Chapter 4

You are presented with a white solid and told that due to careless labeling it is not clear if the substance is barium chloride, lead chloride, or zinc chloride. When you transfer the solid to a beaker and add water, the solid dissolves to give a clear solution. Next a \(\mathrm{Na}_{2} \mathrm{SO}_{4}(a q)\) solution is added and a white precipitate forms. What is the identity of the unknown white solid? \([\) Section 4.2\(]\)

We have seen that ions in aqueous solution are stabilized by the attractions between the ions and the water molecules. Why then do some pairs of ions in solution form precipitates? \([\) Section 4.2\(]\)

Which of the following ions will always be a spectator ion in a precipitation reaction? (a) \(\mathrm{Cl}^{-},(\mathrm{b}) \mathrm{NO}_{3}^{-},(\mathrm{c}) \mathrm{NH}_{4}^{+},(\mathrm{d}) \mathrm{S}^{2-},\) (e) \(\mathrm{SO}_{4}^{2-}\). Explain briefly. [Section \(\left.4.2\right]\)

The labels have fallen off three bottles containing powdered samples of metals; one contains zinc, one lead, and the other platinum. You have three solutions at your disposal: \(1 \mathrm{M}\) sodium nitrate, \(1 \mathrm{M}\) nitric acid, and \(1 \mathrm{M}\) nickel nitrate. How could you use these solutions to determine the identities of each metal powder? [Section 4.4]

Explain how a redox reaction involves electrons in the same way that a neutralization reaction involves protons. [Sections 4.3 and 4.4\(]\)

If you want to double the concentration of a solution, how could you do it? [Section 4.5\(]\)

When methanol, \(\mathrm{CH}_{3} \mathrm{OH},\) is dissolved in water, a nonconducting solution results. When acetic acid, \(\mathrm{CH}_{3} \mathrm{COOH},\) dissolves in water, the solution is weakly conducting and acidic in nature. Describe what happens upon dissolution in the two cases, and account for the different results.

We have learned in this chapter that many ionic solids dissolve in water as strong electrolytes, that is, as separated ions in solution. What properties of water facilitate this process? Would you expect ionic compounds to be soluble in elemental liquids like bromine or mercury, just as they are in water? Explain.

What does it mean to say that ions are solvated when an ionic substance dissolves in water?

Specify what ions are present in solution upon dissolving each of the following substances in water: (a) \(\mathrm{ZnCl}_{2}\), (b) \(\mathrm{HNO}_{3}\), (c) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\) (d) \(\mathrm{Ca}(\mathrm{OH})_{2}\)

Specify what ions are present upon dissolving each of the following substances in water: (a) \(\mathrm{MgI}_{2}\), (b) \(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3},\) (c) \(\mathrm{HClO}_{4}\), (d) \(\mathrm{NaCH}_{3} \mathrm{COO}\)

Formic acid, \(\mathrm{HCOOH},\) is a weak electrolyte. What solute particles are present in an aqueous solution of this compound? Write the chemical equation for the ionization of \(\mathrm{HCOOH}\).

Acetone, \(\mathrm{CH}_{3} \mathrm{COCH}_{3},\) is a nonelectrolyte; hypochlorous acid, \(\mathrm{HClO},\) is a weak electrolyte; and ammonium chloride, \(\mathrm{NH}_{4} \mathrm{Cl},\) is a strong electrolyte. (a) What are the solute particles present in aqueous solutions of each compound? (b) If \(0.1 \mathrm{~mol}\) of each compound is dissolved in solution, which one contains \(0.2 \mathrm{~mol}\) of solute particles, which contains \(0.1 \mathrm{~mol}\) of solute particles, and which contains somewhere between 0.1 and 0.2 mol of solute particles?

Using solubility guidelines, predict whether each of the following compounds is soluble or insoluble in water: (a) \(\mathrm{MgBr}_{2}\), (b) \(\mathrm{PbI}_{2}\), (c) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{CO}_{3}\) (e) \(\mathrm{ZnSO}_{4}\). (d) \(\mathrm{Sr}(\mathrm{OH})_{2}\),

Predict whether each of the following compounds is soluble in water: (a) \(\mathrm{AgI},\) (b) \(\mathrm{Na}_{2} \mathrm{CO}_{3},\) (c) \(\mathrm{BaCl}_{2},\) (d) \(\mathrm{Al}(\mathrm{OH})_{3}\), (e) \(\mathrm{Zn}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}\).

Will precipitation occur when the following solutions are mixed? If so, write a balanced chemical equation for the reac- tion. (a) \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) and \(\mathrm{AgNO}_{3},\) (b) \(\mathrm{NaNO}_{3}\) and \(\mathrm{NiSO}_{4}\), (c) \(\mathrm{FeSO}_{4}\) and \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}\).

Identify the precipitate (if any) that forms when the following solutions are mixed, and write a balanced equation for each reaction. (a) \(\mathrm{NaCH}_{3} \mathrm{COO}\) and \(\mathrm{HCl},(\mathrm{b}) \mathrm{KOH}\) and \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\), (c) \(\mathrm{Na}_{2} \mathrm{~S}\) and \(\mathrm{CdSO}_{4}\).

Name the spectator ions in any reactions that may be involved when each of the following pairs of solutions are mixed. (a) \(\mathrm{Na}_{2} \mathrm{CO}_{3}(a q)\) and \(\mathrm{MgSO}_{4}(a q)\) (b) \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(a q)\) and \(\mathrm{Na}_{2} \mathrm{~S}(a q)\) (c) \(\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4}(a q)\) and \(\mathrm{CaCl}_{2}(a q)\)

Write balanced net ionic equations for the reactions that occur in each of the following cases. Identify the spectator ion or ions in each reaction. (a) \(\mathrm{Cr}_{2}\left(\mathrm{SO}_{4}\right)_{3}(a q)+\left(\mathrm{NH}_{4}\right)_{2} \mathrm{CO}_{3}(a q) \longrightarrow\) (b) \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}(a q)+\mathrm{K}_{2} \mathrm{SO}_{4}(a q) \longrightarrow\) (c) \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}(a q)+\mathrm{KOH}(a q) \longrightarrow\).

Separate samples of a solution of an unknown ionic compound are treated with dilute \(\mathrm{AgNO}_{3}, \mathrm{~Pb}\left(\mathrm{NO}_{3}\right)_{2},\) and \(\mathrm{BaCl}_{2}\). Precipitates form in all three cases. Which of the following could be the anion of the unknown salt: \(\mathrm{Br}^{-}, \mathrm{CO}_{3}^{2-}, \mathrm{NO}_{3}^{-}\) ?

You know that an unlabeled bottle contains a solution of one of the following: \(\mathrm{AgNO}_{3}, \mathrm{CaCl}_{2}\), or \(\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3} .\) A friend suggests that you test a portion of the solution with \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\) and then with \(\mathrm{NaCl}\) solutions. Explain how these two tests together would be sufficient to determine which salt is present in the solution.

Three solutions are mixed together to form a single solution. One contains \(0.2 \mathrm{~mol} \mathrm{~Pb}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2},\) the second contains \(0.1 \mathrm{~mol} \mathrm{Na}_{2} \mathrm{~S},\) and the third contains \(0.1 \mathrm{~mol} \mathrm{CaCl}_{2}\). (a) Write the net ionic equations for the precipitation reaction or reactions that occur. (b) What are the spectator ions in the solution?

What is the difference between (a) a monoprotic acid and a diprotic acid, \((\mathbf{b})\) a weak acid and a strong acid, \((\mathbf{c})\) an acid and a base?

Explain the following observations: (a) \(\mathrm{NH}_{3}\) contains no \(\mathrm{OH}^{-}\) ions, and yet its aqueous solutions are basic; (b) HF is called a weak acid, and yet it is very reactive; (c) although sulfuric acid is a strong electrolyte, an aqueous solution of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) contains more \(\mathrm{HSO}_{4}^{-}\) ions than \(\mathrm{SO}_{4}^{2-}\) ions.

Explain the following observations: (a) \(\mathrm{NH}_{3}\) contains no \(\mathrm{OH}^{-}\) ions, and yet its aqueous solutions are basic; (b) HF is called a weak acid, and yet it is very reactive; (c) although sulfuric acid is a strong electrolyte, an aqueous solution of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) contains more \(\mathrm{HSO}_{4}^{-}\) ions than \(\mathrm{SO}_{4}^{2-}\) ions.

Label each of the following substances as an acid, base, salt, or none of the above. Indicate whether the substance exists in aqueous solution entirely in molecular form, entirely as ions, or as a mixture of molecules and ions. (a) HF, (b) acetonitrile, \(\mathrm{CH}_{3} \mathrm{CN},\) (c) \(\mathrm{NaClO}_{4},\) (d) \(\mathrm{Ba}(\mathrm{OH})_{2}\).

An aqueous solution of an unknown solute is tested with litmus paper and found to be acidic. The solution is weakly conducting compared with a solution of \(\mathrm{NaCl}\) of the same concentration.Which of the following substances could the unknown be: \(\mathrm{KOH}, \mathrm{NH}_{3}, \mathrm{HNO}_{3}, \mathrm{KClO}_{2}, \mathrm{H}_{3} \mathrm{PO}_{3}, \mathrm{CH}_{3} \mathrm{COCH}_{3}\) (acetone)?

Classify each of the following substances as a nonelectrolyte, weak electrolyte, or strong electrolyte in water: (a) \(\mathrm{H}_{2} \mathrm{SO}_{3}\), (b) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\) (ethanol), (c) \(\mathrm{NH}_{3}\), (d) \(\mathrm{KClO}_{3}\), (e) \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\)

Classify each of the following aqueous solutions as a nonelectrolyte, weak electrolyte, or strong electrolyte: (a) \(\mathrm{LiClO}_{4}\), (b) \(\mathrm{HClO}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) (propanol), (d) \(\mathrm{HClO}_{3}\), (e) \(\mathrm{CuSO}_{4}\), (f) \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\) (sucrose).

Complete and balance the following molecular equations, and then write the net ionic equation for each: (a) \(\mathrm{HBr}(a q)+\mathrm{Ca}(\mathrm{OH})_{2}(a q) \longrightarrow\) (b) \(\mathrm{Cu}(\mathrm{OH})_{2}(s)+\mathrm{HClO}_{4}(a q) \longrightarrow\) (c) \(\mathrm{Al}(\mathrm{OH})_{3}(s)+\mathrm{HNO}_{3}(a q) \longrightarrow\)

Write the balanced molecular and net ionic equations for each of the following neutralization reactions: (a) Aqueous acetic acid is neutralized by aqueous barium hydroxide. (b) Solid chromium(III) hydroxide reacts with nitrous acid. (c) Aqueous nitric acid and aqueous ammonia react.

Write balanced molecular and net ionic equations for the following reactions, and identify the gas formed in each: (a) solid cadmium sulfide reacts with an aqueous solution of sulfuric acid; (b) solid magnesium carbonate reacts with an aqueous solution of perchloric acid.

Because the oxide ion is basic, metal oxides react readily with acids. (a) Write the net ionic equation for the following reaction: \(\mathrm{FeO}(s)+2 \mathrm{HClO}_{4}(a q) \longrightarrow \mathrm{Fe}\left(\mathrm{ClO}_{4}\right)_{2}(a q)+\mathrm{H}_{2} \mathrm{O}(l)\) (b) Based on the equation in part (a), write the net ionic equation for the reaction that occurs between \(\mathrm{NiO}(s)\) and an aqueous solution of nitric acid.

Magnesium carbonate, magnesium oxide, and magnesium hydroxide are all white solids that react with acidic solutions. (a) Write a balanced molecular equation and a net ionic equation for the reaction that occurs when each substance reacts with a hydrochloric acid solution. (b) By observing the reactions in part (a) could you distinguish any of the three magnesium substances from the other two? If so how? (c) If excess \(\mathrm{HCl}(a q)\) is added, would the clear solutions left behind after the reaction is complete contain the same or different ions in each case?

As \(\mathrm{K}_{2} \mathrm{O}\) dissolves in water, the oxide ion reacts with water molecules to form hydroxide ions. Write the molecular and net ionic equations for this reaction. Based on the definitions of acid and base, what ion is the base in this reaction? What is the acid? What is the spectator ion in the reaction?

Define oxidation and reduction in terms of (a) electron transfer and (b) oxidation numbers.

Can oxidation occur without oxygen? Can oxidation occur without reduction?

Determine the oxidation number of sulfur in each of the following substances: (a) barium sulfate, \(\mathrm{BaSO}_{4},\) (b) sulfurous acid, \(\mathrm{H}_{2} \mathrm{SO}_{3},\) (c) strontium sulfide, \(\mathrm{SrS},\) (d) hydrogen sulfide, \(\mathrm{H}_{2} \mathrm{~S} .\) (e) Based on these compounds what is the range of oxidation numbers seen for sulfur? Is there any relationship between the range of accessible oxidation states and sulfur's position on the periodic table?

Determine the oxidation number for the indicated element in each of the following substances: (a) \(\mathrm{S}\) in \(\mathrm{SO}_{2},\) (b) \(\mathrm{C}\) in \(\mathrm{COCl}_{2}\), (c) \(\mathrm{Mn}\) in \(\mathrm{KMnO}_{4}\) (d) \(\mathrm{Br}\) in \(\mathrm{HBrO}\) (e) As in As \(_{4}\), (f) \(\mathrm{O}\) in \(\mathrm{K}_{2} \mathrm{O}_{2}\)

Determine the oxidation number for the indicated element (b) \(\mathrm{Al}\) in each of the following compounds: (a) \(\mathrm{Co}\) in \(\mathrm{LiCoO}_{2}\), in \(\mathrm{NaAlH}_{4}\), (c) \(\mathrm{C}\) in \(\mathrm{CH}_{3} \mathrm{OH}\) (methanol), \((\mathrm{d}) \mathrm{N}\) in \(\mathrm{GaN},\) (e) Cl in \(\mathrm{HClO}_{2},\) (f) \(\mathrm{Cr}\) in \(\mathrm{BaCrO}_{4}\)

Which element is oxidized and which is reduced in the follow- ing reactions? $$ \begin{array}{l} \text { (a) } \mathrm{N}_{2}(g)+3 \mathrm{H}_{2}(g) \longrightarrow 2 \mathrm{NH}_{3}(g) \\ \text { (b) } 3 \mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}(a q)+2 \mathrm{Al}(s) \longrightarrow \\ \text { (c) } \mathrm{Cl}_{2}(a q)+2 \mathrm{NaI}(a q) \longrightarrow \mathrm{I}_{2}(a q)+2 \mathrm{NaCl}(a q) \\ \text { (d) } \mathrm{PbS}(s)+4 \mathrm{H}_{2} \mathrm{O}_{2}(a q) \longrightarrow \mathrm{PbSO}_{4}(s)+4 \mathrm{H}_{2} \mathrm{O}(l) \end{array} $$

Which of the following are redox reactions? For those that are, indicate which element is oxidized and which is reduced. For those that are not, indicate whether they are precipitation or neutralization reactions. (a) \(\mathrm{P}_{4}(s)+10 \mathrm{HClO}(a q)+6 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow\) $$ 4 \mathrm{H}_{3} \mathrm{PO}_{4}(a q)+10 \mathrm{HCl}(a q) $$ (b) \(\mathrm{Br}_{2}(l)+2 \mathrm{~K}(\mathrm{~s}) \longrightarrow 2 \mathrm{KBr}(s)\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}(l)+3 \mathrm{O}_{2}(g) \longrightarrow 3 \mathrm{H}_{2} \mathrm{O}(l)+2 \mathrm{CO}_{2}(g)\) (d) \(\mathrm{ZnCl}_{2}(a q)+2 \mathrm{NaOH}(a q) \longrightarrow \mathrm{Zn}(\mathrm{OH})_{2}(s)+2 \mathrm{NaCl}(a q)\)

Write balanced molecular and net ionic equations for the reactions of (a) manganese with dilute sulfuric acid, (b) chromium with hydrobromic acid, (c) tin with hydrochloric acid, (d) aluminum with formic acid, HCOOH.

Write balanced molecular and net ionic equations for the reactions of (a) hydrochloric acid with nickel, (b) dilute sulfuric acid with iron, (c) hydrobromic acid with magnesium, (d) acetic acid, \(\mathrm{CH}_{3} \mathrm{COOH},\) with zinc.

Using the activity series (Table 4.5 ), write balanced chemical equations for the following reactions. If no reaction occurs, simply write NR. (a) Iron metal is added to a solution of copper(II) nitrate; (b) zinc metal is added to a solution of magnesium sulfate; (c) hydrobromic acid is added to tin metal; (d) hydrogen gas is bubbled through an aqueous solution of nickel(II) chloride; (e) aluminum metal is added to a solution of cobalt(II) sulfate.

Using the activity series (Table 4.5 ), write balanced chemical equations for the following reactions. If no reaction occurs, simply write NR. (a) Nickel metal is added to a solution of copper(II) nitrate; (b) a solution of zinc nitrate is added to a solution of magnesium sulfate; (c) hydrochloric acid is added to gold metal; (d) chromium metal is immersed in an aqueous solution of cobalt(II) chloride; (e) hydrogen gas is bubbled through a solution of silver nitrate.

The metal cadmium tends to form Cd \(^{2+}\) ions. The following observations are made: (i) When a strip of zinc metal is placed in \(\mathrm{CdCl}_{2}(a q),\) cadmium metal is deposited on the strip. (ii) When a strip of cadmium metal is placed in \(\mathrm{Ni}\left(\mathrm{NO}_{3}\right)_{2}(a q),\) nickel metal is deposited on the strip. (a) Write net ionic equations to explain each of the preceding observations. (b) What can you conclude about the position of cadmium in the activity series? (c) What experiments would you need to perform to locate more precisely the position of cadmium in the activity series?

(a) Use the following reactions to prepare an activity series for the halogens: $$ \begin{aligned} \mathrm{Br}_{2}(a q)+2 \mathrm{NaI}(a q) & \longrightarrow 2 \mathrm{NaBr}(a q)+\mathrm{I}_{2}(a q) \\ \mathrm{Cl}_{2}(a q)+2 \mathrm{NaBr}(a q) & \longrightarrow 2 \mathrm{NaCl}(a q)+\mathrm{Br}_{2}(a q) \end{aligned} $$ (b) Relate the positions of the halogens in the periodic table with their locations in this activity series. (c) Predict whether a reaction occurs when the following reagents are mixed: \(\mathrm{Cl}_{2}(a q)\) and \(\mathrm{KI}(a q) ; \operatorname{Br}_{2}(a q)\) and \(\operatorname{LiCl}(a q)\)

(a) Is the concentration of a solution an intensive or an extensive property? (b) What is the difference between \(0.50 \mathrm{~mol}\) \(\mathrm{HCl}\) and \(0.50 \mathrm{M} \mathrm{HCl} ?\)

(a) Suppose you prepare \(500 \mathrm{~mL}\) of a \(0.10 \mathrm{M}\) solution of some salt and then spill some of it. What happens to the concentration of the solution left in the container? (b) Suppose you prepare \(500 \mathrm{~mL}\) of a \(0.10 \mathrm{M}\) aqueous solution of some salt and let it sit out, uncovered, for a long time, and some water evaporates. What happens to the concentration of the solution left in the container? (c) A certain volume of a \(0.50 \mathrm{M}\) solution contains \(4.5 \mathrm{~g}\) of a salt. What mass of the salt is present in the same volume of a \(2.50 \mathrm{M}\) solution?