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TiliK225 [7]
3 years ago
11

The forensic technician at a crime scene has just prepared a luminol stock solution by adding 15.0 g of luminol into a total vol

ume of 75.0 mL of H2O. What is the molarity of the stock solution of luminol? Express your answer with the appropriate units.

Chemistry
1 answer:
Svet_ta [14]3 years ago
7 0

The answer is in the photo

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write both he full balanced ionic equation for the following reaction and the balanced net ionic equation. What are the specter
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A weight loss supplement is advertised in several popular beauty and fashion magazines. The advertisements claim that "the suppl
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A sample that weighs 103.75 g is a mixture of 30% helium atoms and 70% krypton atoms. How many particles are present in the samp
aalyn [17]
1) we calculate the molar mass of He (helium) and Kr (Krypton).
atomic mass (He)=4 u
atomic mas (Kr)=83.8 u

Therefore the molar mass will be:
molar mass(He)=4 g/mol
molar mass(Kr)=83.8 g/mol.

1) We can find  the next equation:
mass=molar mass  x number of moles.

x=number of moles of helium
y=number of moles of helium. 

(4 g/mol) x  +(83.8 g/mol)y=103.75 g
Therefore, we have the next equation:

(1)

4x+83.8y=103.75


2) We can find other equation:

We have 30% helium atoms and 70% Kryptum atoms, therefore we have 30% Helium moles and 70% of Krypton moles.

1 mol  is always 6.022 * 10²³ atoms or molecules, (in this case atoms).

Then:
x=number of moles of helium
y=number of moles of helium.
(x+y)=number of moles of our sample.

x=30% of (x+y)

Therefore, we have this other equation:
(2)

x=0.3(x+y)


With the equations(1) and (2), we have the next system of equations:

4x+83.8y=103.75

x=0.3(x+y)  ⇒ x=0.3x+0.3y  ⇒    x-0.3x=0.3y  ⇒ 0.7 x=0.3y ⇒ x=0.3y/0.7
⇒x=3y/7

We solve this system of equations by substitution method.
x=3y/7

4(3y/7)+83.8y=103.75
lower common multiple)7
12y+586.6y=726.25
598.6y=726.25
y=1.21

x=3y/7=3(1.21)/7=0.52

We have 0.52 moles of  helium and 1.21 moles of Krypton.

1 mol=6.022 * 10²³ atoms

Total number of particles=(6.022 *10²³ atoms /1 mol) (number of moles of He+ number of moles of Kr).

Total number of particles=6.022 * 10²³ (0.52+1.21)=6.022 * 10²³ (1.73)=
=1.044 * 10²⁴ atoms.

Answer: The sample have 1.044 * 10²⁴ atoms.
6 0
4 years ago
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