Describe and show all calculations on how you would prepare

Describe and show all calculations on how you would prepare 2.5 liters of 0.1 M TRIS-HCl buffer, pH 8.5, starting with TRIS powder and a bottle of hydrochloric acid. The molecular weight of TRIS is 121.1, and the pK_a is 8.3. Remember that HCl is a liquid of 12.1 Molar.

Solution

Buffer TRIS/TRIS-HCl (weak base/conjugate acid)

pH = 8.5

pKa = 8.3

Using Hendersen-Hasselbalck equation,

pH = pKa + log(base/acid)

8.5 = 8.3 + log(TRIS/TRIS-HCl)

(TRIS) = 1.6(TRIS-HCl)

we have,

(TRIS) + (TRIS-HCl) = 0.1 M x 2.5 L = 0.25 moles

1.6(TRIS-HCl) + (TRIS-HCl) = 0.25 moles

(TRIS-HCl) = 0.25 moles/2.6 = 0.096 moles

Volume of HCl soluton needed = 0.096 moles x 1000/12.1 M = 7.934 ml

mass of TRIS needed = 0.1 M x 2.5 L x 121.1 g/mol = 30.275 g