Practice Test 5 - AP Chemistry

20 questions. Answer them in any order, then submit to see your score and every explanation.

A student connects two half-cells with a salt bridge: Sn(s) in Sn(NO $_3$ ) $_2$ (aq) and Pb(s) in Pb(NO $_3$ ) $_2$ (aq). When the circuit is completed through a light-emitting diode (LED), the LED glows without any external power supply. After several minutes, the mass of one electrode decreases while the other increases. Which statement correctly classifies the process and identifies a defining feature?
A reaction is at equilibrium in a sealed container: $\text{CH}_3\text{COOH}(aq) \rightleftharpoons \text{CH}_3\text{COO}^-(aq) + \text{H}^+(aq)$ . The stress applied is the addition of $\text{H}^+(aq)$ to the solution. How will the system shift to re-establish equilibrium?
Two bonds are compared in similar environments: a $\mathrm{C-O}$ single bond and a $\mathrm{C=O}$ double bond. Which bond is expected to have the greater bond strength?
A galvanic cell is constructed with half-cells $\text{Ni}(s)|\text{Ni}^{2+}(aq)$ and $\text{Cu}^{2+}(aq)|\text{Cu}(s)$ . The spontaneous overall reaction under standard conditions is $\text{Ni}(s)+\text{Cu}^{2+}(aq)\rightarrow \text{Ni}^{2+}(aq)+\text{Cu}(s).$ Compared with standard conditions, the $\text{Cu}^{2+}$ concentration is decreased below $1.0\,\text{M}$ while all other species remain at standard conditions. Using qualitative Nernst reasoning (through the effect on $Q$ ), how does $E_\text{cell}$ change and does the cell remain spontaneous?
A galvanic cell is built under standard conditions from a Mg(s)|Mg $^{2+}$ (aq) electrode and a Cd(s)|Cd $^{2+}$ (aq) electrode. The standard reduction potentials are: Mg $^{2+}$ + 2e $^-$ $\rightarrow$ Mg(s), $E^\circ = -2.37\,\text{V}$ ; Cd $^{2+}$ + 2e $^-$ $\rightarrow$ Cd(s), $E^\circ = -0.40\,\text{V}$ . The student labels Cd as the anode and Mg as the cathode. Based on the provided $E^\circ$ values, which statement is correct about the cell reaction as labeled?
A student compares the solubility of solid calcium fluoride, $\text{CaF}_2(s)$ , in two solutions at the same temperature: Solution 1 is pure water, and Solution 2 is 0.10 M HCl. How does lowering the pH affect the solubility of $\text{CaF}_2(s)$ , and why?
A student observes bubbles when solid sodium bicarbonate is added to aqueous hydrochloric acid. The products are aqueous sodium chloride, liquid water, and carbon dioxide gas. Which balanced molecular equation best represents this reaction (including physical states)?
Excess solid silver bromide, $\text{AgBr}(s)$ , is shaken with pure water at $25^\circ\text{C}$ until equilibrium is reached. The solubility product constant is $K_{sp}(\text{AgBr})=2.5\times10^{-13}$ . What is the equilibrium concentration of $\text{Br}^-(aq)$ ? (Assume volume change is negligible.)
A student compares two dissolutions at $25^\circ\text{C}$ : - Process 1: $\Delta H_{\text{soln}} > 0$ and $\Delta S_{\text{soln}} > 0$ - Process 2: $\Delta H_{\text{soln}} > 0$ and $\Delta S_{\text{soln}} < 0$ Which statement correctly describes thermodynamic favorability at $25^\circ\text{C}$ ?
Phosphorus trichloride, $\text{PCl}_3$ , has a total of 26 valence electrons. In the correct Lewis structure (P central with single bonds), how many lone pairs are on phosphorus?
A student constructs a cell with two half-cells connected by a salt bridge and a wire. When the circuit is closed, the voltage is positive and electrical energy is delivered to a resistor in the circuit, causing it to warm slightly. No external power supply is connected. Which statement correctly classifies the process and its defining feature?
In a sealed flask at constant temperature, the equilibrium $\mathrm{2NO(g) + O_2(g) \rightleftharpoons 2NO_2(g)}$ has $K_p = 6.0\times10^1$ . The system is initially at equilibrium. A small amount of $\mathrm{O_2(g)}$ is removed, and immediately afterward $Q_p$ is found to be $9.0\times10^1$ . As equilibrium is reestablished, what shift occurs?
Sodium bicarbonate reacts with hydrochloric acid according to the balanced equation below: $\text{NaHCO}_3(aq)+\text{HCl}(aq)\rightarrow \text{NaCl}(aq)+\text{H}_2\text{O}(l)+\text{CO}_2(g)$ If $25.0\ \text{mL}$ of $0.200\ \text{M}$ $\text{NaHCO}_3(aq)$ reacts with excess $\text{HCl}(aq)$ , how many moles of $\text{CO}_2(g)$ are produced?
A student compares pure aluminum (Al) to an alloy made by mixing Al with a small amount of magnesium (Mg). Both solids are metallic. Which statement best describes what happens to the valence electrons in the alloy compared with pure Al?
Consider the reaction in water: $\mathrm{CH_3COOH(aq) + H_2O(l) \rightleftharpoons CH_3COO^-(aq) + H_3O^+(aq)}$ . Which species is the conjugate base of $\mathrm{CH_3COOH}$ ?
Magnesium metal reacts with hydrochloric acid to produce hydrogen gas: $\mathrm{Mg(s) + 2HCl(aq) \rightarrow MgCl_2(aq) + H_2(g)}$ . Which reaction type best classifies this reaction?
A metal is described as a lattice of cations surrounded by a "sea" of delocalized electrons. Which statement best explains why metals are typically good conductors of electricity in the solid state?
When a sample of a pure liquid is heated but remains in the liquid phase, what is the primary effect on the particles at the molecular level?
Methane, $\mathrm{CH_4}$ , and chloromethane, $\mathrm{CH_3Cl}$ , have similar sizes, but $\mathrm{CH_3Cl}$ has a polar $\mathrm{C\!- Cl}$ bond and a net dipole. Which intermolecular force is present in $\mathrm{CH_3Cl}$ but not in $\mathrm{CH_4}$ ?
A hydrogen atom absorbs a photon and an electron transitions from $n=1$ to $n=3$ . In a separate experiment, a hydrogen atom absorbs a photon and an electron transitions from $n=1$ to $n=2$ . Which absorbed photon has the greater energy?

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