Chapter 16

Why does a solution of a weak acid and its conjugate base control pH better than a solution of the weak acid alone?

Why does a solution of a weak base and its conjugate acid control pH better than a solution of the weak base alone?

Identify a suitable buffer system to maintain a pH of 3.0 in an aqueous solution.

Identify a suitable buffer system to maintain a pH of 3.0 in an aqueous solution.

What does "buffer capacity" mean?

What effect does adding more NaF have on the pH and buffer capacity of an aqueous solution that is initially \(1.0 \mathrm{MHF}\) and \(0.50 \mathrm{M} \mathrm{NaF} ?\)

Three buffers are separately prepared using equal concentrations of formic acid and sodium formate, hydrofluoric acid and sodium fluoride, and acetic acid and sodium acetate. Rank the three buffers from highest to lowest pH.

Equal volumes of two buffers are prepared with equal concentrations of acid and conjugate base, but they use different weak acids with different p \(K_{\mathrm{a}}\) values. Do the two buffers have the same buffer capacity?

How does diluting a \(\mathrm{pH}=4.00\) buffer with an equal volume of pure water affect its pH?

Buffer A contains nearly equal concentrations of its conjugate acid-base pair. Buffer \(\mathrm{B}\) contains the same total concentration of acidic and basic components as buffer \(\mathrm{A}\) but B has twice as much of its weak acid as its conjugate base. Which buffer experiences a smaller change in \(\mathrm{pH}\) when a. the same small quantity of strong base is added to both? b. the same small quantity of strong acid is added to both?

What is the pH of a buffer that is \(0.200 M\) chloroacetic acid and \(0.100 M\) sodium chloroacetate at \(25^{\circ} \mathrm{C} ?\)

What is the pH of a buffer that is \(0.100 M\) methylamine and \(0.175 M\) methylammonium chloride at \(25^{\circ} \mathrm{C} ?\)

What is the pH of a buffer that is \(0.110 M \mathrm{HPO}_{4}^{2-}\) and \(0.220 \mathrm{M} \mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) at \(25^{\circ} \mathrm{C} ?\)

What is the pH of a buffer that is \(0.200 M \mathrm{H}_{2} \mathrm{SO}_{3}\) and \(0.250 \mathrm{M} \mathrm{NaHSO}_{3}\) at \(25^{\circ} \mathrm{C} ?\)

What is the mole ratio of ammonia to ammonium chloride in a buffer with a pH of \(9.00 ?\)

What masses of bromoacetic acid and sodium bromoacetate are needed to prepare \(1.00 \mathrm{L}\) of \(\mathrm{pH}=3.00\) buffer if the total concentration of the two components is \(0.200 M ?\)

What masses of acetic acid and sodium acetate are needed to prepare \(125 \mathrm{mL}\) of \(\mathrm{pH}=5.00\) buffer if the total concentration of the two components is \(0.500 M ?\)

What masses of dimethylamine and dimethylammonium chloride do you need to prepare \(0.500 \mathrm{L}\) of \(\mathrm{pH}=11.00\) buffer if the total concentration of the two components is \(0.300 M ?\)

What masses of ethylamine and ethylammonium chloride do you need to prepare \(1.00 \mathrm{L}\) of \(\mathrm{pH}=10.50\) buffer if the total concentration of the two components is \(0.250 M ?\)

What is the \(\mathrm{pH}\) at \(25^{\circ} \mathrm{C}\) of a solution that results from mixing equal volumes of \(0.05 M\) solution of ammonia and a \(0.025 M\) solution of hydrochloric acid?

What is the pH at \(25^{\circ} \mathrm{C}\) of a solution that results from mixing equal volumes of a \(0.05 M\) solution of acetic acid and a \(0.025 M\) solution of sodium hydroxide?

What volume of \(0.422 M\) NaOH must be added to \(0.500 \mathrm{L}\) of \(0.300 M\) acetic acid to raise its \(\mathrm{pH}\) to 4.00 at \(25^{\circ} \mathrm{C} ?\)

What volume of \(1.16 M\) HCl must be added to 0.250 L of \(0.350 M\) dimethylamine to produce a buffer with a pH of 10.75 at \(25^{\circ} \mathrm{C} ?\)

A buffer consists of \(0.120 \mathrm{MHNO}_{2}\) and \(0.150 \mathrm{MNaNO}_{2}\) at \(25^{\circ} \mathrm{C}\) a. What is the pH of the buffer? b. What is the pH after the addition of 1.00 mL of \(11.6 M\) HCl to 1.00 L of the buffer solution?

A buffer is prepared by mixing \(50.0 \mathrm{mL}\) of \(0.200 M \mathrm{NaOH}\) with \(100.0 \mathrm{mL}\) of \(0.175 M\) acetic acid. a. What is the pH of the buffer? b. What is the pH of the buffer after \(1.00 \mathrm{g} \mathrm{NaOH}\) is dissolved in it?

Do all titrations of samples of strong monoprotic acids with solutions of strong bases have the same pH at their equivalence points? Explain why or why not.

Do all titrations of samples of weak monoprotic acids with solutions of strong bases have the same \(\mathrm{pH}\) at their equivalence points? Explain why or why not.

Describe two properties of phenolphthalein that make it a good choice as an indicator for detecting the first equivalence point in an alkalinity titration.

Phenolphthalein can be used as a color indicator to detect the equivalence points of titrations of samples containing either weak acids or strong acids, even though the pH values of the equivalence points vary depending on the identity of the acid. Explain how this is possible.

In the titration of a solution of a weak monoprotic acid with a standard solution of \(\mathrm{NaOH}\), the \(\mathrm{pH}\) halfway to the equivalence point was \(4.44 .\) In the titration of a second solution of the same acid, exactly twice as much of the standard solution of \(\mathrm{NaOH}\) was needed to reach the equivalence point. What was the \(\mathrm{pH}\) halfway to the equivalence point in this titration?

The \(\mathrm{pH}\) of a solution of a strong monoprotic acid is lower than the pH of an equal concentration of a weak monoprotic acid, yet equal volumes of both require the same volume of basic titrant to reach the equivalence point. Explain why.

A \(25.0 \mathrm{mL}\) sample of \(0.100 M\) acetic acid is titrated with \(0.125 \mathrm{M} \mathrm{NaOH}\) at \(25^{\circ} \mathrm{C} .\) What is the \(\mathrm{pH}\) of the solution after \(10.0,20.0,\) and \(30.0 \mathrm{mL}\) of the base have been added?

A \(25.0 \mathrm{mL}\) sample of a \(0.100 M\) solution of aqueous trimethylamine is titrated with a \(0.125 M\) solution of \(\mathrm{HCl}\) at \(25^{\circ} \mathrm{C} .\) What is the pH of the solution after 10.0,20.0 and 30.0 mL of acid have been added?

Sketch a titration curve for the titration of \(50.0 \mathrm{mL}\) of \(0.200 \mathrm{MHNO}_{2}\) with \(1.00 \mathrm{MNaOH.}\) What is the pH of the sample after \(2.50,5.00,7.50,\) and \(10.00 \mathrm{mL}\) of titrant have been added?

Sketch a titration curve for the titration of \(40.0 \mathrm{mL}\) of a \(0.100 M\) solution of oxalic acid with a \(0.100 M\) solution of NaOH. What is the pH of the titration reaction mixture after \(10.0,20.0,30.0,\) and \(40.0 \mathrm{mL}\) of titrant have been added?

What volume of \(0.100 M\) HCl is required to titrate \(250 \mathrm{mL}\) of \(0.0100 M \mathrm{Na}_{2} \mathrm{CO}_{3}\) to the first equivalence point?

What volume of \(0.0100 M\) HCl is required to titrate \(250 \mathrm{mL}\) of \(0.0100 M \mathrm{Na}_{2} \mathrm{CO}_{3}\) and \(250 \mathrm{mL}\) of \(0.0100 \mathrm{MHCO}_{3}^{-} ?\)

(a) What is the concentration of ammonia in a popular window cleaner if \(25.34 \mathrm{mL}\) of \(1.162 \mathrm{M} \mathrm{HCl}\) is needed to titrate a \(10.00 \mathrm{mL}\) sample of the cleaner? (b) Suppose that the sample was diluted to about \(50 \mathrm{mL}\) with deionized water prior to the titration to make it easier to mount a pH electrode in it. What effect did this dilution have on the volume of titrant needed?

In an alkalinity titration of a \(100.0 \mathrm{mL}\) sample of water from a hot spring, \(2.56 \mathrm{mL}\) of a \(0.0355 M\) solution of HCl is needed to reach the first equivalence point \((\mathrm{pH}=8.3)\) and another \(10.42 \mathrm{mL}\) is needed to reach the second equivalence point \((\mathrm{pH}=4.0) .\) If the alkalinity of the spring water is due only to the presence of carbonate and bicarbonate, what are the concentrations of each?

For each titration, predict whether the pH of the equivalence point is less than, equal to, or greater than 7 a. Quinine titrated with nitric acid b. Pyruvic acid titrated with calcium hydroxide c. Hydrobromic acid titrated with strontium hydroxide

For each titration, predict whether the pH of the equivalence point is less than, equal to, or greater than 7 a. HCN titrated with \(\mathrm{Ca}(\mathrm{OH})_{2}\) b. LiOH titrated with HI c. \(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{N}\) titrated with \(\mathrm{KOH}\)

When \(100 \mathrm{mL}\) of \(0.0125 \mathrm{M}\) ascorbic acid is titrated with \(0.010 M \mathrm{NaOH},\) how many equivalence points will the titration curve have, and what \(\mathrm{pH}\) indicator(s) could be used? Refer to Figure 16.5 for the colors of indicators.

Red cabbage juice is a sensitive acid-base indicator; its colors range from red at acidic pH to yellow in alkaline solutions. What color would red cabbage juice have at the equivalence point when 25 mL of a \(0.10 M\) solution of acetic acid is titrated with \(0.10 \mathrm{M} \mathrm{NaOH} ?\)

Are all Lewis bases also Brensted-Lowry bases? Explain why or why not.

Are all Brensted-Lowry bases also Lewis bases? Explain why or why not.

Are all Brensted-Lowry acids also Lewis acids? Explain why or why not.

Why is \(\mathrm{BF}_{3}\) a Lewis acid but not a Bronsted-Lowry acid?

Draw Lewis structures that show how electron pairs move and bonds form and break during the autoionization of water. Label the appropriate \(\mathrm{H}_{2} \mathrm{O}\) molecules as the Lewis acid and Lewis base.

Draw Lewis structures that show how electron pairs move and bonds form and break in the following reaction, and identify the Lewis acid and Lewis base. $$ \mathrm{MgO}(s)+\mathrm{CO}_{2}(g) \rightarrow \mathrm{MgCO}_{3}(s) $$

Draw Lewis structures that show how electron pairs move and bonds form and break in the following reaction, and identify the Lewis acid and Lewis base. $$ \mathrm{SO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow \mathrm{H}_{2} \mathrm{SO}_{3}(a q) $$