Question

Part A The forensic technician at a crime scene has just prepared a luminol stock solution by adding 19.0 g of 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 = 1.43 M

Part B Before investigating the scene, the technician must dilute the luminol solution to a concentration of 6.00×10?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? Express your answer with the appropriate units. moles of luminol = 0.120 mol 

Part C What volume of the stock solution (Part A) would contain the number of moles present in the diluted solution (Part B)? Express your answer with the appropriate units.

Answer 1

Part A:

Number of moles = amount in g / molar mass

= 19.0 g/ 177 g/ mole

= 0.107 moles

Molarity = number of moles / volume in L

= 0.107 /0.075= 1.43 M

Part B

Molarity = number of moles / volume in L

6.00×10?2 M= number of moles / 2.0 L

number of moles= 0.12 Moles

part C:

Number of moles = 0.12 moles molarity = 1.43 M

Molarity = number of moles / volume inL

Volume in L= Number of moles / molarity

= 0.12/1.43

= 0.0839 L

= 83.9 ml