1answer.
Ask question
Login Signup
Ask question
All categories
  • English
  • Mathematics
  • Social Studies
  • Business
  • History
  • Health
  • Geography
  • Biology
  • Physics
  • Chemistry
  • Computers and Technology
  • Arts
  • World Languages
  • Spanish
  • French
  • German
  • Advanced Placement (AP)
  • SAT
  • Medicine
  • Law
  • Engineering
S_A_V [24]
3 years ago
11

A chemist titrates 130.0mL of a 0.4248 M lidocaine (C14H21NONH) solution with 0.4429 M HBr solution at 25 degree C . Calculate t

he pH at equivalence. The pKb of lidocaine is 7.94 . Round your answer to 2 decimal places. Note for advanced students: you may assume the total volume of the solution equals the initial volume plus the volume of HBr solution added.
Chemistry
1 answer:
jeka57 [31]3 years ago
3 0

Answer:

pH = 3.36

Explanation:

Lidocaine is a weak base to be titrated with the strong acid HBr, therefore at equivalence point we wil have the protonated lidocaine weak conjugate acid of lidocaine which will drive the pH.

Thus to solve the question we will need to calculate the concentration of this weak acid at equivalence point.

Molarity = mol /V ∴ mol = V x M

mol lidocaine = (130 mL/1000 mL/L) x 0.4248 mol/L = 0.0552 mol

The volume of 0.4429 M HBr required to neutralize this 0.0552 mol is

0.0552 mol x  (1L / 0.4429mol) = 0.125 L

Total volume at equivalence is  initial volume lidocaine + volume HBr added

0 .130 L +0.125 L = 0.255L

and the concentration of protonated lidocaine at the end of the titration will be

0.0552 mol / 0.255 L = 0.22M

Now to calculate the pH we setup our customary ICE table for  weak acids for the equilibria:

protonated lidocaine + H₂O   ⇆  lidocaine + H₃O⁺

                      protonated lidocaine          lidocaine        H₃O⁺

Initial(M)               0.22                                       0                  0

Change                   -x                                      +x                 +x

Equilibrium          0.22 - x                                  x                    x

We know for this equilibrium

Ka = [Lidocaine] [H₃O⁺] / [protonaded Lidocaine] =  x² / ( 0.22 - x )

The Ka can be calculated from the given pKb for lidocaine

Kb = antilog( - 7.94 ) = 1.15 x 10⁻⁸

Ka = Kw / Kb = 10⁻¹⁴ / 1.15 x 10⁻⁸  = 8.71 x 10⁻⁷

Since Ka is very small we can make the approximation 0.22  - x  ≈ 0.22

and solve for x. The pH  will then  be the negative log of this value.

8.71 x 10⁻⁷  = x² / 0.22 ⇒ x = √(/ 8.71 X 10⁻⁷ x 0.22) = 4.38 x 10⁻⁴

( Indeed our approximation checks since 4.38 x 10⁻⁴ is just 0.2 % of 0.22 )

pH = - log ( 4.4x 10⁻⁴) = 3.36

You might be interested in
Most seeds germinate and start to grow in the dark. Why don’t they need light right away?
White raven [17]

Answer:

HD video is the best way too much for a TV now

8 0
3 years ago
Please help to me solve these ! :)
emmainna [20.7K]
I. The solubility of NaCl at 25 degrees C would be between the solubilities at 20 and 30 degrees C. A reasonable answer would be 36 grams/100 g water
ii. From the table, it’s clear that the salts are more soluble at higher temperatures, indicating that an increase in temperature increases solubility.
iii. At 50 degrees C, a saturated ammonium chloride solution will have 50.6 grams of salt per 100 g water. At 20 degrees C, the solution can hold only 37.3 grams of salt per 100 g water. Thus, 13.3 grams of salt will precipitate per 100 grams of water.
4 0
3 years ago
Read 2 more answers
As ice melts from a solid to a liquid, A) entropy increase
Dovator [93]
That answer is false 
4 0
3 years ago
What's is the mass of 0.500 mol NH3​
Setler [38]

Answer:

8.5155g NH3

Explanation:

the molar mass of NH3​ is 17.031 g/mol

0.5 mol NH3 x 17.031 gNH3/1 mol NH3 = 8.5155g NH3

4 0
3 years ago
The notation for the nuclide 13755Cs gives information about
k0ka [10]

Answer is (3) both mass number and atomic number.

The notation is ₅₅¹³⁷Cs. The Cs represents the chemical symbol of Caesium element. The subscript number at the left hand side of the symbol indicates the atomic number. Hence, atomic number of Cs is 55. The superscript number at the left hand side of the symbol shows the mass number. Hence, the mass number of the Cs is 137.

5 0
3 years ago
Other questions:
  • The legs and the wings of an insect are attached to the ________. a. head b. thorax c. abdomen d. antennae
    13·2 answers
  • Which of the following is a property of salts? (5 points)
    13·2 answers
  • HELP MEEEE ASAP PLEASEEEE !!!!!!!!
    8·1 answer
  • In two or more complete sentences describe all of the van der Waals forces that exist between molecules of sulfur
    14·2 answers
  • State briefly the similarities and differences between the theories of Arrhenius and Bronsted-Lowry
    14·1 answer
  • Why does increasing the temperature make a solid dissolve faster?
    11·1 answer
  • Make an oblique drawing (page 9)
    14·1 answer
  • In electromagnetic waves, the frequency and wavelength are inversely proportional, which means if one gets larger,
    14·2 answers
  • What factors have caused the rise in global temperatures over the past century?
    15·1 answer
  • A woman has a body mass of 53 kg. What is her mass in grams?
    6·2 answers
Add answer
Login
Not registered? Fast signup
Signup
Login Signup
Ask question!