The chemical 5-amino-2,3-dihydro-1,4-phthalazinedione, better known as luminol,

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.

a.) The forensic technician at a crime scene has just prepared a luminol stock solution by adding 13.0 g of luminol to H2O creating a solution with a total volume of 75.0 mL.What is the molarity of the stock solution of luminol?

b.)Before investigating the scene, the technician must dilute the luminol solution to a concentration of 6.00×102 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?

Explanation / Answer

a) Molarity = mass of solute / molecular weight of solute x volume of solution in L

Volume = 75 mL = 75 / 1000 L

Masss=13 g

Mol wt = 177

moalrity = 13 X 1000 / 177 X 75 = 0.979 molar

b) the new concentration = 6.00×102 M

We know that

Molarity = number of moles of solute / Litre of solution

0.06 molar = moles / volume of solution = moles / 2L

so number of moles = 0.06 X 2 = 0.12 moles

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