Problem 97
The compound para-aminobenzoic acid (PABA) is a powerful sun-screening agent whose salts were once used widely in sun tanning and screening lotions. The parent acid, which we may symbolize as \(\mathrm{H}-\mathrm{Paba}\), is a weak acid with a \(\mathrm{p} K_{\mathrm{a}}\) of 4.92 (at \(25^{\circ} \mathrm{C}\) ). What are the \(\left[\mathrm{H}^{+}\right]\) and \(\mathrm{pH}\) of a \(0.030 \mathrm{M}\) solution of this acid?
Problem 106
The conjugate acid of a molecular base has the general formula \(B \mathrm{H}^{+}\) and a \(\mathrm{p} K_{\mathrm{a}}\) of \(5.00 .\) A solution of a salt of this cation, \(B \mathrm{H} Y\), tests slightly basic. Will the conjugate acid of \(Y^{-}, \mathrm{H} Y\), have a \(\mathrm{p} K_{\mathrm{a}}\) greater than 5.00 or less than 5.00? Explain.
Problem 107
What is the \(\mathrm{pH}\) of a solution that contains \(0.15 \mathrm{M}\) \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\) and \(0.25 \mathrm{M} \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}^{-}\) ? Use \(K_{\mathrm{a}}=1.8 \times\) \(10^{-5}\) for \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\)
Problem 138
For the titration of \(50.00 \mathrm{~mL}\) of \(0.1000 \mathrm{M}\) ammonia with \(0.1000 \mathrm{M} \mathrm{HCl}\), calculate the \(\mathrm{pH}\) (a) before the addition of any HCl solution, (b) after \(20.00 \mathrm{~mL}\) of the acid has been added, (c) after half of the \(\mathrm{NH}_{3}\) has been neutralized, and (d) at the equivalence point.
Problem 150
For the titration of \(25.00 \mathrm{~mL}\) of \(0.1000 \mathrm{M} \mathrm{HCl}\) with \(0.1000 \mathrm{M} \mathrm{NaOH},\) calculate the \(\mathrm{pH}\) of the reaction mixture after each of the following total volumes of base have been added to the original solution. (Remember to take into account the change in total volume.) Construct a graph showing the titration curve for this experiment. (d) \(24.99 \mathrm{~mL}\) (g) \(25.10 \mathrm{~mL}\) (b) \(10.00 \mathrm{~mL}\) (e) \(25.00 \mathrm{~mL}\) (h) \(26.00 \mathrm{~mL}\) (c) \(24.90 \mathrm{~mL}\) (f) \(25.01 \mathrm{~mL}\) (i) \(50.00 \mathrm{~mL}\)
Problem 156
Suppose \(38.0 \mathrm{~mL}\) of \(0.000200 \mathrm{M} \mathrm{HCl}\) is added to \(40.0 \mathrm{~mL}\) of \(0.000180 \mathrm{M} \mathrm{NaOH}\). What will be the \(\mathrm{pH}\) of the final mixture?
Problem 163
In the 1950 s it was discovered that lakes in the northeastern United States had declining fish populations due to increased acidity. In order to address the problem of lake acidification, make a list of what you need to know in order to start addressing the problem.
Problem 165
Why must the acid used for a buffer have a \(\mathrm{p} K_{\mathrm{a}}\) within one \(\mathrm{pH}\) unit of the \(\mathrm{pH}\) of the buffer? What happens if that condition is not met?
