Question

The chemical 5-amino-2,3-dihydro-1,4-phthalazinedione, better known as luminol, is used by forensic scientists in analyzing crime scenes for the presence of washed-away blood. Luminol is so sensitive that it can detect blood that has been diluted 10,000 times. A basic solution of luminol is often sprayed onto surfaces that are suspected of containing minute amounts of blood. Luminol has a molecular weight of 177 g/mol.Before investigating the scene, the technician must dilute the luminol solution to a concentration of 2.00×10−2 M . The diluted solution is then placed in a spray bottle for application on the desired surfaces. How many moles of luminol are present in 2.00 L of the diluted spray? Express your answer with the appropriate units.

Answer 1

Molecular weight of Luminol is m =177

mass of Luminol added m' = 20.0 g

Volume of water V = 75 mL = 0.075 L

We know that Molarity M = ( mass / Molar mass ) / Volumeof the solution in L

                                         = ( 20 / 177 ) / 0.075

                                         = 1.5065 M

So molarity of the stock solution M = 1.5065 M

(2) Molarity of the solution M = 0.03 M

Volume of the solution V = 2 L

No . of moles n = Molarity * Volume

                         = 0.03 M * 2 L

                         = 0.06 moles