Help on part "c": The forensic technician at a crime scene has just prepared a luminol stock solution by adding 19.0g of luminol

Question

3 months ago

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Help on part "c": The forensic technician at a crime scene has just prepared a luminol stock solution by adding 19.0g of luminol

into a total volume of 75.0mL of H2O.
a)What is the molarity of the stock solution of luminol?
anwer I got: molarity of luminol solution = 1.43M 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.
I cannot get the correct answer for "c"...I have tried: 172mL,11.9mL, and 1.19*10^4. The only other possibility that I can come up with is: 83.9mL. Would this one be correct?...Or...am I still completely out to lunch???
c)How many moles of luminol are present in 2.00 L of the diluted spray?
anwer I got: moles of luminol = 0.120mol What volume of the stock solution (Part A) would contain the number of moles present in the diluted solution (Part B)?
Express your answer in milliliters.

Chemistry

2 answers:

lions [2.9K] · Answer 1 · 2026-02-25T23:01:09+03:00

1. The luminol stock solution has a molarity of 1.431 M.

2. In 2.00 L of the diluted spray, there are 0.12 moles of luminol.

3. The volume of the stock solution from Part A that contains the same number of moles present in the diluted solution from Part B is 83.86 ml.

Additional Information

Stoichiometry in Chemistry focuses on the quantitative aspects of chemical reactions, which includes calculations related to volume, mass, and the count of ions, molecules, and elements.

Key concepts in stoichiometry include:

1. Relative atomic mass
2. Relative molecular mass

This refers to the relative atomic mass of a molecule.

3. Mole

A mole represents the number of particles in a substance equivalent to the number of atoms in 12 grams of carbon-12.

1 mole = 6.02 × 10²³ particles.

The quantity of moles can also be derived by dividing mass (in grams) by either the relative mass of an element or the relative mass of a molecule.

$\large{\boxed{\bold{mol\:=\:\frac{grams}{ relative\:mass} }}}$

Luminol (C₈H₇N₃O₂) is utilized for detecting blood traces at crime scenes, due to its reaction with iron found in blood.

To prepare a luminol stock solution, 19.0 g of luminol is mixed into a total volume of 75.0 mL of water.

Thus, the molarity is calculated as:

1. Moles of Luminol

- the relative molecular mass of Luminol:

= 8.C + 7.H + 3.N + 2.16

= 8.12 + 7.1 + 3.14 + 2.16

= 177 grams/mol.

Thus, we have:

moles = grams / relative molecular mass.

$mole=\frac{19}{177}$

moles = 0.1073.

2. Molarity (M)

M = moles / volume

$M\:=\:{\frac{ 0.1703 }{75.10^{-3} L}$

M = 1.431.

b. The concentration of luminol in the spray bottle is 6.00 × 10⁻² M. Therefore, in a 2 L solution, the number of moles is:

moles = M × volume

moles = 6 × 10⁻² × 2

moles = 0.12.

c. The molarity of the stock solution (Part A) is 1.431 M.

The diluted solution (Part B) contains 0.12 moles of luminol.

To find the volume of the stock solution (Part A) that has the same moles as the diluted solution (Part B):

volume = moles / M

$volume\:=\:\frac{0.12}{1.431}$

volume = 0.08386 L = 83.86 mL.

Further Learning

moles of water you can generate

the amount of each atom in the chemical's formula

the proportion of hydrogen to oxygen atoms in 2 L of water

Keywords: mole, volume, molarity, Luminol, relative molecular mass

eduard [2.7K] · Answer 2 · 2026-02-25T23:00:25+03:00

Response:

I didn't work on part a) since you mentioned that you only needed the answer for part c), therefore the result is:

n = 0.120 moles.

Volume = 83.9 mL.

Reasoning:

The dilution from a 1.43 M solution to a 0.06 M solution is in a ratio of 22.8 to 1. Thus, to the original solution, 22.8 parts of water should be added. The calculation of moles is done as:

n = M × V = 2 L × 0.06 M = 0.120 moles.

To find the volume, use this calculation:

V = n/M = 0.120 moles / 1.43 M = 83.9 mL.