Acid-Base Titrations

AP Chemistry· difficulty 4/5

half-eq eq pt Volume NaOH (mL) pH

25.00 mL of 0.100 M acetic acid (Ka=1.8×105K_a = 1.8\times 10^{-5}) is titrated with 0.100 M NaOH. What is the pH at the equivalence point?

  • A

    pH5.27pH \approx 5.27

  • B

    pH=7.00pH = 7.00

  • C

    pH8.72pH \approx 8.72

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  • D

    pH4.74pH \approx 4.74

Explanation

At eq pt, all acid converted to acetate; volume = 50.00 mL, [A][A^-] = 0.0500 M. KbK_b = Kw/KaK_w/K_a = 5.56e-10. [OH][OH^-] = (5.56e10)(0.05)\sqrt{(5.56e-10)(0.05)} = 5.27e-6. pOH = 5.28, pH = 8.72.

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