6. Adjust the volume and pH of the buffer solution:
- Add water to the acetic acid solution and/or sodium acetate solution to adjust the total volume to exactly 30 mL.
- Measure the initial pH of the solution using a pH meter.
- Adjust the pH if necessary by adding small amounts of either acetic acid or sodium acetate solution until the desired pH of 5.06 is achieved. Measure the pH after each addition using a pH meter.
Remember to take necessary safety precautions, such as wearing gloves and goggles, while handling these chemicals. Always work in a well-ventilated area.