Prepare 50 mL of TRIS buffer at strength of 0.1 M and at a pH of 7.5 using Tris, 1 M HCl and water.
TRIS pKa: 8.3
TRIS formula weight: 121.1 g/mol
50 mL of TRIS buffer at strength of 0.1 M
we have,
pH = pKa + log [A]/[HA]
at a pH of 7.5 , TRIS pKa: 8.3
we get, 7.5 = 8.3 + log [A]/[HA]
log [A]/[HA] = -0.8 ==> [A]/[HA] = 0.16
since, [A]+[HA] = 0.1 M
thus, [HA] = 0.086M and [A] = 0.014 M
===>
for 50 mL of buffer ,
we need , TRIS = 0.1 mol/L * 0.05 L = 0.005 moles
molar mass tris :121.1 g/mol
thus, mass TRIS = 0.6055 g
Amount of 1M HCl need to be added : ( from HA)
= 0.086* 50 mL / 1.0 M = 4.3 mL
==> add water to make volume 50 mL.