Question

± Molarity

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.

Part A

The forensic technician at a crime scene has just prepared a luminol stock solution by adding 10.0 gof luminol into a total volume of 75.0 mL of H2O.

What is the molarity of the stock solution of luminol?

Express your answer with the appropriate units.

molarity of luminol solution =

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Part B

Before investigating the scene, the technician must dilute the luminol solution to a concentration of 4.00×10⁻²M . 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 =

Answer 1

Part A

molar mass of luminol = 177gm/mol that mean 1 mole of luminol = 177gm then 10 gm of luminol = 10/177 = 0.056497 mole of luminol

10 gm of luminol = 0.056497 mole of luminol

75 ml = 0.075 L

molarity = no. of mole / volume of solution in liter

= 0.056497 / 0.075 = 0.753293 M

Molarity of luminol solution = 0.753293 M

Part B

No. of mole = molarity volume of sollution in liter

= 4.0010^-2   2 = 0.08 mole

moles of luminol = 0.08 mole.