Question

a solution of a metal ion has a molar absorptivity (E) of 75M^-1 at 450 nm. a 10mL sample of this solution was withdrawn and diluted to 250mL. from this diluted solution, a 5 mL sample was withdrawn and diluted to 100 mL. the absorbance of the final solution was .234. find the molarity of metal ion in the original solution.

Answer 1

You don't give the thickness of the sample for the final absorbance so I will assume it is the same (say 1 cm) as when the standards were made. So
A = ec*1
0.234 = 75 c
c = 0.234/75 = estimated 0.003 M but that was the final solution. The original M must be
approx 0.003 x (100/5) x (250/10) = ? M for the initial solution.