Chapter 4

The concept of chemical equilibrium is very important. Which one of the following statements is the most correct way to think about equilibrium? (a) If a system is at equilibrium, nothing is happening. (b) If a system is at equilibrium, the rate of the forward reaction is equal to the rate of the back reaction. (c) If a system is at equilibrium, the product concentration is changing over time. Section 4.1\(]\)

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 \(\mathrm{Na}_{2} \mathrm{SO}_{4}\left(a_{4}\right)\) solution is added and a white precipitate forms. What is the identity of the unknown white solid? [Section 4.2\(]\)

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

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

An aqueous solution contains 1.2 \(\mathrm{mM}\) of total ions. (a) If the solution is NaCl(aq), what is the concentration of chloride ion? (b) If the solution is \(\mathrm{FeCl}_{3}(a q),\) what is the concentration of chloride ion? [Section 4.5\(]\)

State whether each of the following statements is true or false. Justify your answer in each case. \begin{equation} \begin{array}{l}{\text { (a) Electrolyte solutions conduct electricity because elec- }} \\ {\text { trons are moving through the solution. }} \\ {\text { (b) If you add a nonelectrolyte to an aqueous solution that }} \\ {\text { already contains an electrolyte, the electrical conduc- }} \\ {\text { tivity will not change. }}\end{array} \end{equation}

State whether each of the following statements is true or false. Justify your answer in each case. \begin{equation} \begin{array}{l}{\text { (a) When methanol, } \mathrm{CH}_{3} \mathrm{OH}, \text { is dissolved in water, a con- }} \\ {\text { ducting solution results. }} \\ {\text { (b) When acetic acid, } \mathrm{CH}_{3} \mathrm{COOH} \text { , dissolves in water, the }} \\ {\text { solution is weakly conducting and acidic in nature. }}\end{array} \end{equation}

We have learned in this chapter that many ionic solids dissolve in water as strong electrolytes; that is, as separated ions in solution. Which statement is most correct about this process? (a) Water is a strong acid and therefore is good at dissolving ionic solids. (b) Water is good at solvating ions because the hydrogen and oxygen atoms in water molecules bear partial charges. (c) The hydrogen and oxygen bonds of water are easily broken by ionic solids.

Would you expect that an anion would be physically closer to the oxygen or to the hydrogens of water molecules that surround it in solution?

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

Specify what ions are present upon dissolving each of the following substances in water: (a) \(\mathrm{MgI}_{2,}\) (b) \(\mathrm{K}_{2} \mathrm{CO}_{3,}$$(\mathbf{c})$$\mathrm{HClO}_{4,}\) \((\mathbf{d}) \mathrm{NaCH}_{3} \mathrm{COO.}\)

Formic acid, HCOOH, is a weak electrolyte. What solutes are present in an aqueous solution of this compound? Write the chemical equation for the ionization of HCOOH.

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

Predict whether each of the following compounds is soluble in water: \((\mathbf{a})\mathrm{AgI},(\mathbf{b}) \mathrm{Na}_{2} \mathrm{CO}_{3},(\mathbf{c}) \mathrm{BaCl}_{2},(\mathbf{d}) \mathrm{Al}(\mathrm{OH})_{3}$$(\mathbf{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 reaction. (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 \(\mathrm{HCl},\) (b) \(\mathrm{KOH}\) and \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2},(\mathbf{c}) \mathrm{Na}_{2} \mathrm{S}\) and \(\mathrm{CdSO}_{4}\) .

Which ions remain in solution, unreacted, after each of the following pairs of solutions is mixed? \begin{equation} \begin{array}{l}{\text { (a) potassium carbonate and magnesium sulfate }} \\\ {\text { (b) lead nitrate and lithium sulfide }} \\ {\text { (c) ammonium phosphate and calcium chloride }}\end{array} \end{equation}

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) \(\operatorname{Ba}\left(\mathrm{NO}_{3}\right)_{2}(a q)+\mathrm{K}_{2} \mathrm{SO}_{4}(a q) \longrightarrow\) (c) \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}(a q)+\mathrm{KOH}(a q) \longrightarrow\)

Separate samples of a solution of an unknown salt are treated with dilute solutions of \(\mathrm{HBr}, \mathrm{H}_{2} \mathrm{SO}_{4},\) and \(\mathrm{NaOH} .\) A precipitate forms in all three cases. Which of the following cations could be present in the unknown salt solution: \(\mathrm{K}^{+}, \mathrm{Pb}^{2+}, \mathrm{Ba}^{2+}.\)

You know that an unlabeled bottle contains an aqueous solution of one of the following: \(A g N O_{3},\) CaCl \(_{2},\) or \(A l_{2}\left(S O_{4}\right)_{3}\) . A friend suggests that you test a portion of the solution with \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\) and then with NaCl solutions. According to your friend's logic, which of these chemical reactions could occur, thus helping you identify the solution in the bottle? (a) Barium sulfate could precipitate. (b) Silver chloride could precipitate. (c) silver sulfate could precipitate. (d) More than one, but not all, of the reactions described in answers a-c could occur. (e) All three reactions described in answers a-c could occur.

State whether each of the following statements is true or false. Justify your answer in each case. \begin{equation} \begin{array}{l}{\text { (a) Sulfuric acid is a monoprotic acid. }} \\ {\text { (b) HCl is a weak acid. }} \\ {\text { (c) Methanol is a base. }}\end{array} \end{equation}

State whether each of the following statements is true or false. Justify your answer in each case. (a) \(\mathrm{NH}_{3}\) contains no \(\mathrm{OH}^{-}\) ions, and yet its aqueous solutions are basic. (b) HF is a strong acid. (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,\(\mathrm{CH}_{3} \mathrm{CN},(\mathbf{c}) \mathrm{NaClO}_{4},(\mathbf{d}) \mathrm{Ba}(\mathrm{OH})_{2} .\)

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 NaCl of the same concentration. Which of the following substances could the unknown be: 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) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) (ethanol), \((\mathbf{c}) \mathrm{NH}_{3},(\mathbf{d}) \mathrm{KClO}_{3}\), \((\mathbf{e}) \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\).

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), \((\mathbf{d}) \mathrm{HClO}_{3}\) (e) \(\mathrm{CuSO}_{4}\), \((\mathbf{f}) \mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\) (sucrose).

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

Write the balanced molecular and net ionic equations for each of the following neutralization reactions: \begin{equation} \begin{array}{l}{\text { (a) Aqueous acetic acid is neutralized by aqueous barium }} \\ {\text { hydroxide. }} \\ {\text { (b) Solid chromium(II) hydroxide reacts with nitrous acid. }} \\ {\text { (c) Aqueous nitric acid and aqueous ammonia react. }}\end{array} \end{equation}

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 netionic equation for the reaction that occurs when each substance reacts with a hydrochloric acid solution. (b) By observing the reactions in part (a), how could you distinguish any of the three magnesium substances from the other two?

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

True or false: \begin{equation} \begin{array}{l}{\text { (a) If a substance is oxidized, it is gaining electrons. }} \\ {\text { (b) If an ion is oxidized, its oxidation number increases. }}\end{array} \end{equation}

True or false: \begin{equation} \begin{array}{l}{\text { (a) Oxidation can occur without oxygen. }} \\ {\text { (b) Oxidation can occur without reduction. }}\end{array} \end{equation}

Determine the oxidation number of sulfur in each of the following substances: (a) barium sulfate, \(\mathrm{BaSO}_{4}\) (b) sulfurous acid, \(\mathrm{H}_{2} \mathrm{SO}_{3},(\mathbf{c})\) strontium sulfide, \(\mathrm{SrS},(\mathbf{d})\) hydrogen sulfide, \(\mathrm{H}_{2} \mathrm{S} .\) (e) Locate sulfur in the periodic table in Exercise 4.47; what region is it in? (f) Which region(s) of the periodic table contains elements that can adopt both positive and negative oxidation numbers?

Determine the oxidation number for the indicated element in each of the following substances: (a) \(\sin \mathrm{SO}_{2},(\mathbf{b}) \mathrm{Cin} \mathrm{COCl}_{2}\) , (c) \(\mathrm{Mn}\) in \(\mathrm{KMnO}_{4},(\mathbf{d}) \mathrm{Brin} \mathrm{HBrO},(\mathbf{e}) \mathrm{P}\) in \(\mathrm{PF}_{3},(\mathbf{f}) \mathrm{O}\) in \(\mathrm{K}_{2} \mathrm{O}_{2}\)

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

Which element is oxidized, and which is reduced in the following reactions? \begin{equation} \begin{array}{l}{\text { (a) } \mathrm{N}_{2}(g)+3 \mathrm{H}_{2}(g) \longrightarrow 2 \mathrm{NH}_{3}(g)\longrightarrow} \\ {\text { (b) } 3 \mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}(a q)+2 \mathrm{Al}(s) \longrightarrow} \\\\\quad \quad\quad\quad\quad\quad\quad\quad\quad\quad\quad{3 \mathrm{Fe}(s)+2 \mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}(a q)}\\\\{\text { (c) } \mathrm{Cl}_{2}(a q)+2 \operatorname{Nal}(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} \end{equation}

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.\begin{equation} \begin{array}{c}{\text { (a) } \mathrm{P}_{4}(s)+10 \mathrm{HClO}(a q)+6 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow} \\\ \quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad{\quad 4 \mathrm{H}_{3} \mathrm{PO}_{4}(a q)+10 \mathrm{HCl}(a q)}\end{array} \end{equation} \begin{equation} \begin{array}{l}\quad\quad\quad\quad\quad\quad{\text { (b) } \mathrm{Br}_{2}(l)+2 \mathrm{K}(s) \longrightarrow 2 \mathrm{KBr}(s)} \\\\\quad\quad\quad\quad\quad\quad {\text { (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)}\end{array} \end{equation} \begin{equation} \begin{array}{r}\quad\quad\quad\quad{\text { (d) } \mathrm{ZnCl}_{2}(a q)+2 \mathrm{NaOH}(a q) \longrightarrow \mathrm{Zn}(\mathrm{OH})_{2}(s)+} \\ {2 \mathrm{NaCl}(a q)}\end{array} \end{equation}

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, 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, write \(\mathrm{NR}\) . (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 \(\mathrm{Cd}^{2+}\) 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) Which elements more closely define 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?

The following reactions (note that the arrows are pointing only one direction) can be used to prepare an activity series for the halogens: $$\begin{array}{c}{\mathrm{Br}_{2}(a q)+2 \mathrm{Nal}(a q) \longrightarrow 2 \mathrm{NaBr}(a q)+\mathrm{I}_{2}(a q)} \\ {\mathrm{Cl}_{2}(a q)+2 \mathrm{NaBr}(a q) \longrightarrow 2 \mathrm{NaCl}(a q)+\mathrm{Br}_{2}(a q)}\end{array}$$ (a) Which elemental halogen would you predict is the most stable, upon mixing with other halides? (b) Predict whether a reaction will occur when elemental chlorine and potassium iodide are mixed. (c) Predict whether a reaction will occur when elemental bromine and lithium chloride are mixed.

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

You make 1.000 L of an aqueous solution that contains 35.0 \(\mathrm{g}\) of sucrose \(\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right) .\) (a) What is the molarity of sucrose in this solution? (b) How many liters of water would you have to add to this solution to reduce the molarity you calculated in part (a) by a factor of two?

(a) Calculate the molarity of a solution that contains 0.175 mol \(Z \mathrm{nCl}_{2}\) in exactly 150 \(\mathrm{mL}\) of solution. (b) How many moles of protons are present in 35.0 \(\mathrm{mL}\) of a 4.50 \(\mathrm{M}\) solution of nitric acid? (c) How many milliliters of a 6.00\(M\) NaOH solution are needed to provide 0.350 mol of \(\mathrm{NaOH}\) ?

(a) Calculate the molarity of a solution made by dissolving 12.5 grams of \(\mathrm{Na}_{2} \mathrm{CrO}_{4}\) in enough water to form exactly 750 \(\mathrm{mL}\) of solution. (b) How many moles of KBr are present in 150 \(\mathrm{mL}\) of a 0.112\(M\) solution? (c) How many milliliters of 6.1\(M \mathrm{HCl}\) solution are needed to obtain 0.150 \(\mathrm{mol}\) of \(\mathrm{HCl}\) ?

The average adult human male has a total blood volume of 5.0 L. If the concentration of sodium ion in this average individual is \(0.135 \mathrm{M},\) what is the mass of sodium ion circulating in the blood?