biochem

posted by .

I need to create a 100ml buffer with a pH of 4.00 using 0.100M Benzoic acid (pKa = 4.20)and 0.180M sodium benzoate. What volume of each material do I need to make this buffer? I think I need to use pH=pKa + log(A/HA)but am not sure if that is correct. Any help would be appreciated.

  • biochem -

    Yes, the Henderson-Hasselbalch equation is what you use.
    If x = mL sodium benzoate (base)
    then 100-x = mL benzoic acid(acid).

    4.00 = 4.20 + log(0.18x)/[(100-x)*0.1]
    and solve for x

  • biochem -

    I think that is where I keep getting stuck, with the basic math. I have 0.631 = .180x/10-0.1x and don't know where to go from there. Math was a long time ago for me :)

  • biochem -

    0.631 = (0.180x)/[(100-x)*0.100]
    0.631*[(100-x)*.100] = 0.180x
    multiply 0.631*0.100 first to obtain 0.0631, then
    0.0631*(100-x) = 0.180x
    6.31-0.0631x = 0.180x
    6.31 = 0.0631+0.180x
    6.31 = 0.2431x
    x = 6.31/0.2431 = 25.96 mL
    100-x = 74.04 mL
    These should be rounded to 26.0 mL and 74.0 mL.
    You should check this by multiplying 26.0x0.180 = ?? and 74.0 x 0.100 mL = ??, substitute into the HH equation and see if you arrive at a pH of 4.00.

  • biochem -

    thank you so much. I just recently went back to school and havent had chemistry in more than 4 years and math has been even longer. I really appreciate the help :)

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. Chemistry

    Given that the Ka of benzoic acid is 6.50 x 10-5, how would one prepare 0.500 L of a benzoic acid/sodium benzoate buffer of a desired pH of 4.00?
  2. Chemistry

    Given that the Ka of benzoic acid is 6.50 x 10-5, how would one prepare 0.500 L of a benzoic acid/sodium benzoate buffer of a desired pH of 4.00?
  3. Chemistry

    You need to prepare 100.0 mL of a pH=4.00 buffer solution using 0.100 M benzoic acid (pKa = 4.20) and 0.240 M sodium benzoate. How much of each solution should be mixed to prepare this buffer?
  4. Chemistry

    You are asked to prepare a pH=4.00 buffer starting from 1.50 L of 0.0200 \; M solution of benzoic acid C_6 H_5COOH and an excess of sodium benzoate C_ H_5 COONa. How many grams of sodium benzoate should be added to prepare the buffer?
  5. Chemistry

    You need to prepare 100.0 mL of a pH=4.00 buffer solution using 0.100 M benzoic acid (pKa = 4.20) and 0.180 M sodium benzoate How much of each solution should be mixed to prepare this buffer?
  6. chemistry

    URGENT!!! How many grams of sodium benzoate (NaC6H5CO2) must be added to 500 mL of 0.15 M benzoic acid (HC6H5CO2) to make a buffer solution with pH of 5.0?
  7. Chemistry

    You need to prepare 100.0 mL of a pH=4.00 buffer solution using 0.100 M benzoic acid (pKa = 4.20) and 0.220 M sodium benzoate. How much of each solution should be mixed to prepare this buffer?
  8. chemistry

    A buffer with a pH of 4.30 contains 0.25 M of sodium benzoate and 0.20 M of benzoic acid. What is the concentration of [H ] in the solution after the addition of 0.052 mol of HCl to a final volume of 1.5 L?
  9. chemistry buffer

    Calculate the amount of sodium acetate to be added to 100ml of a 0.100M acetic acid (pka=4.76) solution to obtain a buffer of pH 4.50.
  10. chemistry

    To create a 0.1 M carbonate buffer pH = 10.2. You choose to use a combination of HCO3- / CO32-. This buffer system has pKa = 9.9.   a) Calculate how much you need to weigh in each of the sodium salts, NaHCO3 and Na2CO3, to create …

More Similar Questions