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
astra-53 [7]
3 years ago
13

Calculate the pH for each of the cases in the titration of 25.0 mL of 0.180 M pyridine, C 5 H 5 N ( aq ) with 0.180 M HBr ( aq )

. A. before addition of any HBr B. after addition of 12.5 mL of HBr C. after addition of 24.0 mL of HBr D. after addition of 25.0 mL of HBr E. after addition of 34.0 mL of HBr
Chemistry
2 answers:
Oxana [17]3 years ago
4 0

Answer:

Explanations

Calculate the pH for each of the following cases in thetitration of 25.0 mL of 0.100 M pyridine, C5H5N(aq) with 0.100 MHBr(aq):

a.Before and addition of HBr

b.After addition of 12.5ml HBr

c.After addition of 15ml HBr

d.After addition of 25ml HBr

e.After addition of 33ml HBr

SOLUTION ;;;

Kb of pyridine =1.5*10^-9

a)let the dissociation be x.so,

kb=x^2/(0.1-x)

or 1.5*10^-9=x^2/(0.1-x)

or x=1.225*10^-5

so,

[OH-]=1.225*10^-5

so,

pOH=-log([OH-])

so pH=9.088

b)now this will effectively behave as a buffer

pKb=8.82

so pOH=pKb+log(salt/acid)

=8.82+log((12.5*0.1)/(25*0.1-12.5*0.1))

=8.82

so pH=14-pOH

=5.18

c)again using the same equation as the above,

pOH=pKb+log(salt/acid)

=8.82+log((15*0.1)/(25*0.1-15*0.1))

=9

so pH=14-9

=5

d)now the base is completely neutralised.so,

concentration of the salt formed=0.1/2

=0.05 M

so,

pH=7-0.5pKb-0.5log(C)

=7-0.5*8.82-0.5*log(0.05)

=3.24

e)concentration of H+=(33*0.1-25*0.1)/(33+25)

=0.01379

so pH=-log(0.01379)

=1.86

LuckyWell [14K]3 years ago
3 0

Answer:

Check Explanation.

Explanation:

(A). Before the addition of any acid at all, meaning that we only have a base. Therefore,

The concentration of the [OH^-] = √(kb × [pyridine].

The concentration of the [OH^-] = [√(1.7 x 10^-9 × 0.180M).

[OH^-] = 1.75 × 10^-5.

Recall that the formula for Calculating pOH is given below;

pOH= - log [OH-].

pOH = - log (1.75 x 10^-5).

pOH = 4.76.

Hence;

pH = 14.0 - pOH .

pH= 14.0 - 4.76.

pH = 9.24.

(B). After the addition of 12.5 mL of HBr. And this means that we should Calculate the pH at midpoint of the titration.

To solve this part we will first find the ka of the buffer acid and then using the value of the ka to find its pka.

(Recall; kb = 1.7 x 10^-9).

==> ka = 1 x 10^-14 / 1.7 x 10^-9.

ka= 5.9 x 10^-6.

==> pKa = - log Ka.

pKa= - log (5.9 x 10^-6).

pKa = 5.23.

So, back to the solution;

pH = pKa + log ([C5H5N] / [C5H5NH+]).

pH= 5.23 + log [0.180]/ [0.180].

pH = 5.23 + log 1.

pH = 5.23.

(C). Then, after addition of 24.0 mL of HBr. Therefore, we have used 24mL out of 25mL and it now remain 1mL.

pH = 5.23 + log (1.0 / 24.0 ).

pH= 5.23 - 1.4.

pH = 3.83.

(D). after addition of 25.0 mL of HBr.

( Recall ka = 5.9 x 10^-6).

So, we will first Calculate the number of moles of C5H5N.

C5H5N = 0.180 × 25.0.

C5H5N = 4.5 mmoles

Therefore, in this stage we are now having 4.5 mmoles of C5H5NH+ specie.

Hence, [C5H5NH+] = 4.5 / 50.0 mL = 0.09M.

Next, we Calculate [H3O+] from;

[H3O+] = √(0.09 × 5.9 x 10^-6).

[H3O+] = 5.31 × 10^-7.

Therefore,

pH = -log [H3O+] .

pH = - log (5.31 x 10^-7).

pH = 6.3.

(E). Then, after addition of 34.0 mL of HBr.

First, we Calculate the number of mmoles of HBr;

0.180 × 34 = 6.12.

Therefore, the excess mmoles= 6.12 - 4.5 = 1.62.

Since, we now have an extra 9mL, then, the concentration of the acid=

1.62 / 59mL.

= 0.027 M.

Then, pH= -log [0.027].

pH= 1.046.

You might be interested in
Can a bad thermostat cause radiator to blow
erastova [34]
I don't exactly know but probably so.
3 0
3 years ago
How is the information about cats found in myths and fairy tales and legends different from information gathered through science
forsale [732]
Scirnce uses a method of testing to declare rules or facts. myth and fairy tales have no way of being tested. cats are a physical creature we can see, test, and observe. a mythical idea canny be tested. for example: mermaids cannot be tested as we have none to observe.
5 0
3 years ago
How does repeatability have an effect on scientific research?
Bas_tet [7]
In science it is best to continue research, and rinse and repeat. This allows for a stronger hypothesis if you're results are the same every time, or change your hypothesis if you stumble upon new results. <span />
5 0
3 years ago
Number of moles in 31.99g O2 <br> And 176.8g NaCl
sergey [27]

#O_2

\\ \sf\longmapsto No\:of\;moles=\dfrac{Given\:mass}{Molar\:mass}

\\ \sf\longmapsto No\:of\:moles=\dfrac{31.99}{32}

\\ \sf\longmapsto No\:of\:moles\approx 1

#NaCl

\\ \sf\longmapsto No\:of\:moles=\dfrac{176.8}{58.5}

\\ \sf\longmapsto No\;of\:moles=3mol

8 0
2 years ago
Using the perodic table determine the number of protons for the element Li​
wolverine [178]
Answer is 3

because on the periodic table, the small number above every element is the number of protons
8 0
3 years ago
Other questions:
  • A 50 L cylinder is filled with argon gas to a pressure of 10130.0 kPa at 300°C. How many moles of argon gas does the cylinder co
    8·2 answers
  • How many moles of trifluoromethanoic acid (CHF3O3S) are present in 9.0345 × 1024 molecules of (CHF3O3S)?
    11·1 answer
  • Which of these examples is a water-conservation technique that also reduces water pollution
    11·2 answers
  • All of these are examples of things that produce light energy except.
    13·2 answers
  • The original list from the Stockholm Convention on Persistent Organic Pollutants (POPs) of 12 hazardous chemicals, called the __
    12·1 answer
  • QUESTION 20
    15·1 answer
  • Plz help with this digestive system
    9·2 answers
  • Determine the number of atoms in 73.0 grams of calcium, Ca. (The
    15·1 answer
  • One of the advantages of nylon over rayon is that nylon:
    12·1 answer
  • Use Boyle's Law to interpret the following problem and then select the correct answer below.
    15·1 answer
Add answer
Login
Not registered? Fast signup
Signup
Login Signup
Ask question!