Practice Test 13 - High School Chemistry

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

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1. A line graph shows product concentration $[P]$ versus time for two reactions, A and B. - Reaction A: $[P]$ rises quickly at first (steep slope) and reaches a plateau early. - Reaction B: $[P]$ rises slowly (gentle slope) and reaches a plateau later. Which conclusion is best supported by the graph?
2. A student investigated how temperature affects the rate of reaction between magnesium ribbon and $1.0\,\text{M}$ hydrochloric acid. In each condition, a $0.50\,\text{g}$ piece of Mg was added to $25.0\,\text{mL}$ of acid, and the time for the Mg to completely dissolve was recorded. Based on the data, what relationship is supported between temperature and time to dissolve?
3. A student compares three elements: sodium (group 1), magnesium (group 2), and aluminum (group 13). All are in period 3, but sodium reacts most vigorously with water, magnesium reacts more slowly, and aluminum is much less reactive (it often appears unreactive). Which explanation best uses valence electrons to explain this trend?
4. A student performs the same reaction (magnesium ribbon + hydrochloric acid) under two conditions. The acid concentration, volume, and Mg ribbon size are the same. Condition X: room temperature (22°C) → reaction completes in ~50 s Condition Y: ice bath (5°C) → reaction completes in ~140 s Which statement best explains why Condition Y is slower?
5. Sodium reacts with chlorine gas to form sodium chloride: $\textbf{2Na} + \textbf{Cl}_2 \rightarrow \textbf{2NaCl}$ If $7.0\ \text{mol}$ of $\text{Na}$ react completely, how many moles of $\text{NaCl}$ form?
6. A reaction energy diagram shows a single curve that rises to one highest point and then falls. What does the highest point (the peak) represent?
7. In the equation $^{210}_{84}\mathrm{Po} \rightarrow ^{206}_{82}\mathrm{Pb} + X,$ identify particle $X$.
8. Magnesium has electron configuration [Ne]3s2 and aluminum has electron configuration [Ne]3s2 3p1. In period 3, aluminum has a smaller atomic radius than magnesium. Which explanation best accounts for this trend using electron configuration?
9. A student adds a teaspoon of table salt (NaCl) to 100 mL of water and says, "The salt disappeared, so it must have undergone a chemical change." Your teacher asks you to design an investigation to test whether dissolving salt in water is a chemical change or a physical change. Which investigation design best answers the testable question using observable evidence and a fair comparison?
10. Aluminum (Al) is in group 13 and has 3 valence electrons. It commonly forms the ion Al. Which statement best explains why Al forms a +3 ion?
11. A neutral atom has 20 neutrons and mass number 39. What element is it (identify by symbol)?
12. A teacher says: "If you compare one fission event to one combustion event, the nuclear event releases enormously more energy." Which reason best supports this claim without requiring calculations?
13. Sulfur trioxide forms by $\,2\text{SO}_2 + \text{O}_2 \rightarrow 2\text{SO}_3\,$. If you start with $1.0\ \text{mol SO}_2$ and $2.0\ \text{mol O}_2$, which reactant is limiting?
14. A solid reactant is tested in two forms: a single large chunk and a fine powder. The powder reacts noticeably faster when placed into the same liquid reactant. Using collision theory, what is the best particle-level reason for the faster reaction with the powder?
15. A student investigates the reaction between sodium thiosulfate and hydrochloric acid (the mixture turns cloudy as sulfur forms). The student keeps temperature constant at 25°C and uses the same volumes each time. They change only the concentration of sodium thiosulfate from 0.10 M to 0.20 M. Based on collision theory, how should the reaction rate change?
16. A reaction is performed in an open flask: $\mathrm{X(aq) \rightarrow Y(aq) + Z(g)}$. The flask and solution have a mass of 200 g before the reaction. After the reaction, the flask and remaining liquid have a mass of 193 g. Which conclusion is most consistent with conservation of mass?
17. Which set of coefficients balances the equation (smallest whole numbers)? H2O2 → H2O + O2​
18. A camping stove uses a small fuel canister that sits near a flame. The canister's outer material must not ignite easily, must remain chemically stable when warmed, and must not produce toxic fumes if briefly exposed to heat. Which chemical property should the designer prioritize most for safety?
19. Two beakers start at 22°C. In Beaker 1, chemicals are mixed and the temperature rises to 30°C. In Beaker 2, chemicals are mixed and the temperature drops to 16°C. Which choice correctly classifies both processes and the energy flow direction?
20. In the balanced equation $\mathrm{4Fe + 3O_2 \rightarrow 2Fe_2O_3}$ what is the mole ratio of oxygen gas ($\mathrm{O_2}$) to iron(III) oxide ($\mathrm{Fe_2O_3}$)?

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