chemistry

posted by .

When excess solid Mg(OH)2 is shaken with 1.00 L of 1.2 M NH4Cl solution, the resulting saturated solution has pH = 9.30. Calculate the Ksp of Mg(OH)2

I am not sure where to even begin on this problem.

  • chemistry -

    3.3x10^-11

  • chemistry -

    how did you get that?

  • chemistry -

    can anyone please explain how to solve this?

  • chemistry -

    To begin the problem, I calculated the [OH-] from the pH.
    14-9.3 = 4.7 pOH,
    [OH-] = 10^-(4.7) = 1.995x10^-5
    Here's where things get difficult. NH4Cl breaks apart in water into NH4+ and Cl-. Therefore we can say the 1.2M is the concentration of NH4+. NH4+ combines with OH to form NH3 and H2O.

    NH4+(aq)+OH-(aq) <-> NH3(aq)+H2O(l)
    This equation is the equation for finding the Kb of NH3, but backward. Since we know that in order to flip a chemical equilibrium equation, we have to invert the K value,

    Kb(NH3)=1.8x10^-5, Kb(NH3,rev)=5.6x10^4

    Looking back at the equilibrium expression for NH4+ and OH- combining, we can solve an equilibrium to figure out what the OH had to be in the beginning in order to have excess [OH-] of 1.995x10^-5 M.

    NH4+(aq)+OH-(aq) <-> NH3(aq)+H2O(l)
    1.2M ? 0
    -x -x +x
    1.2-x 2.0x10^-5 x

    5.6x10^4= x / (2.0x10^-5 x (1.2 - x))
    x = 0.63398

    So the [OH-] before NH4+ reacted with it was 0.63396 + 2x10^-5 = 0.63398

    Now we work backward again and set up an ICE chart for the dissociation of Mg(OH)2.

    Mg(OH)2(s) <-> Mg2+(aq)+2 OH-(aq)
    N/A 0 0
    N/A +x +2x
    N/A ? 0.63398

    In order to obtain 0.63398 as an answer, the change (x) must be 0.63398 / 2, making [Mg2+]= 0.317.

    Ksp(Mg(OH)2)= [Mg2+]x[OH-]^2
    Ksp = (0.317) x (2x10^-5)^2 = 1.262x10^-10 for this particular problem.

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. CHEMISTRY

    Wondering If I did this correctly so far 50.0 ml of a 0.0500 M solution of lead (II) nitrate is mixed with 40.0 ml of a 0.200 M solution of sodium iodate at 25°C. Calculate the Pb2+ and IO3- concentrations when the mixture comes to …
  2. Chemistry (urgent)

    Hi, I have a few chemistry problems that I'm having trouble solving. I put my attempted solutions after the problems in *'s. There was one problem I had no idea how to solve. What concentration of silver chromate (Ksp = 9.0 x 10-12) …
  3. CHEMISTRY--PLEASE HELP, URGENT

    A saturated solution of CaSO4(aq) is made in a beaker until there is excess calcium sulfate resting at the bottom. Then solid potassium sulfate is added. Which of the following is true?
  4. chemistry

    A saturated solution of Mg(OH)2 is prepared having a large excess of Mg(OH)2. Sn(NO3)2 is added to the solution. Ksp = 1.9 10-11 for Mg(OH)2 and Ksp = 6.0 10-26 for Sn(OH)2.
  5. Chemistry

    A saturated solution of Mg(OH)2 is prepared having a large excess of Mg(OH)2. Sn(NO3)2 is added to the solution. Ksp = 1.9 x 10^-11 for Mg(OH)2 and Ksp = 6.0x10^-26 for Sn(OH)2. What [Sn2+] is required so that the [Mg2+] in solution …
  6. Chemistry

    At 22 °C an excess amount of a generic metal hydroxide M(OH)2, is mixed with pure water. The resulting equilibrium solution has a pH of 10.56. What is the Ksp of the compound at 22 °C?
  7. JHU

    When excess solid Mg(OH)2 is shaken with 1.00 L of 1.2 M NH4Cl solution, the resulting saturated solution has pH = 9.30. Calculate the Ksp of Mg(OH)2
  8. Chemistry

    When excess solid Mg(OH)2 is shaken with 1.00 L of 1.2 M NH4Cl solution, the resulting saturated solution has pH = 9.30. Calculate the Ksp of Mg(OH)2
  9. Chemistry - help please

    In an experiment, when 25 mL of 5.5 x 10^-3 M NaOH is mixed with 30 mL of 7.5 x 10^-3 M Fe(Br)2, a hydroxide compound is formed (Ksp = 1.8 x 10^15). Which of the following describes the resulting solution?
  10. chem

    the following experiment was performed in the laboratory : an excess of solid SrCrO4 is vigorously shaken in water until a saturated solution is obtained. The excess solid is filtrated from the solution and 25.00 ml of the solution …

More Similar Questions