Practice Test 9 - AP Chemistry

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

Start practice test

1. Two solids are compared at $25^\circ\text{C}$. Solid X is brittle, has a high melting point, and is nonconductive as a solid. Solid Y is malleable, lustrous, and conductive as a solid. Which pairing of solid types is most consistent with these observations?
2. A student is told that a certain reaction can form either product R1 or product R2. The pathway to R1 has the lower activation energy, while R2 is more stable (lower energy product). The student performs the reaction at moderate temperature but removes product continuously as it forms, preventing the system from approaching equilibrium. Which statement best describes what is favored under these conditions?
3. An element Z has a mass spectrum with two peaks at $m/z=10$ and $m/z=11$ of approximately equal height (relative abundance 50 and 50). Assuming singly charged ions, what is the average atomic mass of Z?
4. Excess solid zinc sulfide, $\text{ZnS}(s)$, is added to pure water at $25^\circ\text{C}$ and allowed to reach equilibrium. The $K_{sp}$ of $\text{ZnS}$ is $1.0\times10^{-24}$. Dissolution: $\text{ZnS}(s)\rightleftharpoons \text{Zn}^{2+}(aq)+\text{S}^{2-}(aq)$ Assuming initial ion concentrations are zero, what is the molar solubility of $\text{ZnS}$? ICE table (in M):

   	$\text{Zn}^{2+}$	$\text{S}^{2-}$
   I	0	0
   C	+$s$	+$s$

   | E | $s$ | $s$ |​
5. A buffer solution contains nitrous acid, $\mathrm{HNO_2(aq)}$, and sodium nitrite, $\mathrm{NaNO_2(aq)}$, with $\mathrm{HNO_2}$ present in excess. A small amount of strong base is added. Which statement best describes the immediate effect on the buffer components?​​
6. Nitrogen gas and hydrogen gas react to form ammonia according to the balanced equation: $\;\text{N}_2(g)+3\text{H}_2(g)\rightarrow 2\text{NH}_3(g)$. If $0.900\ \text{mol}$ of $\text{H}_2$ reacts completely with excess $\text{N}_2$, how many moles of $\text{NH}_3$ are produced?
7. A crystal is composed of Fe$^{3+}$ and Cl$^-$ ions in a repeating pattern. Which formula represents the simplest charge-balanced composition of the ionic solid?
8. A proposed mechanism for the reaction $\mathrm{NO_2(g) + CO(g) \rightarrow NO(g) + CO_2(g)}$ is shown below: Step 1 (fast, reversible): $\mathrm{NO_2 + NO_2 \rightleftharpoons N_2O_4}$ Step 2 (slow): $\mathrm{N_2O_4 + CO \rightarrow NO + NO_3 + CO_2}$ Step 3 (fast): $\mathrm{NO_3 + NO_2 \rightarrow NO + O_2 + NO_2}$ Based only on the rate-determining step, which rate law is implied by the mechanism?
9. For a reaction that is found to be third order overall, which of the following are the correct units for the rate constant, k?
10. The equilibrium $\mathrm{H_2(g) + Cl_2(g) \rightleftharpoons 2HCl(g)}$ is established in a 1.0 L flask. Initially, $[\mathrm{H_2}]=0.010\,\mathrm{M}$, $[\mathrm{Cl_2}]=1.00\,\mathrm{M}$, and $[\mathrm{HCl}]=0\,\mathrm{M}$. At this temperature, $K_c=9.0\times 10^{-4}$. Using an ICE table and treating $[\mathrm{Cl_2}]$ as effectively constant, what is the equilibrium concentration of $\mathrm{HCl}$?
11. When hydrogen gas is ignited in oxygen gas, liquid water forms: $\mathrm{2H_2(g) + O_2(g) \rightarrow 2H_2O(l)}$. Which classification best describes this reaction?
12. Element R produces a mass spectrum with peaks at $m/z=78$ (relative abundance 50) and $m/z=80$ (relative abundance 50). Assuming $+1$ ions, what is the average atomic mass of R?
13. A student studies the reaction $\mathrm{C_5H_5N(aq) + H_2O(l) \rightleftharpoons C_5H_5NH^+(aq) + OH^-(aq)}$ (pyridine reacting with water). Which species is the conjugate acid of $\mathrm{C_5H_5N}$?
14. A system is at equilibrium for $2\text{NO}(g)+\text{O}_2(g)\rightleftharpoons 2\text{NO}_2(g)$. The equilibrium concentrations are $[\text{NO}]=0.10\,\text{M}$, $[\text{O}_2]=0.20\,\text{M}$, and $[\text{NO}_2]=0.40\,\text{M}$. What is $K_c$?
15. The equilibrium reaction $\mathrm{A(g) + B(g) \rightleftharpoons C(g)}$ has equilibrium constant $K$. A student adds this reaction to its reverse, $\mathrm{C(g) \rightleftharpoons A(g) + B(g)}$, to obtain the net equation $\mathrm{0 \rightleftharpoons 0}$. What is the equilibrium constant $K_{\text{new}}$ for the net equation in terms of $K$?
16. In a kinetics model, the following is given as a single elementary step: $\text{CH}_3\text{Br}(aq)+\text{OH}^-(aq)\rightarrow \text{CH}_3\text{OH}(aq)+\text{Br}^-(aq)$ Which rate law follows from the definition of an elementary reaction step?
17. A student adds a few crystals of potassium permanganate (KMnO4) to a large beaker of water and stirs. The entire liquid becomes uniformly purple. Which statement is correct?
18. A student connects a Fe(s)|Fe$^{2+}$(aq) half-cell to a Ag(s)|Ag$^+$(aq) half-cell under standard conditions. The standard reduction potentials are: Fe$^{2+}$ + 2e$^-$ → Fe(s), $E^\circ=-0.44\ \text{V}$; Ag$^+$ + e$^-$ → Ag(s), $E^\circ=+0.80\ \text{V}$. If electrons flow through the external circuit from the Fe electrode to the Ag electrode, which statement is correct about the overall cell reaction?
19. A solution absorbs light at 430 nm with molar absorptivity $\varepsilon = 150\,\text{M}^{-1}\text{cm}^{-1}$. A student uses a cuvette with $\ell = 2.00\,\text{cm}$ and measures $A = 0.60$. What is the concentration of the solution?
20. Aqueous methylamine reacts with water: $\mathrm{CH_3NH_2(aq) + H_2O(l) \rightleftharpoons CH_3NH_3^+(aq) + OH^-(aq)}$. Which species is the conjugate acid of $\mathrm{CH_3NH_2}$?

Practice tests