Chemistry

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TRUE OR FALSE?

1) A solution that is made out of 1.00mol/L ammonia and 0.50mol/L of ammonium chloride is a basic buffer.

2) The pH at the equivalence point of a weak base with a strong acid is expected to be less than 7 because the acid that is added is very strong

3) The pH of a buffer solution made out of 0.20mol/L hydrofluoric acid and 0.30mol/L sodiumfluoride is the same as a buffer solution that is made out of 0.10mol/L of acetic acid and 0.15mol/L of sodium acetate.

4) One cannot prepare a buffer from a strong acid and its conjugated base, because a conjugated base of a strong acid cannot buffer; meaning cannot react in the reverse direction of the acid dissociation.

5) The pH at the equivalence point of a weak base with a strong acid is expected to be less than 7 because of the presentce of the conjugated acid in the water.

6) You cannot prepare a buffer from nitric acid and sodium nitrate, but you can make one from nitrous acid and potassium nitrite

7) A solution that is made out of 1.00mol/L ammonia and 0.05mol/L of ammonium chloide can act as a basic buffer.

8) You cannot prepare a buffer with a pH of 11.5 with trimethylamine and trimethylammonium chloride

9) The capacity of a buffer solution made out of 0.20mol/L hydrofluoric acid and 0.30mol/L sodiumfluoride is the higher than that of a buffer solution made out of 0.10mol/L of hydrofluoric acid and 0.15mol/L of sodiumfluoride. But the pH of the two buffers solutions is the same.

I thought it was: true, false, false, true, true true, true, false, false, but it was not the good answer. I've been stuck on this for a looong time, help please!

  • Chemistry -

    1) A solution that is made out of 1.00mol/L ammonia and 0.50mol/L of ammonium chloride is a basic buffer.

    pH = pKa + log(base/acid)
    pH = 9.25 + log(1.00/0.5)
    pH = 9.55
    basic.

  • Chemistry -

    2) The pH at the equivalence point of a weak base with a strong acid is expected to be less than 7 because the acid that is added is very strong

    WB/SA = say NH4Cl. That will be acidic because the NH4^+ is hydrolyzed to produce H3O^+
    NH4^+ + H2O ==> H3O^+ + NH3
    It is acidic but and I even agree to some extent with the strong acid part but I would count it false because I think they want the answer of the hydrolysis of NH4^+.

  • Chemistry -

    3) The pH of a buffer solution made out of 0.20mol/L hydrofluoric acid and 0.30mol/L sodiumfluoride is the same as a buffer solution that is made out of 0.10mol/L of acetic acid and 0.15mol/L of sodium acetate.

    HF:
    pH = 3.14 + log(0.3/0.2) = 3.33
    HAc:
    pH = 4.75 + log(0.15/0.1) = 4.93
    false

  • Chemistry -

    I don't know why the conjugate base can't react (for example Cl^- can react with Ag^+ to form AgCl);however I would go the statement as true.

  • Chemistry -

    Your other answers look ok to me also; I suspect the outlier may be those where part of the statement is true and part is not true and we must make a guess as to which is right. Sorry I'm not of more help.

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