Question

A standard solution containing 6.6 10-8 M iodoacetone and 2.2 10-7 M p-dichlorobenzene (an internal standard) gave peak areas of 348 and 715, respectively, in a gas chromatogram. A 3.00 mL unknown solution of iodoacetone was treated with 0.100 mL of 1.2 10-5 M p-dichlorobenzene and the mixture was diluted to 10.00 mL. Gas chromatography gave peak areas of 419 and 479 for iodoacetone and p-dichlorobenzene, respectively. Find the concentration of iodoacetone in the 3.00 mL of original unknown.

Answer 1

2.2 x 10^-7 M p-dichlorobenzene standard in a standard solution gave a peak intensity 715

6.6 x 10^-8 M iodoacetone gave a peak intensity in standard solution = 348

0.1 ml of 1.2 x 10^-5 M p-dichlorobenzene in 3 ml unknown solution diluted to 10 ml

Final concentration of p-dichlorbenzene in dilute solution = 1.2 x 10^-5 x 0.1/10 = 1.2 x 10^-7 M

1.2 x 10^-7 M p-dichlorbenzene standard gave intensity of 479

concentration of iodoacetone in dilute solution = 419 x 6.6 x 10^-8/348 = 7.95 x 10^-8 M

So the concentration of iodoacetone in 3 ml original solution = 10 x 7.95 x 10^-8/3 = 2.65 x 10^-7 M