Practice Test 14 - High School Chemistry

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

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1. Two product concentration curves, A and B, are shown on the same concentration-versus-time graph. Both start near zero and increase. Curve A rises more steeply at first and reaches a plateau sooner than curve B. Which conclusion is best supported by the graph?
2. Neon (Ne) is a noble gas in Group 18 and Period 2. In a sealed tube, neon gas does not react with oxygen or water vapor under normal conditions. Which justification best explains neon's lack of reactivity?
3. Two different flasks contain the same reactant molecules in the gas phase. Flask 1 is kept cool; Flask 2 is warmed. In Flask 2, the reaction proceeds faster. Which statement best connects particle motion to the faster reaction in Flask 2 using collision theory?
4. A student engineering team is building a small electrolysis demonstration that uses saltwater (NaCl solution) and a low-voltage power supply. They need electrode material. Requirements: must conduct electricity, should resist corrosion in saltwater, and must be safe and affordable for a classroom. Which material is the best trade-off? Options: - Graphite (carbon) rod: conducts; generally corrosion-resistant; can slowly crumble/flake; low cost. - Iron nail: very cheap and conducts; corrodes/rusts quickly in saltwater, changing results. - Silver wire: conducts very well and resists corrosion; too expensive for class sets.
5. Two clear solutions are mixed in a beaker. In one trial the beaker is kept in an ice bath, and in another trial the beaker is warmed in hot water. The warmed mixture turns cloudy much sooner, showing the reaction happens faster. Using collision theory, which statement best explains why warming speeds up the reaction at the particle level?
6. Propane combusts according to $\mathrm{C_3H_8(g) + 5\,O_2(g) \rightarrow 3\,CO_2(g) + 4\,H_2O(l)}$ with $\Delta H = -2220\ \mathrm{kJ/mol}$. Compared with a reaction that has $\Delta H = -150\ \mathrm{kJ/mol}$, what does the magnitude of $\Delta H$ suggest?
7. A lab needs tweezers for handling small pieces of solid sodium hydroxide (a strong base). Requirements: (1) must not corrode quickly in contact with strong base, (2) must be safe to handle (no toxic coatings), and (3) must be reasonably priced. Options: - Stainless steel: good corrosion resistance; durable; higher cost. - Plain carbon steel: cheap; rusts/corrodes readily, especially with moisture and chemicals. - Plastic (nylon): inexpensive; resists bases well; but can soften if exposed to heat and may not grip as firmly. Which is the best trade-off for routine room-temperature handling of NaOH pellets?
8. Balance the equation using the smallest whole-number coefficients: Ca(OH)2 + HCl → CaCl2 + H2O​​
9. A student monitored the temperature change during the reaction of hydrochloric acid with sodium hydroxide. Each trial mixed $25.0\,\text{mL}$ of $1.0\,\text{M}$ HCl with $25.0\,\text{mL}$ of $1.0\,\text{M}$ NaOH. The only difference was the starting temperature of both solutions (they were pre-warmed or pre-cooled together). The student recorded the initial and peak temperature. What trend is visible in the data?
10. Balance the decomposition reaction using the smallest whole-number coefficients: H2O2 → H2O + O2
11. A student measured the pH during a titration of $25.0\,\text{mL}$ of $0.10\,\text{M}$ HCl with $0.10\,\text{M}$ NaOH. The pH was recorded after each addition of NaOH.

    NaOH added (mL)	pH
    0.0	1.2
    10.0	1.6
    20.0	2.0
    25.0	7.0

    Which trend is visible in the data?
12. A student mixes two solutions in a test tube and records observations. Data/observations: - Solution 1: clear, colorless, 10 mL at 21.0°C - Solution 2: clear, colorless, 10 mL at 21.0°C - After mixing: the solution turns pink and stays pink for at least 10 minutes. - Temperature increases to 26.5°C. - No bubbles are seen. - No solid forms. Which CER-style justification best supports whether a chemical reaction occurred?
13. A student mixes silver nitrate solution (AgNO$_3$(aq)) with sodium chloride solution (NaCl(aq)) in a beaker. Data: - Before: 20.0 g AgNO$_3$(aq) (clear, 22.0°C) + 20.0 g NaCl(aq) (clear, 22.0°C) - After mixing: 40.0 g mixture, 22.0°C, cloudy with a white solid present Which statement best uses the data as evidence?​
14. Aluminum (Al) has atomic number 13. What is the electron configuration of a neutral aluminum atom using Aufbau filling order (1s, 2s, 2p, 3s, 3p)?
15. A prototype garden irrigation connector uses a brass fitting screwed into an aluminum manifold because both are easy to machine. After 3 months outdoors, white powdery corrosion appears around the joint, and the aluminum threads become rough and weakened. The brass fitting looks mostly unchanged. The leak starts at the joint. Which refinement most directly targets the likely cause of the failure?
16. Magnesium oxide forms as: $2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}$ If you start with $6.0\,\text{mol}$ of Mg and $2.0\,\text{mol}$ of $\text{O}_2$, which reactant is in excess (left over after the reaction stops)?
17. A marine hardware company needed fasteners for docks exposed to salt spray. They selected 316 stainless steel instead of zinc-plated carbon steel. After 2 years at a coastal test site, 316 fasteners showed minimal surface change, while zinc-plated fasteners had rust streaks and several seized threads. Which reasoning best justifies the original selection?
18. Students test the research question: How does solution temperature affect electrical conductivity? They prepare 200 mL of 0.10 M NaCl solution and pour 50.0 mL into each of four beakers. They place the beakers in water baths to reach 10°C, 20°C, 30°C, and 40°C, then measure conductivity with the same conductivity probe after the temperature stabilizes for 2 minutes. What is the dependent variable?
19. Which element (atomic number 1-20) has the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁴?
20. A student performs the same gas-producing reaction two ways: Reaction: X(aq) + Y(aq) → Z(aq) + CO$_2$(g) - Trial 1 (open cup): total mass before = 150 g; total mass after = 146 g - Trial 2 (sealed flask): total mass before = 150 g; total mass after = 150 g Which statement best explains the different results?

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