Practice Test 43 - 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 class compares safety posters: one about gasoline fires (chemical combustion) and one about radiation from radioactive materials (nuclear decay). Without doing any calculations, which statement best explains why nuclear processes are associated with much larger energy release per atom than chemical processes?
2. A strip of magnesium is ignited in air. It burns with a bright white light and leaves behind a white powder. What kind of change is this?
3. Carbon has 4 valence electrons (group 14). In many compounds, carbon forms 4 covalent bonds (for example, CH$_4$). How does carbon's valence electron structure explain this bonding tendency?
4. A student heats a small amount of a solid in a metal spoon over a flame. The solid glows brightly for a moment, gives off a little smoke, and afterward a different-looking powdery residue remains. Which change provides the strongest evidence of a chemical reaction?
5. Two clear solutions are mixed in a beaker. In one trial, the solutions are cold and the visible change (like cloudiness or a color change) takes a long time. In a second trial, the same volumes and same solutions are warmed first, and the visible change happens much faster. Using collision theory, which particle-level explanation best accounts for the faster reaction in the warmed trial?
6. Four elements are listed with their periodic positions: - lithium (Li): Group 1, Period 2 - sodium (Na): Group 1, Period 3 - potassium (K): Group 1, Period 4 - cesium (Cs): Group 1, Period 6 Which is expected to be most reactive with water?
7. Calcium carbonate reacts with hydrochloric acid to form carbon dioxide gas: $\text{CaCO}_3\text{(s)} + 2\text{HCl(aq)} \rightarrow \text{CaCl}_2\text{(aq)} + \text{CO}_2\text{(g)} + \text{H}_2\text{O(l)}$ A student runs the reaction at 25°C with 1.0 M HCl. In one trial they use large marble chips. In another trial they use the same mass of marble crushed into a powder. All other conditions are the same. How does crushing the marble affect the reaction rate, and why?
8. A neutral atom has 11 protons and 12 neutrons. What is its mass number ($A$)?
9. Chlorine (Cl) is in Group 17 and has 7 valence electrons (electron configuration ends in 3s² 3p⁵). Chlorine often forms Cl⁻ in ionic compounds such as NaCl. Why does chlorine tend to form a −1 ion?
10. Consider the transformation: sulfur atom (S) → sulfide ion (S²⁻). Sulfur is in Group 16 and has 6 valence electrons. Which statement best explains why the sulfide ion has a 2− charge?
11. The decomposition of calcium carbonate is $\mathrm{CaCO_3(s) \rightarrow CaO(s) + CO_2(g)}$ with $\Delta H = +178\ \mathrm{kJ/mol}$. What does the sign of $\Delta H$ tell you about this reaction at constant pressure?
12. Three elements are in the same group (group 2, alkaline earth metals): beryllium (Be) is in period 2, magnesium (Mg) is in period 3, and calcium (Ca) is in period 4. Which element has the lowest first ionization energy?
13. What coefficients balance the equation using the smallest whole numbers? KClO3 → KCl + O2​
14. In the nuclear equation $^{210}_{84}\text{Po} \rightarrow \,^{206}_{82}\text{Pb} + X,$ what is $X$?
15. Two students perform the same reaction: magnesium ribbon + hydrochloric acid. They use the same length of magnesium ribbon and the same temperature (25°C). Student 1 uses 25 mL of 0.5 M HCl; Student 2 uses 25 mL of 2.0 M HCl. Student 2 observes much faster bubbling and the magnesium disappears sooner. Which explanation best matches collision theory?
16. Hydrogen peroxide decomposes slowly at room temperature: $2\text{H}_2\text{O}_2\text{(aq)} \rightarrow 2\text{H}_2\text{O(l)} + \text{O}_2\text{(g)}$ A student has a bottle of 3% $\text{H}_2\text{O}_2$ stored at 20°C. They move it to a refrigerator at 4°C (same concentration; no catalyst added). What happens to the decomposition rate, and why?
17. A student burns 30 g of magnesium ribbon in air in an open container: $2\text{Mg}(s) + \text{O}_2(g) \rightarrow 2\text{MgO}(s)$ After burning, the mass of the magnesium oxide collected is 50 g. Which statement best explains why the product mass is greater than the original magnesium mass?
18. A deuterium nucleus and a tritium nucleus combine to form a helium nucleus, plus a neutron, releasing energy. What type of nuclear process is this?
19. A student repeated the same titration three times to check reliability. Each trial used 25.0 mL of an acid solution and NaOH(aq) from a buret. The endpoint was the first permanent faint pink color (phenolphthalein indicator). The volume of NaOH needed to reach the endpoint was recorded. Data table: - Trial 1 NaOH volume (mL): 18.42 - Trial 2 NaOH volume (mL): 18.39 - Trial 3 NaOH volume (mL): 18.44 Which statement best describes the data quality based on these results?
20. Aluminum (Al) is in group 13 (3 valence electrons), magnesium (Mg) is in group 2 (2 valence electrons), and sodium (Na) is in group 1 (1 valence electron). Which statement best connects valence electrons to their typical ion formation and reactivity as metals?

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