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Chapter 15: Problem 4
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A certain buffer is made by dissolving \(\mathrm{NaHCO}_{3}\) and \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) in some water. Write equations to show how this buffer neutralizes added \(\mathrm{H}^{+}\) and \(\mathrm{OH}^{-}\) .
A \(0.400-M\) solution of ammonia was titrated with hydrochloric acid to the equivalence point, where the total volume was 1.50 times the original volume. At what pH does the equivalence point occur?
Repeat the procedure in Exercise \(67,\) but for the titration of 25.0 \(\mathrm{mL}\) of 0.100\(M\) pyridine with 0.100\(M\) hydrochloric acid \(\left(K_{\mathrm{b}} \text { for pyridine is } 1.7 \times 10^{-9}\right) .\) Do not calculate the points at 24.9 and 25.1 \(\mathrm{mL}\)
Consider the titration of 100.0 \(\mathrm{mL}\) of 0.10 $\mathrm{M} \mathrm{H}_{3} \mathrm{AsO}_{4}\( by 0.10 \)M \mathrm{NaOH}$ . What are the major species present at 50.0 \(\mathrm{mL}\) of \(\mathrm{NaOH}\) added? How would you calculate the pH at this point? Answer the same questions for 150.0 \(\mathrm{mL}\) of NaOH added. At what volume of NaOH added does pH $=\mathrm{p} K_{\mathrm{a}_{\mathrm{i}}} ?$
Tris (hydroxymethyl)aminomethane, commonly called TRIS or Trizma, is often used as a buffer in biochemical studies. Its buffering range is $\mathrm{pH} 7\( to \)9,\( and \)K_{\mathrm{b}}\( is \)1.19 \times 10^{-6}$ for the aqueous reaction $$ \left(\mathrm{HOCH}_{2}\right)_{3} \mathrm{CNH}_{2}+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons\left(\mathrm{HOCH}_{2}\right)_{3} \mathrm{CNH}_{3}^{+}+\mathrm{OH}^{-} $$ a. What is the optimal pH for TRIS buffers? b. Calculate the ratio \([T R I S] /\left[T R I S H^{+}\right]\) at \(p H=7.00\) and at p H=9.00 c. A buffer is prepared by diluting 50.0 \(\mathrm{g}\) TRIS base and 65.0 \(\mathrm{g}\) TRIS hydrochloride (written as TRISHCl) to a total volume of 2.0 \(\mathrm{L}\) What is the pH of this buffer? What is the pH after 0.50 \(\mathrm{mL}\) of 12 \(\mathrm{MHCl}\) is added to a 200.0 -mL portion of the buffer?
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