Practice Test 6 - AP Chemistry

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

Solid carbon dioxide at its sublimation temperature is converted to carbon dioxide gas at the same temperature. If $\Delta H_{sub}$ for $\text{CO}_2$ is $25.2\ \text{kJ/mol}$ , how much energy is absorbed when $44\ \text{g}$ of $\text{CO}_2(s)$ sublimates? (Molar mass of $\text{CO}_2$ = $44\ \text{g/mol}$ .)
A buffer contains $0.60\ \text{M}$ $\text{HCO}_3^-$ and $0.20\ \text{M}$ $\text{H}_2\text{CO}_3$ . Given $\text{p}K_a(\text{H}_2\text{CO}_3)=6.35$ , what is the pH of the buffer?
A buffer is made from $0.10\ \text{M}$ $\text{HClO}$ and $0.30\ \text{M}$ $\text{ClO}^-$ . Given $\text{p}K_a(\text{HClO})=7.53$ , what is the pH of the buffer?
Two different solutes, P and Q, are measured at the same wavelength in 1.0 cm cuvettes. Both solutions have the same concentration, but $\varepsilon_P = 600\ \text{M}^{-1}\text{cm}^{-1}$ and $\varepsilon_Q = 200\ \text{M}^{-1}\text{cm}^{-1}$ . Which comparison is correct for their absorbances, $A_P$ and $A_Q$ ?
Steam at $100^\circ\text{C}$ condenses to liquid water at $100^\circ\text{C}$ on a cold window. The window warms as droplets form. Which statement correctly describes the condensation process and the sign of $\Delta H$ for $\text{H}_2\text{O}(g)\rightarrow\text{H}_2\text{O}(l)$ ?
A student prepares a buffer by mixing acetic acid, $\mathrm{HC_2H_3O_2}$ , and sodium acetate, $\mathrm{NaC_2H_3O_2}$ , so that the solution contains comparable amounts of $\mathrm{HC_2H_3O_2(aq)}$ and $\mathrm{C_2H_3O_2^-(aq)}$ . A small amount of $\mathrm{HCl(aq)}$ is added. Which statement best describes the primary reaction that helps the solution resist a large change in pH?
A compound has molar absorptivity $\varepsilon = 250\ \text{L mol}^{-1}\text{cm}^{-1}$ at a particular wavelength. A solution of this compound with concentration $c = 0.012\ \text{M}$ is measured and gives absorbance $A = 0.90$ . What is the path length $\ell$ of the cuvette?
Solid ammonium chloride, NH $_4$ Cl(s), is placed in water and dissolves completely to form NH $_4^+$ (aq) and Cl $^-$ (aq) at constant temperature (assume the temperature is maintained by the surroundings). For the dissolving process in the solution as the system, does the entropy increase, decrease, or remain approximately constant?
A student observes that in an electrochemical cell, the reaction proceeds on its own once the circuit is closed, and the device can be used as a power source for a small calculator. No external battery is connected. Which statement correctly classifies the cell and its defining feature?
A 100 g piece of aluminum is cooled from $50.0^{\circ}\text{C}$ to $20.0^{\circ}\text{C}$ . The specific heat capacity of aluminum is $0.900\ \text{J}\,\text{g}^{-1}\,^{\circ}\text{C}^{-1}$ . What is the heat transferred for the aluminum, $q$ , in joules?
Molten (liquid) sodium chloride is cooled until it solidifies to NaCl(s) in a closed crucible. Considering only the phase change from liquid to solid for the system, does entropy increase, decrease, or remain approximately constant?
At 1 atm, solid carbon dioxide (dry ice) sublimes at -78.5°C, changing directly into a gas. Which statement best compares the properties of the $CO_2$ molecules in the solid and gaseous phases?
A bond forms between nitrogen and oxygen in NO. The electronegativity values are approximately $EN(\text{N})=3.0$ and $EN(\text{O})=3.4$ , so $\Delta EN \approx 0.4$ . Which classification best describes the N–O bond?
Aqueous sodium thiosulfate reacts with aqueous hydrochloric acid to form sulfur dioxide gas and elemental sulfur. The balanced molecular equation is: $\mathrm{Na_2S_2O_3(aq) + 2\,HCl(aq) \rightarrow 2\,NaCl(aq) + SO_2(g) + S(s) + H_2O(l)}$ Which is the correct net ionic equation?
A particulate diagram representing the equilibrium state for the gas-phase reaction $2 AB(g) \rightleftharpoons A_2(g) + B_2(g)$ is contained in a 1 L box. The diagram shows 4 molecules of AB, 6 molecules of $A_2$ , and 6 molecules of $B_2$ . Which statement is consistent with this representation?
In the reaction $\mathrm{H_3O^+(aq) + NO_2^-(aq) \rightarrow HNO_2(aq) + H_2O(l)}$ , which species is the conjugate base of $\mathrm{H_3O^+}$ ?
A $7.0\times10^{-3}\,\text{M}$ solution of KOH $(aq)$ is prepared at $25^\circ\text{C}$ . Assuming complete dissociation, what is $[\text{OH}^-]$ in the solution?
A student examines the following reaction: $\mathrm{HCl(g) + NH_3(g) \rightarrow NH_4^+Cl^-(s)}$ . According to the Brønsted–Lowry definition, which species acts as the base?
Consider the reaction $\mathrm{HClO_4(aq) + H_2O(l) \rightarrow H_3O^+(aq) + ClO_4^-(aq)}$ . Which species is the conjugate base of the acid?
Propane combusts completely in oxygen to form carbon dioxide and water vapor: $\mathrm{C_3H_8(g) + 5O_2(g) \rightarrow 3CO_2(g) + 4H_2O(g)}$ . Which reaction type best classifies this reaction?

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