Practice Test 12 - AP Chemistry

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

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1. A beaker contains a cloudy mixture of calcium carbonate (insoluble) in water. The student wants to obtain clear water and dry calcium carbonate as separate substances. Which method best achieves this?
2. A strip of magnesium metal is placed into hydrochloric acid. Bubbles form on the metal surface, and after several minutes the metal strip becomes smaller. Considering the identity of particles present before and after, which classification is most appropriate?
3. Quicklime reacts with water: $\text{CaO}(s)+\text{H}_2\text{O}(l)\rightarrow \text{Ca(OH)}_2(s)$. The mixture becomes hot. Which statement best describes the enthalpy change?
4. Aqueous calcium chloride is mixed with aqueous sodium carbonate, producing a precipitate. The balanced molecular equation is: $\mathrm{CaCl_2(aq) + Na_2CO_3(aq) \rightarrow CaCO_3(s) + 2\,NaCl(aq)}$ Which is the correct net ionic equation?
5. An element Z has atomic number 35. Which of the following is the correct ground-state electron configuration for $\mathrm{Z^-}$?
6. Hydrofluoric acid establishes the equilibrium $\text{HF}(aq) \rightleftharpoons \text{H}^+(aq) + \text{F}^-(aq)$. A student adds a soluble fluoride salt (such as NaF) to the solution at constant temperature. Which statement best describes the effect on the equilibrium position and the extent of HF dissociation?
7. A buffer is made by mixing benzoic acid, HC$_6$H$_5$CO$_2$(aq), and sodium benzoate, NaC$_6$H$_5$CO$_2$(aq). A small amount of NaOH(aq) is added. Which statement best describes how the buffer resists a large pH change, including which species reacts with the added base?
8. A student uses Beer-Lambert law, $A=\varepsilon\ell c$, to compare two measurements of the same solution at the same wavelength. Measurement 1 uses a 1.0 cm cuvette and gives $A=0.40$. Measurement 2 uses a 2.0 cm cuvette with the same solution. What absorbance is expected for Measurement 2?
9. A researcher proposes the following elementary gas-phase step: $\text{CO}(g)+\text{Cl}_2(g)\rightarrow \text{COCl}_2(g)$ Which rate law must apply if the step is elementary?
10. A 12.5 g sample of pure sodium bicarbonate, $\mathrm{NaHCO_3}$, is measured. What mass of oxygen is present in the sample? (Atomic masses: Na = 23.0 g/mol, H = 1.0 g/mol, C = 12.0 g/mol, O = 16.0 g/mol.)
11. A sample contains molecules of ammonia, NH$_3$ (polar; N–H hydrogen-bond donor; N acceptor), and phosphine, PH$_3$ (weakly polar; no significant hydrogen bonding in AP Chem). Which interaction is most responsible for ammonia having a higher boiling point than phosphine?
12. Two rigid containers of equal volume are at the same temperature. Container 1 holds $1.0\,\text{mol}$ of $\mathrm{N_2(g)}$ and container 2 holds $1.0\,\text{mol}$ of $\mathrm{O_2(g)}$. According to kinetic molecular theory, which statement is correct about the gases?
13. A student adds excess solid silver chloride, $\text{AgCl}(s)$, to $1.00\,\text{L}$ of pure water at $25^\circ\text{C}$ and stirs until equilibrium is established. The $K_{sp}$ of $\text{AgCl}$ at $25^\circ\text{C}$ is $1.6\times10^{-10}$. Dissolution: $\text{AgCl}(s)\rightleftharpoons \text{Ag}^+(aq)+\text{Cl}^-(aq)$ Assuming the initial ion concentrations are zero, what is the equilibrium concentration of $\text{Ag}^+(aq)$? ICE table (in M):

    	$\text{Ag}^+$	$\text{Cl}^-$
    I	0	0
    C	+$s$	+$s$
    E	$s$	$s$

14. A simplified PES for a third-period atom shows five peaks. From highest to lowest binding energy, the peaks are labeled 1s (height 2), 2s (height 2), 2p (height 6), 3s (height 2), and 3p (height 3). Which element is most consistent with this spectrum?
15. A proposed mechanism for the reaction $\mathrm{2NO(g) + Br_2(g) \rightarrow 2NOBr(g)}$ is shown. Step 1: $\mathrm{NO(g) + Br_2(g) \rightarrow NOBr_2(g)}$ Step 2: $\mathrm{NOBr_2(g) + NO(g) \rightarrow 2NOBr(g)}$ Which species is an intermediate in the mechanism?
16. A sample of water with mass 50.0 g at 0°C is completely melted to liquid water at 0°C. The enthalpy of fusion of water is $\Delta H_{\text{fus}}=334\ \text{J g}^{-1}$. How much energy is absorbed by the sample during this phase change?
17. Solid potassium chlorate decomposes when heated to form potassium chloride and oxygen gas: $2\text{KClO}_3(s)\rightarrow 2\text{KCl}(s)+3\text{O}_2(g)$. Which reaction type best classifies this reaction?
18. A student strikes a crystal of sodium chloride ($\text{Na}^+$ and $\text{Cl}^-$) with a hammer, and the crystal cleaves along flat planes. Which explanation best accounts for this behavior of many ionic solids?
19. A $75.0\ \text{g}$ sample of aluminum is cooled from $100.0^\circ\text{C}$ to $40.0^\circ\text{C}$. The specific heat capacity of aluminum is $0.900\ \text{J}\,\text{g}^{-1}\,\text{°C}^{-1}$. What is the heat transferred for the aluminum sample, $q$?
20. A student investigates the reaction between sodium thiosulfate and hydrochloric acid in aqueous solution. The mechanism is unchanged between trials, and no catalyst is used. Condition 1: The reactant solutions are mixed at a lower temperature. Condition 2: The reactant solutions are mixed at a higher temperature. Initial concentrations and volumes are the same. Which statement best explains why the reaction occurs faster in Condition 2 than in Condition 1, emphasizing collision effectiveness rather than simply stating that "temperature increases rate"?​

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