8) Four litres of 0.4M 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer of pH 7.2 are required. Available in the laboratory are 10M...
To prepare 4 L of 0.4 M HEPES buffer of pH 7.2, we'll need to calculate the amount of HEPES and the volume of 10M NaOH required.
First, let's calculate the amount of HEPES required:
Molarity (M) = moles/volume (L)
Rearranging the equation we get:
moles = Molarity*volume
moles = 0.4 M * 4 L = 1.6 moles
HEPES has a molecular weight of 260.36 g/mol. Therefore, we can calculate the required mass of HEPES:
Mass (g) = Moles * Molecular weight
Mass (g) = 1.6 moles * 260.36 g/mol = 416.576 g
Now let's calculate the volume of 10M NaOH required to adjust the pH:
The pH of HEPES buffer is determined by the ratio of HEPES/base. HEPES acts as a weak acid, and we need to add a strong base to adjust the pH. Since NaOH is commonly used as a base, we'll use that.
To calculate the volume of NaOH required, we'll use the following equation:
[H+] = 10^(-pH)
[H+] = 10^(-7.2) = 6.31 x 10^(-8) M
We need to neutralize this with the same concentration of NaOH, so:
[H+] = [OH-] = 6.31 x 10^(-8) M
Using the equation:
Moles = Molarity * Volume
Moles = 6.31 x 10^(-8) M * 4 L = 2.524 x 10^(-7) moles
To calculate the volume of 10M NaOH required:
Volume (L) = Moles/Molarity
Volume (L) = 2.524 x 10^(-7) moles / 10 M = 2.524 x 10^(-8) L = 25.24 µL
So, 416.576 g of HEPES and 25.24 µL of 10M NaOH are required to prepare 4 L of 0.4M HEPES buffer of pH 7.2.
To prepare four liters of 0.4M HEPES buffer of pH 7.2 using the available 10M HEPES stock solution, follow these steps:
Step 1: Calculate the required volume of 10M HEPES stock solution.
The desired concentration of the final buffer is 0.4M. Since the available stock solution is 10M, we can determine the volume of stock solution needed using the formula:
Volume of stock solution = (Desired concentration * Final volume) / Stock solution concentration
Plugging in the values:
Volume of stock solution = (0.4M * 4L) / 10M
Volume of stock solution = 0.16L or 160mL
Therefore, we need 160mL of the 10M HEPES stock solution.
Step 2: Calculate the remaining volume of water needed.
To prepare a total volume of four liters of buffer, we subtract the volume of the stock solution from the final volume:
Remaining volume of water = Final volume - Volume of stock solution
Remaining volume of water = 4L - 0.16L
Remaining volume of water = 3.84L
Therefore, you will need 3.84 liters of water.
Step 3: Mix the stock solution and water.
In a suitable container, add the calculated volume of 10M HEPES stock solution (160mL) and the remaining volume of water (3.84L). Stir or mix gently to ensure complete distribution.
You have now prepared four liters of 0.4M HEPES buffer with a pH of 7.2 using the available 10M HEPES stock solution.