Chapter 4

You choose to investigate some of the solubility guidelines for two ions not listed in Table $4.1,$ the chromate ion $\left({\mathrm{CrO}}_4^{2-}\right)$ and the oxalate ion $\left({\mathrm{C}}_2{\mathrm{O}}_4^{2-}\right).$ You are given $0.01\mathrm{M}$ solutions (A, B, C, D) of four water-soluble salts: $$\overline{)\begin{array}{lll}\text{ Solution }& \text{ Solute }& \text{ Color of Solution }\\ \text{ A }& {\mathrm{Na}}_2{\mathrm{CrO}}_4& \text{ Yellow }\\ \mathrm{B}& {\left({\mathrm{NH}}_4\right)}_2{\mathrm{C}}_2{\mathrm{O}}_4& \text{ Colorless }\\ \mathrm{C}& {\mathrm{AgNO}}_3& \text{ Colorless }\\ \mathrm{D}& {\mathrm{CaCl}}_2& \text{ Colorless }\end{array}}$$ When these solutions are mixed, the following observations are made: $$\overline{\begin{array}{lll}\text{ Expt }& \text{ Solutions }& \\ \text{ Number }& \text{ Mixed }& \text{ Result }\\ 1& \mathrm{A}+\mathrm{B}& \text{ No precipitate, yellow solution }\\ 2& \mathrm{A}+\mathrm{C}& \text{ Red precipitate forms }\\ 3& \mathrm{A}+\mathrm{D}& \text{ Yellow precipitate forms }\\ 4& \mathrm{B}+\mathrm{C}& \text{ White precipitate forms }\\ 5& \mathrm{B}+\mathrm{D}& \text{ White precipitate forms }\\ 6& \mathrm{C}+\mathrm{D}& \text{ White precipitate forms }\end{array}}$$ (a) Write a net ionic equation for the reaction that occurs in each of the experiments. (b) Identify the precipitate formed, if any, in each of the experiments.

Antacids are often used to relieve pain and promote healing in the treatment of mild ulcers. Write balanced net ionic equations for the reactions between the HCl(aq) in the stomach and each of the following substances used in various antacids: (a) $\mathrm{Al}(\mathrm{OH}{)}_3(s)$, (b) $\mathrm{Mg}(\mathrm{OH}{)}_2(s)$ (c) ${\mathrm{MgCO}}_3(s)$ (d) $\mathrm{NaAl}\left({\mathrm{CO}}_3\right)(\mathrm{OH}{)}_2(s),(\mathrm{e}){\mathrm{CaCO}}_3(s)$

The commercial production of nitric acid involves the following chemical reactions: $$\begin{array}{rl}4{\mathrm{NH}}_3(g)+5{\mathrm{O}}_2(g)& ⟶4\mathrm{NO}(g)+6{\mathrm{H}}_2\mathrm{O}(g)\\ 2\mathrm{NO}(g)+{\mathrm{O}}_2(g)& ⟶2{\mathrm{NO}}_2(g)\\ 3{\mathrm{NO}}_2(g)+{\mathrm{H}}_2\mathrm{O}(l)& ⟶2{\mathrm{HNO}}_3(aq)+\mathrm{NO}(g)\end{array}$$ (a) Which of these reactions are redox reactions? (b) In each redox reaction identify the element undergoing oxidation and the element undergoing reduction.

Consider the following reagents: zinc, copper, mercury (density $13.6\mathrm{g}/\mathrm{mL}$ ), silver nitrate solution, nitric acid solution. (a) Given a $500-\mathrm{mL}$ Erlenmeyer flask and a balloon can you combine two or more of the foregoing reagents to initiate a chemical reaction that will inflate the balloon? Write a balanced chemical equation to represent this process. What is the identity of the substance that inflates the balloon? (b) What is the theoretical yield of the substance that fills the balloon? (c) Can you combine two or more of the foregoing reagents to initiate a chemical reaction that will produce metallic silver? Write a balanced chemical equation to represent this process. What ions are left behind in solution? (d) What is the theoretical yield of silver?

Lanthanum metal forms cations with a charge of $3+.$ Consider the following observations about the chemistry of lanthanum: When lanthanum metal is exposed to air, a white solid (compound $\mathrm{A}$ ) is formed that contains lanthanum and one other element. When lanthanum metal is added to water, gas bubbles are observed and a different white solid (compound $\mathrm{B}$ ) is formed. Both $\mathrm{A}$ and $\mathrm{B}$ dissolve in hydrochloric acid to give a clear solution. When either of these solutions is evaporated, a soluble white solid (compound C) remains. If compound $\mathrm{C}$ is dissolved in water and sulfuric acid is added, a white precipitate (compound D) forms. (a) Propose identities for the substances $\mathrm{A},\mathrm{B},\mathrm{C},$ and $\mathrm{D}.(\mathbf{b})$ Write net ionic equations for all the reactions described. (c) Based on the preceding observations, what can be said about the position of lanthanum in the activity series (Table 4.5$)?$

A $35.0-\mathrm{mL}$ sample of $1.00\mathrm{M}\mathrm{KBr}$ and a $60.0-\mathrm{mL}$ sample of $0.600\mathrm{M}\mathrm{KBr}$ are mixed. The solution is then heated to evaporate water until the total volume is $50.0\mathrm{mL}$. What is the molarity of the KBr in the final solution?

Using modern analytical techniques, it is possible to detect sodium ions in concentrations as low as $50\mathrm{pg}/\mathrm{mL}$. What is this detection limit expressed in (a) molarity of ${\mathrm{Na}}^{+}$ (b) ${\mathrm{Na}}^{+}$ ions per cubic centimeter?

Hard water contains ${\mathrm{Ca}}^{2+},{\mathrm{Mg}}^{2+},$ and ${\mathrm{Fe}}^{2+},$ which interfere with the action of soap and leave an insoluble coating on the insides of containers and pipes when heated. Water softeners replace these ions with ${\mathrm{Na}}^{+}$. (a) If $1500\mathrm{L}$ of hard water contains $0.020\mathrm{M}{\mathrm{Ca}}^{2+}$ and $0.0040\mathrm{M}{\mathrm{Mg}}^{2+}$, how many moles of ${\mathrm{Na}}^{+}$ are needed to replace these ions? (b) If the sodium is added to the water softener in the form of $\mathrm{NaCl}$, how many grams of sodium chloride are needed?

Tartaric acid, ${\mathrm{H}}_2{\mathrm{C}}_4{\mathrm{H}}_4{\mathrm{O}}_6$, has two acidic hydrogens. The acid is often present in wines and precipitates from solution as the wine ages. A solution containing an unknown concentration of the acid is titrated with $\mathrm{NaOH}$. It requires $24.65\mathrm{mL}$ of $0.2500\mathrm{M}\mathrm{NaOH}$ solution to titrate both acidic protons in $50.00\mathrm{mL}$ of the tartaric acid solution. Write a balanced net ionic equation for the neutralization reaction, and calculate the molarity of the tartaric acid solution.

(a) A strontium hydroxide solution is prepared by dissolving $10.45\mathrm{g}$ of $\mathrm{Sr}(\mathrm{OH}{)}_2$ in water to make $50.00\mathrm{mL}$ of solution. What is the molarity of this solution? (b) Next the strontium hydroxide solution prepared in part (a) is used to titrate a nitric acid solution of unknown concentration. Write a balanced chemical equation to represent the reaction between strontium hydroxide and nitric acid solutions. (c) If $23.9\mathrm{mL}$ of the strontium hydroxide solution was needed to neutralize a $31.5\mathrm{mL}$ aliquot of the nitric acid solution, what is the concentration (molarity) of the acid?