Question

how would you prepare solutions of 100 ug/mL, 5ug/mL and 1 ug/mL concentrations starting with a solid? You have volumetric pipets: 1, 5, 10, 25, and 50 mL and volumetric flasks: 10, 25, 50, 100 and 250 mL.  

Answer 1

If you can weigh the solid 0.1 g and transfer into a 10 mL volumetric flask. Fill the flask to make 10 mL solution.
The concentration of this stock is

M1 = 0.1 g x 1/10 mL = 0.01 g/mL

From, this stock M1 we can use 1 mL and transfer into 100 mL volumetric flask. then, dilute the solution to 100 mL.

The resulted solution concentration is

M2 = M1 x V1/V2 = 0.01 g/mL x 1 mL /100 mL = 0.0001 g/mL = 100 ug/mL

Now, we can use M2 solution to make another concentration stock. Take 25 mL of M2 solution and tranfer into 250 mL
flask. Then fill the solution upto 250 mL . The resulted solution concentration will be

M3 = M2 x V2/V3 = 100 ug/mL x 25 mL / 250 mL = 10 ug/mL

We need to make 5 ug/mL and 1 ug/mL

So, we take 25 mL of M3 solution and transfer into 50 mL flask. Dilute the solution upto 50 mL. the resulting
solution concentration will be

M4 = M3 x V3 /V4 = 10 ug/mL x 25 mL / 50 mL = 5 ug/mL

Form the M4 we take 5 mL and transfer into 25 mL flask. Dilute the solution upto 25 mL . the resulting
solution concentration will be

M5 = M4 x V4 /V5 = 5 ug/mL x 5 mL / 25 mL = 1 ug/mL