Question

Describe how to prepare a 20.00 ug/ml iron solution from a 1,000 mg/ml iron standard solution using 10-ml and 50-ml volumetric pipets and 500-ml and 1,000-ml volumetric flasks.

Answer 1

We have been given 1000 mg/mL stock solution = 1000 10^-3 g/mL = 1 g/mL

And we need to prepare 20.00 g/mL = 20.00 10^-6 g/mL

C1V1 = C2V2................................where C1= stock solution concentration, C2=needed concentration, V1=needed volume of stock solution, V2=volume of final after dilution (consider 1000 mL)

Thus, (1 g/mL) (V1) = (20.00 10^-6 g/mL) (1000 mL)

V1 = (20.00 10^-6 g/mL) (1000 mL) / 1g/mL

V1 = 0.02 mL of stock solition.

However, we can not pipet out such small quantity using even smallest pipet. Hence we need to do the further dilution of stock solution. Consider we want to prepare 0.01 g/mL of 500 mL solution from given stock.

Thus, Volume of stock solution neede = (0.01 500) / 1 = 5mL

Now pipet out 5mL of stock solution into 500 mL volumetric flask and dilute it to the mark which gives us 0.01 g/mL solution.

Now take this solution for further dilution.

Now our values are, C1 = 0.01 g/mL, C2=(20.00 10^-6 g/mL), and (V2 = 1000 mL)
V1 = (20.00 10^-6 g/mL) (1000 mL) / 0.01
V1 = 2 mL

Thus we can pipet out 2mL of 0.01 g/mL solution in 1000 mL volumetric flask and dilute it to the mark to get 20.0020.00 g /mL solution.