Chapter 1

If solutions of iron (III) nitrate and sodium carbonate are mixed, what would be the formula of the precipitate? (A) \(\mathrm{Fe} 3 \mathrm{CO}_{3}\) (B) \(\mathrm{Fe}_{2}\left(\mathrm{CO}_{3}\right)_{3}\) (C) \(\mathrm{NaNO}_{3}\) (D) No precipitate would form.

Directions: Questions 1-3 are long free-response questions that require about 23 minutes each to answer and are worth 10 points each. Write your response in the space provided following each question. Examples and equations may be included in your responses where appropriate. For calculations, clearly show the method used and the steps involved in arriving at your answers. You must show your work to receive credit for your answer. Pay attention to significant figures. A student is tasked with determining the identity of an unknown carbonate compound with a mass of 1.89 g. The compound is first placed in water, where it dissolves completely. The \(K_{s p}\) value for several carbonate-containing compounds are given below. $$\begin{array}{|c|c|}\hline \text { Compound } & {K_{s p}} \\ \hline \text { Lithium carbonate } & {8.15 \times 10^{-4}} \\ \hline \text { Nickel (II) carbonate } & {1.42 \times 10^{-7}} \\ \hline \text { Strontium carbonate } & {5.60 \times 10^{-10}} \\ \hline\end{array}$$ (a) In order to precipitate the maximum amount of the carbonate ions from solution, which of the following should be added to the carbonate solution: \(\operatorname{LiNO}_{3}, \mathrm{Ni}\left(\mathrm{NO}_{3}\right)_{2},\) or \(\mathrm{Sr}\left(\mathrm{NO}_{3}\right)_{2} ?\) Justify your answer. (b) For the carbonate compound that contains the cation chosen in part (a), determine the concentration of each ion of that compound in solution at equilibrium. (c) When mixing the solution, should the student ensure the carbonate solution or the nitrate solution is in excess? Justify your answer. (d) After titrating sufficient solution to precipitate out all of the carbonate ions, the student filters the solution before placing it in a crucible and heating it to drive off the water. After several heatings, the final mass of the precipitate remains constant and is determined to be 2.02 g. (i) Determine the number of moles of precipitate. (ii) Determine the mass of carbonate present in the precipitate. (e) Determine the percent, by mass, of carbonate in the original sample. (f) Is the original compound most likely lithium carbonate, sodium carbonate, or potassium carbonate? Justify your answer.

In a saturated solution of \(\mathrm{Na}_{3} \mathrm{PO}_{4},\left[\mathrm{Na}^{+}\right]=0.30 \mathrm{M} .\) What is the molar solubility of \(\mathrm{Na}_{3} \mathrm{PO}_{4} ?\)

A multi-step reaction takes place with the following elementary steps: $\begin{array}{ll}{\text { Step I. }} & {A+B=C} \\ {\text { Step II. }} & {C+A \rightarrow D} \\ {\text { Step III. }} & {C+D \rightarrow B+E}\end{array}$ What is the overall balanced equation for this reaction? (A) 2A + B + 2C + D ? C + D + B + E (B) A + B ? B + E (C) A + 2C ? D + E (D) 2A + C ? E

Why does \(\mathrm{CaF}_{2}\) have a higher melting point than \(\mathrm{NH}_{3} ?\) (A) \(\mathrm{CaF}_{2}\) is more massive and thus has stronger London dispersion forces. (B) CaF_2 exhibits network covalent bonding, which is the strongest type of bonding. (C) CaF_2 is smaller and exhibits greater Coulombic attractive forces. (D) \(\mathrm{CaF}_{2}\) is an ionic substance and it requires a lot of energy to break up an ionic lattice.

Use the following information to answer questions 1-5. \(\begin{array}{ll}{\text { Reaction } 1 : \mathrm{N}_{2} \mathrm{H}_{4}(l)+\mathrm{H}_{2}(g) \rightarrow 2 \mathrm{NH}_{3}(g)} & {\Delta H=?} \\ {\text { Reaction } 2 : \mathrm{N}_{2} \mathrm{H}_{4}(l)+\mathrm{CH}_{4} \mathrm{O}(l) \rightarrow \mathrm{CH}_{2} \mathrm{O}(g)+\mathrm{N}_{2}(g)+3 \mathrm{H}_{2}(g)} & {\Delta H=-37 \mathrm{kJ} / \mathrm{mol}_{\mathrm{rxn}}} \\ {\text { Reaction } 3 : \mathrm{N}_{2}(g)+3 \mathrm{H}_{2}(g) \rightarrow 2 \mathrm{NH}_{3}(g)} & {\Delta H=-46 \mathrm{kJ} / \mathrm{mol}_{\mathrm{rxn}}} \\ {\text { Reaction } 4 : \mathrm{CH}_{4} \mathrm{O}(l) \rightarrow \mathrm{CH}_{2} \mathrm{O}(g)+\mathrm{H}_{2}(g)} & {\Delta H=-65 \mathrm{kJ} / \mathrm{mol}_{\mathrm{rxn}}}\end{array}\) What is the enthalpy change for reaction 1\(?\) (A) \(-148 \mathrm{kJ} / \mathrm{mol}_{\mathrm{rxn}}\) (B) \(-56 \mathrm{kJ} / \mathrm{mol}_{\mathrm{rxn}}\) (C) \(-18 \mathrm{kJ} / \mathrm{mol}_{\mathrm{rxn}}\) (D) \(+148 \mathrm{kJ} / \mathrm{mol}_{\mathrm{rxn}}\)

A student titrates 20.0 \(\mathrm{mL}\) of 1.0 \(M \mathrm{NaOH}\) with 2.0 \(\mathrm{M}\), \(\mathrm{HCO}_{2} \mathrm{H}\left(K_{\mathrm{a}}=1.8 \times 10^{-4}\right) .\) Formic acid is a monoprotic acid. How much formic acid is necessary to reach the equivalence point? (A) 10.0 mL (B) 20.0 mL (C) 30.0 mL (D) 40.0 mL

If solutions containing equal amounts of \(\mathrm{AgNO}_{3}\) and \(\mathrm{KCl}\) are mixed, what is the identity of the spectator ions? (A) \(\mathrm{Ag}^{+}, \mathrm{NO}_{3}^{-}, \mathrm{K}^{+},\) and \(\mathrm{Cl}^{-}\) (B) \(\mathrm{Ag}^{+}\) and \(\mathrm{Cl}^{-}\) (C) \(\mathrm{K}^{+}\) and \(\mathrm{Ag}^{+}\) (D) \(\mathrm{K}^{+}\) and \(\mathrm{NO}_{3}^{-}\)

Directions: Questions 1-3 are long free-response questions that require about 23 minutes each to answer and are worth 10 points each. Write your response in the space provided following each question. Examples and equations may be included in your responses where appropriate. For calculations, clearly show the method used and the steps involved in arriving at your answers. You must show your work to receive credit for your answer. Pay attention to significant figures. The unbalanced reaction between potassium permanganate and acidified iron (II) sulfate is a redox reaction that proceeds as follows: $$\mathrm{H}^{+}(a q)+\mathrm{Fe}^{2+}(a q)+\mathrm{MnO}_{4}^{-(a q)} \rightarrow \mathrm{Mn}^{2+}(a q)+\mathrm{Fe}^{3+}(a q)+\mathrm{H}_{2} \mathrm{O}(l)$$ (a) Provide the equations for both half-reactions that occur below: (i) Oxidation half-reaction (ii) Reduction half-reaction (b) What is the balanced net ionic equation? A solution of 0.150 M potassium permanganate is placed in a buret before being titrated into a flask containing 50.00 mL of iron (II) sulfate solution of unknown concentration. The following data describes the colors of the various ions in solution: $$\begin{array}{|c|c|}\hline \text { Ion } & {\text { Color in solution }} \\\ \hline \mathrm{H^{+ }} & {\text { Colorless }} \\ \hline \mathrm{Fe}^{2+} & {\text { Pale Green }} \\ \hline \mathrm{MnO}_{4^{-}} & {\text {Dark Purple }} \\ \hline \mathrm{Mn}^{2+} & {\text { Colorless }} \\ \hline \mathrm{Fe}^{3+} & {\text { Yellow }} \\ \hline \mathrm{K}^{+} & {\text {Colorless }} \\ \hline \mathrm{SO}_{4}^{2-} & {\text { Colorless }} \\\ \hline\end{array}$$ (c) Describe the color of the solution in the flask at the following points: (i) Before titration begins (ii) During titration prior to the endpoint (iii) At the endpoint of the titration (d) (i) If 15.55 mL of permanganate are added to reach the endpoint, what is the initial concentration of the iron (II) sulfate? (ii) The actual concentration of the \(\mathrm{FeSO}_{4}\), is 0.250 \(M\) . Calculate the percent error. (e) Could the following errors have led to the experimental result deviating in the direction that it did? You must justify your answers quantitatively. (i) 55.0 \(\mathrm{mL}\) of \(\mathrm{FeSO}_{4}\) was added to the flask prior to titration instead of 50.0 mL . (ii) The concentration of the potassium permanganate was actually 0.160 \(M\) instead of 0.150 \(M\) .

A student titrates 20.0 \(\mathrm{mL}\) of 1.0 \(M \mathrm{NaOH}\) with 2.0 \(\mathrm{M}\), \(\mathrm{HCO}_{2} \mathrm{H}\left(K_{\mathrm{a}}=1.8 \times 10^{-4}\right) .\) Formic acid is a monoprotic acid. At the equivalence point, is the solution acidic, basic, or neutral? Why? (A) Acidic; the strong acid dissociates more than the weak base (B) Basic; the only ion present at equilibrium is the conjugate base (C) Basic; the higher concentration of the base is the determining factor (D) Neutral; equal moles of both acid and base are present