At what point in the following titration curve for a weak acid being titrated wi

Question

At what point in the following titration curve for a weak acid being titrated with a strong base is the pH equal to the pK_a of the acid? The x-axis scale goes from 0.0 mL to 20.0 mL. The sharp rise is at 10.0 mL. a. 0.0 mL. b. 5.0 mL. c. 9.0 mL d 10.0 mL. c. 18.0 mL A 25.0 mL solution of quinine was titrated with 1.00 M hydrochloric acid. HCI. It was found that the solution contained 0.125 moles of quinine. What was the pH of the solution after 50.00 mL of the 11C1 solution were added? Quinine is monobasic with pK_b = 5.10. a. 5.10 b. 890 c. 8.72 d. 4.92 e. 9.08 Glycolic acid, which is a monoprotic acid and a constituent in sugar cane, has a pK, of 3.9. A 25.0 mL solution of glycolic acid is titrated to the stoichiometric point with 35.8 ml. of 0.020 M sodium hydroxide solution. What is the pi I of the resulting solution at the stoichiometric point? a. 4.12 b 9.88 c. 6.01 d. 7.9 8 c. Sufficient information is not provided to determine the pH. A solution of nitrous acid (0.13 M, 20.00 mL) was titrated with 18.0 mL of 0.12 M sodium hydroxide (K_a of nitrous acid = 4.00 times 10^-4). What is the final pH of this solution? a. 2.71 b. 4.09 c. 5.34 d. 11.29 e. 9.91

Explanation / Answer

Question 16.

Recall that

pH = pKa is only valid when:

this is a buffer, so weak acid + conjguate base are present

not nly that

Conjugate base = weak acid concentration

so

this is only in the HALF equivalence point

the equivalence point is given at V = drastic change in pH

so

Veq = 10 mL, approx

so

Veq half = 1/2*10 = 5 mL

the pH when V = 5 mL

pH = 4.5 approx (hard to see)

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