Practice Test 20 - High School Chemistry

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

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1. Nitrogen and hydrogen form ammonia in a sealed container: $\text{N}_2(g) + 3\text{H}_2(g) \rightarrow 2\text{NH}_3(g)$. If the container holds 18 g of $\text{N}_2$ and 6 g of $\text{H}_2$ before the reaction, what should be the total mass of gases in the container after the reaction (assuming the container stays sealed and the reaction goes to completion)?
2. A student claims: "Zinc is more reactive than copper in hydrochloric acid." Two metals are placed in separate beakers containing the same volume of 1.0 M HCl at $25^\circ\text{C}$. Evidence/observations: 1) Zinc produces many bubbles immediately and the metal piece gets noticeably smaller after 5 minutes. 2) Copper produces no visible bubbles after 5 minutes and looks unchanged. 3) Both metal samples were the same mass at the start. 4) The zinc sample was shinier than the copper sample. Which statement best evaluates the claim using the evidence?
3. Copper (Cu) is widely used for electrical wiring in homes. Which justification best connects copper's periodic-table classification and atomic structure to its high electrical conductivity?
4. Hydrogen peroxide decomposes as shown: $\mathrm{2H_2O_2 \rightarrow 2H_2O + O_2}$ What is the mole ratio of hydrogen peroxide ($\mathrm{H_2O_2}$) to oxygen gas ($\mathrm{O_2}$)?
5. A maintenance team must choose a material for a drain pipe carrying warm (50–70°C) cleaning solution that is sometimes basic (pH ~11) and sometimes mildly acidic (pH ~5). Requirements: must not corrode quickly (critical), must tolerate the temperature range, and must be reasonably affordable. Options: - PVC: good resistance to many acids/bases; temperature limit around 60°C for long-term use; low cost. - CPVC: better high-temperature tolerance (~90°C); good chemical resistance; higher cost than PVC. - Galvanized steel: strong; can corrode in acidic/basic solutions over time; moderate cost.
6. A student heats a small amount of candle wax in a metal spoon until it becomes a clear liquid. The student then removes the spoon from the heat and lets it cool. Observations: - Wax changes from solid to liquid while heating. - No bubbling or smoke is observed. - The wax returns to a solid when cooled. - The wax is the same color before and after. Based on the evidence, did a chemical reaction occur? Choose the best CER-style justification.
7. All three elements are in period 3: sodium (Na) is in group 1, aluminum (Al) is in group 13, and chlorine (Cl) is in group 17. Which element has the smallest atomic radius?
8. Two trials use the same reactants in solution at the same temperature. Trial 1 uses a small amount of one reactant dissolved in the solution. Trial 2 uses a larger amount of that same reactant in the same volume, and the reaction is faster. Which collision-theory explanation best describes what changes from Trial 1 to Trial 2?
9. A student burns a small piece of wood in a fire-safe container. Before, it is solid wood; after, there is gray ash and smoke was produced during burning. What type of change is this?
10. Two solutions are combined in a beaker. Before mixing: - 30.0 mL calcium chloride solution, CaCl2(aq): mass = 31.2 g, temperature = 21.0°C, appearance = clear/colorless - 30.0 mL sodium carbonate solution, Na2CO3(aq): mass = 31.0 g, temperature = 21.0°C, appearance = clear/colorless After mixing: - Mixture: mass = 62.2 g, temperature = 21.5°C, appearance = cloudy with a white solid present Which observation is the best evidence that a new substance formed?
11. A reaction is observed to be endothermic (the surroundings get cooler). Which bond-energy explanation is most consistent with an endothermic reaction?
12. A student opens a bottle of carbonated water. Bubbles rise to the surface and the drink fizzes, but nothing else changes. Which statement best explains why this is NOT strong evidence of a chemical reaction?
13. A simplified fission reaction is shown: $^{235}_{92}\text{U} + {}^{1}_{0}n \rightarrow {}^{144}_{56}\text{Ba} + {}^{89}_{36}\text{Kr} + 3\,{}^{1}_{0}n.$ What nuclear process does this equation represent?
14. A student argues: "A campfire can release a lot of heat, so chemical reactions must release more energy per atom than nuclear reactions." Which response best corrects the student's misunderstanding?
15. Using the balanced equation: $\text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3$ If $6.0 \text{mol}$ of $\text{H}_2$ react completely, how many moles of $\text{NH}_3$ are formed?
16. Use the periodic trend for electronegativity. The following are main-group elements in period 2: - Li (group 1) - C (group 14) - F (group 17) Which element is most electronegative?
17. Neon has the electron configuration $1s^2\,2s^2\,2p^6$ and is in group 18. Under normal conditions, neon does not form compounds easily. How does neon's atomic structure explain this lack of reactivity?
18. Zinc granules are added to 25 mL of hydrochloric acid at 25°C, producing bubbles of hydrogen gas. Trial 1 uses 1.0 M HCl. Trial 2 uses 0.50 M HCl, with the same volume of acid, same mass of zinc, and the same temperature. What happens to the reaction rate in Trial 2 compared with Trial 1?
19. A student mixes vinegar and baking soda in a cup. The mixture immediately fizzes and produces many bubbles, and the cup feels cooler to the touch. Classify the change based on these observations.
20. A student investigates how concentration affects the rate of a reaction between sodium thiosulfate solution and hydrochloric acid (a cloudy sulfur precipitate forms). The temperature is kept constant at 25°C. Trial 1: 0.10 M sodium thiosulfate Trial 2: 0.20 M sodium thiosulfate All other conditions (volume, acid concentration, mixing) are the same. Compared with Trial 1, what happens to the reaction rate in Trial 2, and why?

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