The chemical5-amino-2,3-dihydro-1,4-phthalazinedione, better known as luminol,is

Question

The chemical5-amino-2,3-dihydro-1,4-phthalazinedione, better known as luminol,is used by forensic scientists in analyzing crime scenes for thepresence of washed-away blood. Luminol is so sensitive that it candetect blood that has been diluted 10,000 times. A basic solutionof luminol is often sprayed onto surfaces that are suspected ofcontaining minute amounts of blood.

Luminol has a molecular weight of 177g/mol.

The forensic technician at a crimescene has just prepared a luminol stock solution byadding 16.0 g of luminol into a total volume of 75.0 mlof H2O.

What is the molarity of the stocksolution of luminol?

Before investigating the scene, thetechnician must dilute the luminol solution to a concentrationof 4.00×102 M. The dilutedsolution is then placed in a spray bottle for application on thedesired surfaces.

How many moles of luminol are presentin 2.00 L of the diluted spray?

Explanation / Answer

Molarity , M = ( mass / Molar mass ) / Volime in L                     = ( 16 g / 177 g / mol ) / 0.075 L                     = 1.2053 moles / L So the molarity of the stock solution , M = 1.2053 M The concentration of luminol before investigation , M' = 4 *10^-2 M Volume of the solution , V = 2 L We know that Molarity , M = no . of moles / Volume of solutionin L                           So , no . of moles , n = M * V                                                           = 4* 10^-2 M * 2 L                                                           = 0.08 moles

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