Question

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.

Answer 1

1. The molarity of the stock solution of luminol = 1,431 M

2. 0.12 moles of luminol is present in 2.00 L of the diluted spray

3. The volume of the stock solution (Part A) would contain the number of moles present in the diluted solution (Part B): 83.86 ml

Further explanation

Stoichiometry in Chemistry studies about chemical reactions mainly emphasizing quantitative, such as the calculation of volume, mass, amount, which is related to the number of ions, molecules, elements, etc.

In stoichiometry included :

• 1. Relative atomic mass
• 2. Relative molecular mass

is the relative atomic mass of the molecule

• 3. mole

1 mole is the number of particles contained in a substance with the same number of atoms in 12 gr C-12

1 mole = 6.02.10²³ particles

While the number of moles can also be obtained by dividing the mass (in grams) by the relative mass of the element or the relative mass of the molecule

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

Luminol (C₈H₇N₃O₂) is a substance used to detect traces of blood in the scene of a crime because it reacts with iron in the blood

a. a luminol stock solution by adding 19.0g of luminol into a total volume of 75.0mL of H2O.

So the molarity is

• 1. Luminol mole

- 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

so the mole:

mol = gram / relative molecular mass

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

mole = 0.1073

2. Molarity (M)

M = mole / volume

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

M = 1,431

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

mole = M x volume

mole = 6.10⁻² x 2

mole = 0.12

• c. Molarity of the stock solution (Part A) = 1,431 M

the number of moles present in the diluted solution (Part B) = 0.12

So the volume of the stock solution (Part A) would contain the number of moles present in the diluted solution (Part B) is:

volume = mol / M

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

volume = 0.08386 L = 83.86 ml

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

Answer 2

Answer:

I didn't solve part a) because you said in the statement that you needed only the answer from part c), therefore the answer equals:

n = 0.120 moles

V = 83.9 mL

Explanation:

The dilution of a 1.43 M to 0.06 M solution is 22.8 to 1 relative. Therefore, 22.8 parts of water must be added to the original solution. The amount of moles is calculated as follows:

n = M * V = 2 L * 0.06 M = 0.120 moles

The volume is calculated as follows:

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