Question

Part A) The forensic technician at a crime scene has just prepared a luminol stock solution by adding 15.0 g of luminol into a total volume of 75.0 mL of H2O. What is the molarity of the stock solution of luminol?

Part B) Before investigating the scene, the technician must dilute the luminol solution to a concentration of 5.00×10⁻² 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?

Answer 1

1)

Molar mass of C8H7N3O2,

MM = 8*MM(C) + 7*MM(H) + 3*MM(N) + 2*MM(O)

= 8*12.01 + 7*1.008 + 3*14.01 + 2*16.0

= 177.166 g/mol

mass(C8H7N3O2)= 15.0 g

use:

number of mol of C8H7N3O2,

n = mass of C8H7N3O2/molar mass of C8H7N3O2

=(15 g)/(1.772*10^2 g/mol)

= 8.467*10^-2 mol

volume , V = 75 mL

= 7.5*10^-2 L

use:

Molarity,

M = number of mol / volume in L

= 8.467*10^-2/7.5*10^-2

= 1.129 M

Answer: 1.13 M

2)

volume , V = 2.00 L

use:

number of mol,

n = Molarity * Volume

= 5.00*10^-2*2.00

= 0.100 mol

Answer: 0.100 mol