1. Questions

Chemistry

Calculate the pH for each of the following points in the titration of 50.0 mL of a 2.7 M H3PO3(aq) with 2.7 M KOH(aq).

pKa1 = 1.3 and pKa2 = 6.7

a) before addition of any KOH
b) after addition of 25.0 mL of KOH
c) after addition of 50.0 mL of KOH
d) after addition of 75.0 mL of KOH
e) after addition of 100.0 mL of KOH

  1. 👍 0
  2. 👎 0
  3. 👁 2,412
KB

  1. The problem is too long to work; however, if you will tell me what you know about it and what you don't understand about it I can help you through it.
    The process involves three stages.
    1. at the beginning, 0 mL KOH added.
    2. hydrolysis of the salts at each equivalence point.
    3. the pH of all points between equivalence point.
    4. After the last equivalence point.

    1. 👍 0
    2. 👎 0
    DrBob222

  2. I'm not sure how to set up the equations using the volumes, and I'm not even sure what givens I'm supposed to use.

    1. 👍 0
    2. 👎 0
    KB

  4. mols H3PO4 = M x L = 2.7 x 0.050 = 0.135.

    (1) NaOH + H3PO4 ==> NaH2PO4 + H2O
    (2) NaOH + NaH2PO4 ==> Na2HPO4 + H2O

    Where are the equivalence points for equn 1 and 2 above?
    So it will take 0.135 mol KOH for the first and another 0.135 for the second. Since the M of the KOH is the same as M H3PO4, this means mL will be the same. Therefore, the first equivalence point (the first H is titrated) with 50 mL KOH and the second with another 50 mL KOH. Look at the problem.
    a is at the beginning.
    c. is the first e.p.
    b. is halfway between beginning and e/p/
    e. is the 2nd e.p.
    e. halfway between 1st and 2nd e.p.

    a. at the beginning.
    ...........H3PO4 ==> H^+ + H2PO4^-
    I...........2.7M......0......0
    C...........-x.........x......x
    E..........2.7-x.......x.......x

    kl = (H^+)(H2PO4^-)/(H3PO4)
    Substitute and solve for x = (H^+) and convert to pH.

    For part c and e you have hydolysis of the salts. c is (H^+)= sqrt(k1k2)
    e is (H^+) = sqrt(k2k3)
    Parts b and d are solved using the Henderson-Hasselbalch equation.

    1. 👍 0
    2. 👎 0
    DrBob222

  5. Thanks!

    1. 👍 0
    2. 👎 0
    KB

Respond to this Question

First Name

Your Response

Similar Questions

  1. chemistry

    CH3NH2(aq)+H2O(l)=>CH3NH3+(aq)+OH-(aq) Kb=4.4 x 10^-4 Methylamine, CH3NH2, is a weak base that reacts with water according to the equation above. A student obtains a 50.0 mL sample of a methylamine solution and determines the pH

  2. science

    I am doing a titration lab and need help with a problem. (i used .100M H2SO4)(I used 10.0 ml of Ba(OH)2 solution and added 50.0 ml of distilled water making 60.0 ml total.) 1. Use the titration results to calculate the moles of

  3. AP Chemistry

    CH3NH2(aq)+H2O(l)=>CH3NH3+(aq)+OH-(aq) Kb=4.4 x 10^-4 Methylamine, CH3NH2, is a weak base that reacts with water according to the equation above. A student obtains a 50.0 mL sample of a methylamine solution and determines the pH

  4. Chemistry

    HC2H3O2 + NaOH --> NaC2H3O2 + H2O? a. when the titration is only half over, what species are present in the reaction flask b. what can be said about the pH at this point when the titration is half over? c. what is the pH at the

  1. Science

    C6H5NH2 + H2O C6H5NH3+ + OH- 1. Aniline, a weak base, reacts with water according to the rxn above. a. A sample of aniline is dissolved in water to produce 25.0 ml of a .10 M soln. The pH of soln is 8.82. What is Kb for this

  2. chemistry

    Calculate the pH for each of the following points in the titration of 50.0 mL of a 1.8 M H3PO3(aq) with 1.8 M KOH(aq). before KOH after addition of 25, 50,75,100 ml KOH

  3. Chemistry Titration Lab HELP!

    Hi everyone! I just got a new lab that I MUST complete today, and it's about titration- I have absolutely no clue how to do it, it just doesn't make sense to me! I hope that someone can help explain to me how to do it so I can

  4. AP Chemistry

    A solution of sodium hydroxide is standardized against potassium hydrogen phthalate (KHP, formula weight 204.2 g/mol). From the following data, calculate the molarity of the NaOH solution: mass of KHP 1.234 g; buret reading before

  1. Biotechnology

    Consider the titration of 25.0 mL of 0.050 0 M Sn2+ with 0.100 M Fe3+ in 1 M HCl to give Fe2+ and Sn4+, using Pt and calomel electrodes. (a) Write a balanced titration reaction. (b) Write two half-reactions for the indicator

  2. chemistry

    In the titration of Na2S2O3 against KIO3 the average titre value was 23.1cm3,the volume of iodine used in the titration was 25cm3 and the concentration of Na2S2O3 was 0.1M.calculate the molarity of KIO3

  3. Chemistry

    In the titration of 20.00 mL of 0.175 M NaOH, calculate the number of milliliters of 0.200 M HCl that must be added to reach a pH of 12,55. I know the answer is 11,9 mL but I don't know how to calculate it.

  4. Chemistry

    Calculate the pH values and draw the titration curve for the titration of 500 mL of 0.010 M acetic acid (pKa 4.76) with 0.010 MKOH. Calculate the pH of the solution after 490 mL of the titrant have been added.

You can view more similar questions or ask a new question.