posted by .

IN the polystyrene beaker, mix 20mL of 0.1 M Acetic acid and 25mL of 0.1M Sodium Acetate and immediately measure the pH. Remove the electrode and add 5ml of 0.1 M HCl to this buffer. Stir the solution and measure the pH.



concentration of acetic acid= 0.1M- 20ml
concentration sodium acetate= 0.1M- 25ml
concentration of hydrochloric acid- 0.1M - 5ml

pH measured:

Buffer solution- 4.69
Buffer + 5ml 0.1M HCL- 4.43

pH calculated????????????
Buffer solution- ?????
Buffer + 5ml 0.1M HCL- ?????


1.So i have to calculate pH before the addition of HCL

2. show CALCULATIONS for calculated pH after addition of HCl

I think i use the henderson hasselbalch equation:

pH= pka+log [A-]/[HA]
pH= pka+log [0.1][0.1]

I dunt know if i plugged in the right stuff and how do i calculate pka?????

  • Chemistry -

    yes and no.
    pH = pKa + log (base/acid)
    You are right that base is acetate and acid is acetic acid.
    You know pH = -log (H^+)
    pKa is done the same way.
    pKa = -log Ka. If you use 1.8 x 10^-5 for Ka of acetic acid, pKa = 4.74.

    Let's call acetic acid HAc, sodium acetate is NaAc and acetate ion is Ac^-.
    (HAc) = 0.1 M x (20 mL/45 mL) = ?? in the original solution.
    (Ac^-) = 0.1 M x (25 mL/45 mL) = ?? in the original solution.

    When adding HCl, the Ac^- ties it up as HAc (which ionizes only partially and that's why this is a good buffer--it won't let the HCl loose to ionize completely) so HAc increases by the amount of HCl added and the Ac^- decreases by the amount of HCl added. My advice is to work in moles or millimoles instead of concn It makes it simpler.

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions


    (1) A beaker with 165 mL of an acetic acid buffer with a pH of 5.00 is sitting on a bench top. The total molarity of the acid and conjugate base in the buffer is 0.100M. A student adds 7.20mL of a 0.320M HCl solution to the beaker. …
  2. Chemistry

    I did an experiment on Buffers: In a polystyrene beaker, mix 20 ml of 0.1M Acetic acid ad 25 ml of 0.1 M sodium acetate and immediately measure the pH. Remove the electrode and add 5 ml of 0.1 M HCL to this buffer. Stir the solution …
  3. Chemistry

    I actually posted this up before and Gk helped out but i don't understand the steps what do i enter for the pka for the first one?
  4. Chemistry

    I have a question about buffers. Part A So it starts with 20ml 0.1 sodium acetate and 25ml 0.1 acetic acid. Calculate ph of buffer is 4.74 because the acid and conjugate base have the same molarity correct?
  5. College Chemistry

    A buffer solution contains 0.120M acetic acid and 0.150M sodium acetate. a. How many moles of acetic acid and sodium acetate are present in 50.0 ml of solution?
  6. school

    What is the pH of 0.1 M formic acid solution?
  7. Chemistry

    You are preparing 500 mL of a 0.300 M acetate buffer at pH 4.60 using only sodium acetate, 3.00 M HCl, 3.00 M NaOH, and water. Calculate the quantities needed for each of the following steps in the buffer preparation. 1. Add sodium …
  8. chemistry

    If you add 5.0 mL of 0.50 M HCl solution to 20.0 mL to Buffer C, what is the pH of the buffer?
  9. chemistry

    How much of each solution will you need to mix to obtain 100 – 120 ml of 20 mM buffer pH 4.0?
  10. Buffer

    Show how would you prepare a solution of 500 mL of a 0.15 M acetate buffer, pH 4.6 based on one of the three methods illustrated in class and in the supplementary readings. You have available the following: 6 M HCl, 4 M acetic acid, …

More Similar Questions