Question

How much of a 25mg/ml chloramphenicol stock solution do we need to make 400ml of growth media that has final 25ug/ml concentration of chloramphenicol?

Answer 1

Answer : The volume of chloramphenicol stock solution needed is, 0.4 mL

Explanation :

First we have to calculate the mass of chloramphenicol.

As, the mass of chloramphenicol in 1 mL of solution = $25\mu g=25\times 10^{-6}g$

So, the mass of chloramphenicol in 400 mL of solution = $\frac{400mL}{1mL}\times 25\times 10^{-6}g=0.01g$

Thus, the mass of chloramphenicol is, 0.01 g

Now we have to calculate the volume of chloramphenicol stock solution needed.

Concentration of chloramphenicol = $25mg/mL=25\times 10^{-3}g/mL$

As, $25\times 10^{-3}g$ of chloramphenicol needed 1 mL volume of chloramphenicol stock solution

So, $0.01g$ of chloramphenicol needed $\frac{0.01g}{25\times 10^{-3}g}\times 1mL=0.4mL$ volume of chloramphenicol stock solution

Thus, the volume of chloramphenicol stock solution needed is, 0.4 mL