Chemistry

posted by .

In the study of biochemical processes, a common buffering agent is the weak base trishydroxymethylaminomethane, often abbreviated as Tris. At 25 C, Tris has a pKb of 5.91.
The hydrochloride can be abbreviated as Tris HCl.

What volume of 10.0 M NaOH is needed to prepare a buffer with a pH of 7.79 using 31.52 g of Tris HCl?

I found this answer to be 6.6755 mL


This is what I can't figure out:

The buffer from Part A is diluted to 1.00L . To half of it (500 mL ), you add 0.0250 mol of hydrogen ions without changing the volume. What is the pH of the final solution?

  • Chemistry -

    I don't believe your answer to the first part is correct.
    pKa = 14-pKb = 8.09
    7.79 = 8.09 + log[(base)/(acid)]
    B/A = 0.501 or
    base = 0.501*acid
    If acid is 31.52 g then we start with 31.52/157.6 (check my molar mass) = 0.2 mole acid; therefore,
    base = 0.2 mole x (0.501) = 0.1 mole for base.
    With 10 M NaOH, we have M = moles/L
    10M = 0.1/L or L = 0.1/10 = 0.01 L = 10 mL of the 10 M NaOH (and not the 6.6755 you calculated but check me out on that).

    For part B, I would do it this way.
    Diluting to 1.00 L and take 1/2 that means we have 0.05 moles acid and 0.05 mole base.
    ..........TRIS.HCl ==> B... +... H^+
    initial:...0.05 mole....0.05 mole....0
    add........0.............0......0.0250
    change......+0.025....-0.025....-0.0250
    final..... 0.075.......0.025.....0

    Then use the HH equation to calculate the final pH. I get
    pH = 8.09 + log(0.0250/0.0750) = 7.61
    Check my work carefully.

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. chemistry

    An enzyme-catalyzed reaction is carried out in a 50-mL solution containing 0.1 M TRIS buffer. The pH of the reaction mixture at the start was 8.0. As a result of the reaction, 0.002 mol of H+ were produced. What is the ratio of TRIS …
  2. chemistry lab

    An enzyme-catalyzed reaction is carried out in a 50-mL solution containing 0.1 M TRIS buffer. The pH of the reaction mixture at the start was 8.0. As a result of the reaction, 0.002 mol of H+ were produced. What is the ratio of TRIS …
  3. Biochem

    Calculate the amount of Tris(hydroxlmethyl)aminomethane(Tris) necessary to make 100mL of a 0.100 M Tris buffer that is equimolar in Tris-base (MW=121.1 g/mol) and Tris-HCL (MW= 157.6g/mol)
  4. chemistry

    Tris(hydroxymethyl)aminomethane, commonly called TRIS or Trizma, is often used as a buffer in biochemical studies. Its buffering range is pH 7 to 9, and Kb is 1.19 10-6 for the following aqueous reaction. (HOCH2)3CNH2 + H2O (HOCH2)3CNH3+ …
  5. Biochemistry

    How do you prepare 100 mL of a 0.1 M TRIS-HCl buffer with a pH 7.4 using solid TRIS base (MW 121.1) and 1 M hydrochloric acid?
  6. Chemsitry

    Tris is an abbreviation for tris (hydroxymethyl) aminomethane, which is a weak base. Calculate how many grams of tris (mw=121.14g/mol) are needed to make 25mL of 0.10M tris solution. Calculate how many mL of 0.25M HCl are needed to …
  7. chemistry

    Prepare 1.5 liters of 0.25 M Tris buffer, pH 7.5. Useful information: pKa Tris = 8.1 Formula weight of Tris (hydroxymethyl aminomethane) base = 121.1 Formula weight of Tris hydrochloride (acid form) = 158.0
  8. Chemistry

    Calculate the pH of a solution prepared by dissolving 10.0 g of tris(hydroxymethyl)aminomethane ("tris base") plus 10.0 g of tris hydrochloride in 0.250 L of water. (a) What will be the pH if 10.5 mL of 0.500 M NaOH is added?
  9. BCH

    How many gramms of Tris and Tris Hcl are needed to make up 500ml of 1m Tris with a PH of 8.0?
  10. biochemistry

    how many grams each of tris and tris HCl are needed to make up 500ml of 1m tris buffer with a PH of 8.0. pka of tris =8.3 mwt of tris =121 mwt of tris HCl =175

More Similar Questions