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nika2105 [10]
3 years ago
11

The forensic technician at a crime scene has just prepared a luminol stock solution by adding 16.0 g of luminol into a total vol

ume of 75.0 mL of H2O. What is the molarity of the stock solution of luminol?
Chemistry
1 answer:
nikitadnepr [17]3 years ago
6 0

 The  molarity  of  the stock solution of  luminol  is 1.2 M


 <u><em>calculation</em></u>

step 1:  find the moles  of  luminol  using   (moles=  mass/molar mass)  formula


molar  mass  of Luminol= 177 g/mol

moles  is therefore= 16.0 g/ 177  g/mol=0.0904 moles


Step  2:  find the molarity  using (molarity= moles/volume in liters)  formula

     convert  Ml  into liters =  75.0/1000= 0.075 L

  molarity is therefore= 0.0904 moles/ 0.075 L= 1.2M

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Calculate the concentration of formate in a 100mm solution of formic acid at ph 4.15. The pka for formic acid is 3.75
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The molarity of formic acid is 100 mM or 100\times 10^{-3}M. The dissociation reaction of formic acid is as follows:

HCOOH\leftrightharpoons HCOO^{-}+H^{+}

The expression for dissociation constant of the reaction will be:

K_{a}=\frac{[HCOO^{-}][H^{+}]}{[HCOOH]}

Rearranging,

[HCOO^{-}]=\frac{K_{a}[HCOOH]}{[H^{+}]}

Here, pH of solution is 4.15 thus, concentration of hydrogen ion will be:

[H^{+}]=10^{-pH}=10^{-4.15}=7.08\times 10^{-5}M

Similarly, pK_{a}=3.75 thus,

[K_{a}=10^{-pK_{a}}=10^{-3.75}=1.78\times 10^{-4}M

Putting the values,

[HCOO^{-}]=\frac{(1.78\times 10^{-4}M)(100\times 10^{-3}M)}{(7.08\times 10^{-5}M}=0.2511 M

Therefore, the concentration of formate will be 0.2511 M.

4 0
3 years ago
Who first argued that all matter is made up of particles so small that they could not possibly be divided
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PLEASE HELP!!!! 20 MINS LEFT IM DYING PLS HELP
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Answer:

Kc = 0.20        

Explanation:

                  N₂O₄     ⇄    2NO₂

moles       5.3mol          2.3mol

Vol               5L                5L

Molarity    5.3/5M        2.3/5M

                = 1.06M     = 0.46M

Kc = [NO₂]²/[N₂O₄] =  (0.46)²/(1.06) = 0.1996 ≅ 0.20

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Answer:

Li2O+H2O---->(2)LiOH

Explanation:

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Potassium has a mass number of 40 and an atomic number of 19. how many protons does it have?
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