A biologist needs 500 mL of a 10 mM phosphate buffer. The stock solution of the buffer is 100 mM. How much stock solution should be used to make the 10 mM phosphate buffer?
A) 500 mL
B) 5000 mL
C) 50 mL
D) 5.0 mL
E) 0.5 mL

Question

Quizplus · Accepted Answer

The concentration of the stock solution is 100 mM and the desired concentration is 10 mM.

We can use the formula:

C1V1 = C2V2

Where: 
C1 = concentration of stock solution
V1 = volume of stock solution needed
C2 = desired concentration
V2 = final volume

Plugging in the numbers,

100 mM x V1 = 10 mM x 500 mL

V1 = (10 mM x 500 mL)/100 mM = 50 mL

Therefore, 50 mL of the stock solution should be used to make 500 mL of the 10 mM phosphate buffer.

A Biologist Needs 500 ML of a 10 MM Phosphate