Question

3) Starting with two stock buffer solutions (A and B) listed below, describe how you would mix them together to obtain the solutions i and ii. Write your answers to 3 significant figures.

i) 400 mL of 0.35 M NaCl, 10 mM Tris buffer (pH 8.0)

ii) 600 mL of 0.9 M NaCl, 10 mM Tris buffer (pH 8.0)

Stock buffer A: 3 M NaCl, 10 mM Tris buffer (pH 8.0)

Stock buffer B: 0.1 M NaCl, 10 mM Tris buffer (pH 8.0)

Answer 1

(i)

Assuming that we mix 'x' mL of buffer A and 'y' mL of buffer B.

We have the following equation for balancing the number of millimoles of NaCl:

3*x + y*0.1 = 400*0.35

We have the following equation for balancing the number of micromoles of Tris buffer:

10*x + y*10 = 400*10

Solving this we get:

x = 34.48 mL

y = 365.52 mL

(ii)

Assuming that we mix 'x' mL of buffer A and 'y' mL of buffer B.

We have the following equation for balancing the number of millimoles of NaCl:

3*x + y*0.1 = 600*0.9

We have the following equation for balancing the number of micromoles of Tris buffer:

10*x + y*10 = 600*10

Solving this we get:

x = 165.52 mL

y = 434.48 mL

Hope this helps !