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...

Answer 1

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.