The forensic technician at a crime scene has just prepared a luminol stock solut

Question

The forensic technician at a crime scene has just prepared a luminol stock solution by adding 17.0 g of luminol a total volume of 75.0 mL of H_2 O. What is the molarity of the stock solution of luminol? Express your answer with the appropriate units. molarity of luminol solution = Before investigating the scene, the technician must dilute the luminol solution to a concentration of 4.00 times 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. moles of luminol =

Explanation / Answer

A)

m = 17 g of luminol

V = 75 mL of water

then

M = mol / V

mol = mass/MW =

MW luminol = 177.16 g/mol

so

mol = 17/177.16 = 0.0959584 mol

now

V= 75 mL = 0.075 L

M = 0.0959584/0.075

M = 1.2794 m of luminol

B)

for dilution

M2 = 4*10^-2 M

so

M1*¨V1 = M2*V2

1.2794*75 = 0.04*V2

V2 = 1.2794*75 /0.04

V2= 2398.875 mL =

calculate moles

mol = M*V = (2398.875*10^-3)(4*10^-2) = 0.095955 moles will be present

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