Question

To prepare and analyse an unknown sample containing traces of lead using Atomic Adsorption Spectroscopy (AAS). An analytical chemist purchases a 250 mL lead standard for AAS; certified to contain Pb at a concentration of 1000 mg/l with an uncertainty of ±4 mg/L. To prepare the stock solution for the calibration, the analyst uses a micropipette with an uncertainty of ±0.8% to transfer 100.0 μL of the commercial standard to a Class-A 100 mL volumetric flask with an uncertainty of ±0.1 mL.

a) Using conventional rounding rules, calculate the concentration of Pb²⁺ the final solution.

Answer 1

Standard solution concentration of Pb 1000 mg/l i.e. 1000 ppm

To prepare stock solution –

From this 100 ul were added into volumetric flask and diluted upto 100mL

To calculate concentration of Pb2+ solution

C1 = Concentration of standard solution is 1000ppm

V1 = Volume of standard solution is 100 ul

C2 = concentration of stock solution (to calculate)

V2 = Volume of stock solution to prepare

C1V1 = C2V2

1000ppm*0.1mL = C2*100mL

C2 = 1000*0.1/100

C2 = 1ppm

Concentration of Pb2+ = 1ppm