Question

You need to make 50 mL of a 25 mM Tris buffer that has a pH of 8.40. Show calculations for and describe how you would make it if you had access to: •A) Solid Tris acid (Tris HCl) and solid Tris base •B) Solid Tris acid and 1.0 M NaOH •C) Solid Tris base and 1.0 M HCl

Answer 1

Volume of TRIS buffer = 50 mL = 50 mL x (1L / 1000 mL) = 0.050 L

Concentration of TRIS buffer = 25 mM = 25 mM x (1 M / 1000 mM) = 0.025 M

Hence moles of TRIS required to make 50 mL of a 25 mM Tris buffer = M x V = 0.025 M x 0.050 L = 0.00125 mol

Molecular mass of TRIS (2-amino-2-hydroxymethyl-propane -1,3-diol) = 121.14 g/mol

Hence mass of TRIS required = 0.00125 mol x 121.14 g/mol = 0.1514 g

(A) We need to take Solid Tris acid (Tris HCl) and solid Tris base in such a proportion that they would contain 0.1514 g of TRIS.

(B) Take solid tris acid containing 0.1514 g TRIS and add 1.0 M NaOH and then dilute to get the desired volume and pH of 8.40.

(C)  Take solid tris base containing 0.1514 g TRIS and add 1.0 M HCl and then dilute to get the desired volume and pH of 8.40.