Chapter 15

What is the pH of \(5.00 \times 10^{-4} \mathrm{MH}_{2} \mathrm{SO}_{4} ?\)

Rhubarb Pie The leaves of the rhubarb plant contain high concentrations of diprotic oxalic acid (HOOCCOOH) and must be removed before the stems are used to make rhubarb pie. What is the pH of \(0.0288 M\) oxalic acid?

Nicotine Addiction Nicotine is responsible for the addictive properties of tobacco. What is the \(\mathrm{pH}\) of \(1.00 \times 10^{-3} \mathrm{M}\) nicotine?

How is it that aqueous solutions of \(\mathrm{NaF}\) are basic, but solutions of \(\mathrm{NaCl}\) are neutral?

Why is it unnecessary to publish tables of \(K_{\mathrm{b}}\) values of the conjugate bases of weak acids whose \(K_{\mathrm{a}}\) values are known?

Which of the following salts produces an acidic solution in water: ammonium acetate, ammonium nitrate, or sodium formate?

Which of the following salts produces a basic solution in water: \(\mathrm{NaNO}_{2}, \mathrm{KNO}_{3},\) or \(\mathrm{NH}_{4} \mathrm{Cl} ?\)

Neutralizing the Smell of Fish Trimethylamine, \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{N}\) \(\left(K_{\mathrm{b}}=6.5 \times 10^{-5} \text {at } 25^{\circ} \mathrm{C}\right),\) contributes to the "fishy" odor of not-so-fresh seafood. Some people squeeze fresh lemon juice (which contains a high concentration of citric acid) on cooked fish to reduce the fishy odor. Why is this practice effective?

The \(K_{\mathrm{a}}\) of the conjugate acid of the artificial sweetener saccharin is \(2.1 \times 10^{-11} .\) What is the p \(K_{h}\) for saccharin?

The \(K_{a_{1}}\) value for oxalic acid (HOOCCOOH) is \(5.9 \times 10^{-2},\) and the \(K_{2,}\) value is \(6.4 \times 10^{-5} .\) What are the values of \(K_{\mathrm{b}_{1}}\) and \(K_{\mathrm{b}_{2}}\) of the oxalate anion \(\left(-\mathrm{OOCCOO}^{-}\right) ?\)

Dental Health Sodium fluoride is added to many municipal water supplies to reduce tooth decay. Calculate the pH of \(0.00339 M\) NaF at \(25^{\circ} \mathrm{C}\)

Calculate the pH of \(1.25 \times 10^{-2} \mathrm{M}\) of the decongestant ephedrine hydrochloride if the \(\mathrm{p} K_{\mathrm{b}}\) of ephedrine (its conjugate base) is 3.86

Consider the following compounds: \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) \(\mathrm{CH}_{3} \mathrm{COOH}, \mathrm{Ca}(\mathrm{OH})_{2},\) and \(\mathrm{HClO}_{4}\) a. Identify the Arrhenius acid(s). b. Identify the Arrhenius base(s). c. Identify the Bronsted-Lowry acid(s). d. Identify the Brensted-Lowry base(s).

Are all Arrhenius acids also Bronsted-Lowry acids? Are all Bronsted-Lowry acids also Arrhenius acids? If yes, explain why. If not, give a specific example to demonstrate the difference.

Are all Arrhenius bases also Bronsted-Lowry bases? Are \(15.9=\) all Bronsted-Lowry bases also Arrhenius bases? If yes, explain why. If not, give a specific example to demonstrate the difference.

Describe the intermolecular forces and changes in bonding that lead to the formation of a basic solution when methylamine (CH \(_{3} \mathrm{NH}_{2}\) ) dissolves in water.

Describe the chemical reactions of sulfur that begin with the burning of high- sulfur fossil fuel and that end with the reaction between acid rain and building exteriors made of marble \(\left(\mathrm{CaCO}_{3}\right)\)

The \(K_{z_{1}}\) of phosphorous acid, \(\mathrm{H}_{3} \mathrm{PO}_{3},\) is nearly the same as the \(K_{\mathrm{a}_{1}}\) of phosphoric acid, \(\mathrm{H}_{3} \mathrm{PO}_{4}\) a. Draw the Lewis structure of phosphorous acid. b. Identify the ionizable hydrogen atoms in the structure. c. Explain why the \(K_{a_{1}}\) values of phosphoric acid and phosphorous acid are similar.

Ocean Acidification Some climate models predict a decrease in the pH of the oceans of 0.3 to \(0.5 \mathrm{pH}\) unit by 2100 because of increases in atmospheric carbon dioxide. a. Explain, by using the appropriate chemical reactions and equilibria, how an increase in atmospheric \(\mathrm{CO}_{2}\) could produce a decrease in oceanic pH. b. How much more acidic would the oceans be if their pH dropped this much? c. Oceanographers are concerned about the impact of a drop in oceanic pH on the survival of coral reefs. Why?

Sulfuric acid reacts with nitric acid as shown below: \(\mathrm{HNO}_{3}(a q)+2 \mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow \mathrm{NO}_{2}^{+}(a q)+\mathrm{H}_{3} \mathrm{O}^{+}(a q)+2 \mathrm{HSO}_{4}^{-}(a q)\) a. Is the reaction a redox process? b. Identify the acid, base, conjugate acid, and conjugate base in the reaction. (Hint: Draw the Lewis structures for each.

Thiosulfuric acid, \(\mathrm{H}_{2} \mathrm{S}_{2} \mathrm{O}_{3},\) can be prepared by the reaction of \(\mathrm{H}_{2} \mathrm{S}\) with \(\mathrm{HSO}_{3} \mathrm{Cl}:\) $$\mathrm{HSO}_{3} \mathrm{Cl}(\ell)+\mathrm{H}_{2} \mathrm{S}(g) \rightarrow \mathrm{HCl}(g)+\mathrm{H}_{2} \mathrm{S}_{2} \mathrm{O}_{3}(\ell)$$ a. Draw a Lewis structure for \(\mathrm{H}_{2} \mathrm{S}_{2} \mathrm{O}_{3},\) given that it is isostructural with \(\mathrm{H}_{2} \mathrm{SO}_{4}\) b. Do you expect \(\mathrm{H}_{2} \mathrm{S}_{2} \mathrm{O}_{3}\) to be a stronger or weaker acid than \(\mathrm{H}_{2} \mathrm{SO}_{4} ?\) Explain your answer.

Which of these solutions is the most acidic? Which is the most basic? i. \(1.0 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{3}\) ii. \(0.10 M \mathrm{H}_{2} \mathrm{SO}_{4}\) iii. \(0.30 M \mathrm{NaHSO}_{4}\) iv. \(0.30 M \mathrm{Na}_{2} \mathrm{SO}_{4}\) v. \(0.30 M \mathrm{Na}_{2} \mathrm{SO}_{3}\)

Predict which solution in each pair below will have the lower pH. a. \(2.56 \times 10^{-2} \mathrm{M} \mathrm{HCl}\) or \(4.09 \times 10^{-2} \mathrm{MHBr}\) b. \(1.00 \times 10^{-5} M\) acctic acid \(\left(K_{\mathrm{a}}=1.76 \times 10^{-5}\right)\) or \(1.00 \times 10^{-5} M\) formic acid \(\left(K_{a}=1.77 \times 10^{-4}\right)\) c. \(22 \mathrm{mM} \mathrm{CH}_{3} \mathrm{NH}_{2}\left(\mathrm{p} K_{\mathrm{b}}=3.36\right)\) or \(22 \mathrm{mM}\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH}\left(K_{\mathrm{b}}=5.9 \times 10^{-4}\right)\) d. \(158 \mathrm{mM} \mathrm{NH}_{3}\left(\mathrm{p} K_{\mathrm{b}}=4.75\right)\) or \(158 \mathrm{m} M\) acetic acid \(\left(p K_{a}=4.75\right)\) e. \(0.00395 M \mathrm{HNO}_{3}\) or \(0.00145 M \mathrm{HClO}_{4}\) f. \(2.05 \times 10^{-1} M\) propionic acid \(\left(K_{2}=1.4 \times 10^{-5}\right)\) or \(2.05 \times 10^{-1} M\) fluoroacetic acid \(\left(K_{2}=2.6 \times 10^{-3}\right)\) g. 375 m \(M\) pyridine \(\left(p K_{b}=8.77\right)\) or \(375 \mathrm{mM}\) aniline \(\left(\mathrm{p} K_{\mathrm{b}}=9.40\right)\) h. \(0.555 M \mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}^{3+}\left(K_{2}=3 \times 10^{-3}\right)\) or \(0.355 M \mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}^{3+}\left(K_{2}=1 \times 10^{-4}\right)\)

The value of \(K_{w}\) increases as temperature increases. a. If the \(\mathrm{p} K_{\mathrm{w}}=13.017\) at \(60^{\circ} \mathrm{C},\) what is the \(\left[\mathrm{H}^{+}\right] ?\) b. What is the pH of water at \(60^{\circ} \mathrm{C} ?\)

Calculate the indicated value based on the information given: a. What is the \(K_{\mathrm{b}}\) of the lactate ion? The \(K_{\mathrm{a}}\) of lactic acid is \(1.4 \times 10^{-4}\) b. What is the \(K_{\mathrm{b}}\) of the conjugate base of pyruvic acid? The \(K_{a}\) of pyruvic acid is \(2.8 \times 10^{-3} .\) c. What is the \(K_{2}\) of the conjugate acid of aniline? Aniline has a \(K_{\mathrm{b}}\) of \(5.9 \times 10^{-4}\) d. Quinine has two basic nitrogen atoms in its structure. The \(K_{\mathrm{b}}\) of the most basic nitrogen atom is \(3.3 \times 10^{-6} .\) What is the \(K_{a}\) of the HCl salt of that nitrogen atom?

Identify the conjugate base for the following weak acids and calculate \(K_{\mathrm{b}}\) for each. Which conjugate base is the strongest? a. \(\mathrm{ClCH}_{2} \mathrm{COOH}\) b. \(\mathrm{NH}_{4}^{+}\) c. HCN d. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\)

For each of the molecular equations, write net ionic equations and identify the Bronsted-Lowry acids and bases: a. \(2 \mathrm{HNO}_{3}(a q)+\mathrm{Ca}(\mathrm{OH})_{2}(a q) \rightarrow\) \(2 \mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}(a q)\) b. \(\mathrm{Na}_{2} \mathrm{CO}_{3}(a q)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow\) \(\mathrm{Na}_{2} \mathrm{SO}_{4}(a q)+\mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(\ell)\) c. \(\mathrm{CH}_{3} \mathrm{NH}_{2}(a q)+\mathrm{HBr}(a q) \rightarrow\left(\mathrm{CH}_{3} \mathrm{NH}_{3}\right) \mathrm{Br}(a q)\) d. \(2 \mathrm{CH}_{3} \mathrm{COOH}(a q)+\mathrm{Mg}(\mathrm{OH})_{2}(s) \rightarrow\) \(\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2} \mathrm{Mg}(a q)+2 \mathrm{H}_{2} \mathrm{O}(\ell)\) e. \(\mathrm{CaO}(s)+\mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow \mathrm{Ca}(\mathrm{OH})_{2}(s)\) f. \(\operatorname{LiH}(s)+\mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow \operatorname{LiOH}(a q)+\mathrm{H}_{2}(g)\) g. \(\mathrm{Ba}(\mathrm{OH})_{2}(a q)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow \mathrm{BaSO}_{4}(s)+2 \mathrm{H}_{2} \mathrm{O}(\ell)\) h. \(\mathrm{NaSH}(a q)+\mathrm{HNO}_{3}(a q) \rightarrow \mathrm{NaNO}_{3}(a q)+\mathrm{H}_{2} \mathrm{S}(g)\)

Write the chemical and the net ionic equations describing the reactions that occur when aqueous solutions of these pairs of compounds are mixed together. For each reaction label the Bronsted-Lowry acids and bases. a. HCl and \(\mathrm{Ca}(\mathrm{OH})_{2}\) b. \(\mathrm{H}_{3} \mathrm{PO}_{4}\) and \(\mathrm{KOH}\) c. HNO \(_{3}\) and \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) d. \(\mathrm{H}_{3} \mathrm{PO}_{4}\) and \(\mathrm{Ca}(\mathrm{OH})_{2}\)