chemistry

This question I really don't get it. I tried tried tried to figure out how to start solve the problem but still couldn't figure out. So can you help me with one question PLEASE? If so, can you please explain to me how you get the answer? Also can you show me step by step of solving the problem? I need to know how to do this problem, I will have test on Monday so I need to understand it. Thank!

Here the question:

what is the pH of a solution that is 0.30 M in aniniline, C6H5NH2 and 0.15M in anilinium chloride, C6H5NH3Cl? Show the equation for ionziation

asked by Laura
  1. Have you had a class on the Henderson-Hasselbalch equation?
    pH = pKa + log[(base)/(acid)]
    The base is aniline (0.30M) and the acid is the chloride(0.15M). The pKa is the pKa of aniline. In my book the Kb for aniline is 3.94E-10 which makes pKb = 9.40 and that subtracted from 14 makes pKa = 4.60.
    The ionization equation for aniline is
    C6H5NH2 + HOH ==> C6H5NH3^+ + OH^-

    posted by DrBob222
  2. No, my professor didn't teach student on Henderson-Hasselbalch equation. My professor only show us the Henderson-Hasselblach forumla but not show how to use it. Also she didn't give us what is pKa for this problem. Anyway, thank you so much for your help.

    posted by Laura
  3. How did you get the 3.94E-10?

    posted by Laura
  4. As I stated in my response I looked up Kb for aniline in one of my texts and obtained 3.94E-10. You should look it up in your text; your text may have a slightly different value. However, -log Kb = pKb; therefore, pKb for aniline from my value is 9.40 and since pKa + pKb = 14, then pKa = 14-9.40 = 4.60.
    Then substitute into the HH equation this way,
    pH = 4.60 + log(0.30)/(0.15) and solve for pH. I get 4.90.

    There is another way to do it and not use the HH equation.
    ....C6H5NH2 + HOH ==> C6H5NH3^+ + OH^-
    I.....0.30.............0...........0
    C......-x...............x..........x
    E.....0.30-x.............x.........x

    Then Kb = (C6H5NH3^+)(OH^-)/(6H5NH2)

    ....C6H5NH3Cl^- ==> C6H5NH3^+ + Cl^-
    I....0.15..........0..........0
    C...-0.15..........0.15.......0.15
    E......0..........0.15.........0.15

    Now substitute into the Kb equation this way:
    (C6H5NH3^+) = x + 0.15 (x from the ionization of C6H5NH2 and 0.15 from the anilinium chloride.
    (OH^-) = x
    (C6H5NH2) = (0.30-x) and it look this way.

    3.94E-10 = (x+0.15)(x)/(0.30-x)
    Assume x+0.15 = 0.15 and assume 0.30-x = 0.30. You can do that since x is small. That gives you
    3.94E-10 = (0.15)(x)/(0.30) and solve for x which is OH^-.
    I get 7.88E-10 for OH and pOH = 9.10 and pH = 14-9.10 = 4.90.
    You can see why we use the Henderson-Hasselbalch equation; it is so much easier to use for buffer problems.

    posted by DrBob222
  5. Yea, I realized that HH is more easy and faster. I'm going use HH better instead other way. Anyway thank you so much for explain.

    posted by Laura

Respond to this Question

First Name

Your Answer

Similar Questions

  1. calculus

    this question is a multiple choice question, however i don't know how to start or finish it. The solution set of |3x+2|<1 contains... i need help trying to figure out how to solve for x. other then that i believe i could answer
  2. Maths Question

    the slope of a curve y=f(x) is given by dy/dx= (x-1)(x-2)^2(x-3)^3(x-4)^4(x-5)^5 for what value or values of x does y have a local maximum/miniumum? justify your answer. i tried solving this question but couldn't figure out how to
  3. 7th grade math

    The hypotenuse of a right triangle is 10 centimeters and one of the legs is 6 centimeters. the leg to the very left is 6 cm and the leg to the top is 10 cm. the bottom leg has a x for unknown. My teacher gave me the answer since I
  4. math

    Okay. so say their is a list of numbers: x y 0 3 1 5 2 7 3 9 4 11 I know how to answer a question like "use an equation to figure out Y when X is..." but how do you figure do " figure out X when Y is" ? I konw that the formula is
  5. math

    The math problem we need help with is: lbs of can collected by 4 children were as follows: #1 49 #2 72 #3 108 #4 121. the answer is 10. what is the question. where do i start to figure out what the question is their looking for?
  6. English

    we learned about objective and subjective opinions authors may have today and although I got every other question, I can't seem to figure out the following two: tell the objective and subjective opinion in each statement and list
  7. Math

    i have a question regarding statistics. i just don't know how to do it and would really appreciate if someone could tell how i can solve it. the question is; a) compute the mean and the standard deviation of the population? ive
  8. Chemistry

    Determine the unknown quantity in the following cell at 298.15 K. Pt(s) | H2(g, 1.0 bar)| H+(pH = ?) || Cl -(aq, 1.0 mol┬ĚL-1) |AgCl(s), Ag(s), ΔE = +0.36 V. (DrBob) I still wasn't able to figure out the other one--I posted
  9. Science

    I'm struggling to figure out velocity and understanding the formulas. My question I have to try and figure out is... If a block of wood dropped from a tall building has reached a velocity of 78.4 m/s, how long has it been falling?
  10. English: Ms. Sue

    Ms. Sue you've helped out in the past haha maybe you can help me again :D we learned about objective and subjective opinions authors may have today and although I got every other question, I can't seem to figure out the following

More Similar Questions