chemistry

posted by .

What happens when 4ml of 1M HCL is added to 100ml buffer made using 5ml 1M Na2HPO4 and 5ml 1M NaH2PO4? The pKa for H+ + HPO4- = H2PO4 is 6.82.

  • chemistry -

    Use the Henderson-Hasselbalch equation.
    pH = pKa + log [(base)/(acid)]

    H^+ + HPO4^-2 ==> H2PO4^-
    You start with 0 millimoles H^+.
    You start with 5 x 1 = 5 millimoles HPO4^-2
    You start with 5 x 1 = 5 millimoles H2PO4^-1.

    Now you add 4 x 1 = 4 millimoles H^+.
    That reacts with 4 millimiles HPO4^-2 to form 4 millimoles H2PO4^- (plus the 5 already there = 9 millimoles H2PO4^-).

    That leaves 5 millimoles HPO4^-2 - 4 millimoles that reacted with H^+ = 1 millimole HPO4^-.
    Plug into HH equation and solve for pH.
    Check my work. It's easy to leave type a wrong charge, etc.

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. Chemistry

    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. _______________ …
  2. chemistry

    what is the pH of the buffer when 4ml of 1M HCl is added to a 100ml buffer solution made using 5ml 1M Na2HPO4 and 5ml 1M NaH2PO4?
  3. Chemistry

    Calculate the amount of NaH2PO4 and Na2HPO4 needed to prepare 100 mL of a buffer with a pH = 8.25 so that the sum of concentrations of HPO4 and H2PO4 ions is 0.5 M. Where do I start?
  4. chem: Drbob222

    Hi I have a follow up to a question that was answered previously. New question: So when the HPO4(2-) reacts with the NaOH, will the equation be this?
  5. Chemistry

    How do I calculate the amount of grams of Na2HPO4 and NaH2PO4 to prepare 200 mL of a buffer with an 8.25 pH so the sum of the concentrations of HPO4 and H2PO4 ions is 0.5 M?
  6. Chemistry

    How do I calculate the amount of grams of Na2HPO4 and NaH2PO4 to prepare 200 mL of a buffer with an 8.25 pH so the sum of the concentrations of HPO4 and H2PO4 ions is 0.5 M?
  7. Chemistry

    How would you calculate the pH of the buffer if 1.0mL of 5.0M NaOH is added to 20.0mL of this buffer?
  8. Chemistry

    How would you calculate the pH of the buffer if 1.0mL of 5.0M NaOH is added to 20.0mL of this buffer?
  9. Chemistry

    I have the answer to this question but the book does not explain WHY this is a good buffer solution?
  10. Chemistry

    Phosphate can act as buffer: H2PO4- HPO4^2- + H+ The pKa of this equilibrium is 7.21. What is the ratio of H2PO4- to HPO4^2- at pH 7.0?

More Similar Questions