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Practice Test 17 - High School Chemistry

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

  1. A student claims: "A chemical reaction occurred when magnesium ribbon was placed into hydrochloric acid." Evidence collected: 1) Bubbles formed on the magnesium surface within 5 seconds. 2) The temperature of the beaker increased from 21.8°C to 28.6°C. 3) The magnesium ribbon became smaller over 2 minutes. 4) The hydrochloric acid solution was colorless before and after. Which statement best evaluates whether the evidence supports the claim?
  2. A teacher demonstrates the reaction between magnesium and hydrochloric acid: Mg(s)+2HCl(aq)→MgCl2(aq)+H2(g)\text{Mg(s)} + 2\text{HCl(aq)} \rightarrow \text{MgCl}_2\text{(aq)} + \text{H}_2\text{(g)} Setup 1 uses 25°C and 0.50 M HCl with the same size magnesium strip as Setup 2. Setup 2 uses 25°C and 1.0 M HCl. Compared to Setup 1, what happens to the rate in Setup 2, and why?
  3. A classroom demonstration uses dry ice (solid CO2_2) in a small container to create fog. As the dry ice sublimates, very cold CO2_2 gas and some moisture collect around the container. The container must not crack from exposure to cold and must not react to form harmful products when CO2_2 dissolves in the moisture (slightly acidic). Which chemical property is needed?
  4. A small factory needs a pipe to carry a warm (about 60°C) saltwater solution that is slightly acidic. Requirements: (1) corrosion resistance is critical to prevent leaks, (2) pipe must tolerate 60°C continuously, (3) cost matters but leaks are unacceptable. Which material is the best compromise? Materials: - Carbon steel: low cost; strong; but rusts/corrodes quickly in salty, slightly acidic water. - PVC plastic: low cost; good corrosion resistance; but softens near 60–70°C and can deform over time. - Stainless steel: excellent corrosion resistance; handles 60°C; but much more expensive.
  5. A country considering nuclear energy plans to import reactor fuel and build enrichment facilities. Nuclear power could provide steady electricity with low greenhouse gas emissions during operation, but enrichment technology can also be used to produce material suitable for nuclear weapons if misused. Which option best captures this benefit-risk trade-off?
  6. Hydrogen peroxide decomposes (in the presence of a catalyst) according to: 2H2O2→2H2O+O22\text{H}_2\text{O}_2 \rightarrow 2\text{H}_2\text{O} + \text{O}_2 If you start with 5.0 mol H2O2\text{H}_2\text{O}_2, what is the maximum amount of O2\text{O}_2 that can form?
  7. Two reactant curves are shown on a concentration-versus-time graph. Both start at the same concentration. Curve M decreases quickly at first but then becomes gentle; Curve N decreases gently the entire time. Which statement best describes the rates?
  8. In the nuclear equation 92238U→90234Th+X^{238}_{92}\mathrm{U} \rightarrow ^{234}_{90}\mathrm{Th} + X, what particle is XX?
  9. A community is comparing nuclear power and coal power for a new electricity plant. They note that nuclear plants produce very low greenhouse gas emissions during operation, while coal plants release carbon dioxide and other air pollutants. However, nuclear plants create radioactive waste and require strong safety systems to prevent radiation release in accidents, while coal has ongoing air-quality and climate impacts. Which statement best evaluates the trade-offs using this information?
  10. A packaging team is choosing a material for single-use cutlery at a music festival. They compared conventional polystyrene (PS) and a compostable bioplastic labeled PLA (polylactic acid). The cutlery must last through one meal without dissolving, and the city requires that festival waste be industrially compostable. In a pilot run, PLA forks remained intact during use and, at an industrial composting facility, lost most of their mass after 10 weeks, while PS forks showed no visible change. Which justification best supports choosing PLA over PS?
  11. A cafeteria wants a countertop surface near a station where lemon juice and vinegar are used daily. Requirements: (1) must resist weak acids without staining/corroding, (2) should be easy to clean, (3) should not chip easily, and (4) budget is moderate. Which material is the best trade-off? Materials: - Marble: looks nice; but reacts with acids and can etch/stain. - Stainless steel: resists weak acids well; easy to sanitize; but can scratch and is more expensive. - Laminated wood (plastic laminate over wood): inexpensive; many colors; but can swell if water gets into seams and can be damaged by heat.
  12. A student mixes two clear solutions in a cup. The temperature drops from 26°C to 19°C. The student says, "It must be exothermic because a reaction happened right away." Which choice best corrects the student using the temperature evidence?
  13. Two solutions are mixed in an open beaker. - Solution A: 25.0 mL calcium chloride, CaCl2(aq), mass = 26.6 g, clear, 21.0°C - Solution B: 25.0 mL sodium carbonate, Na2CO3(aq), mass = 26.4 g, clear, 21.0°C After mixing and stirring for 1 minute: - Mixture: cloudy white, 28.0°C - Mass of beaker + mixture is 0.0 g different from the combined initial masses (within balance precision) Which observation is the best evidence that a new substance formed?
  14. A student mixes two liquids in a small cup at room temperature. The mixture quickly becomes noticeably colder to the touch and a strong new odor is detected that was not present in either liquid alone. What evidence indicates a chemical change occurred? (Select the best answer.)
  15. In the balanced equation Zn+2HCl→ZnCl2+H2\mathrm{Zn + 2HCl \rightarrow ZnCl_2 + H_2} how many moles of HCl\mathrm{HCl} are required to react with 11 mol of Zn\mathrm{Zn}?
  16. A piece of iron is left outside for several days. The surface changes from shiny gray to a reddish-brown coating. Which observation is evidence of a chemical reaction?
  17. A student is told that halogen reactivity changes down Group 17 because atoms lower in the group attract an extra electron less strongly. Which halogen is least reactive (based on group position) among fluorine (F, period 2), chlorine (Cl, period 3), bromine (Br, period 4), and iodine (I, period 5)?
  18. A student measured the pH after adding different volumes of 0.10 M HCl to 50.0 mL of distilled water. The pH was recorded immediately after mixing. Data: - 0.0 mL HCl: pH 6.8 - 1.0 mL HCl: pH 3.1 - 2.0 mL HCl: pH 2.8 - 3.0 mL HCl: pH 2.6 What conclusion is supported by the data?
  19. In a sealed flask, hydrogen reacts with oxygen: 2H2(g)+O2(g)→2H2O(g)2\text{H}_2(g) + \text{O}_2(g) \rightarrow 2\text{H}_2\text{O}(g). The total mass of the sealed flask and gases is 200 g before the reaction and 200 g after the reaction. What is the best conclusion?
  20. A neutral atom has 9 electrons. What is its atomic number (ZZ)?

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