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.
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