Practice Test 9 - High School Chemistry

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

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1. Students design a metal coating for an outdoor handrail near the ocean. Design 1 uses a standard acrylic paint over bare steel because it is easy to apply. After 8 weeks of outdoor exposure, the paint looks fine on the top surfaces, but blistering and rust appear mainly on the underside and in crevices where salty water collects. Which refinement most directly addresses the failure mode indicated by the evidence?
2. In a lab, a small piece of sodium (Na), located in Group 1 and Period 3, is kept under mineral oil because it quickly reacts with moist air and can react violently with water. Which justification best explains why sodium must be stored this way using periodic trends and atomic structure?
3. To answer How does the concentration of a salt solution affect electrical conductivity?, students prepare three NaCl(aq) solutions: 0.10 M, 0.50 M, and 1.0 M. They pour 75.0 mL of each solution into identical beakers at 22C and use the same conductivity probe each time. Before each reading, they rinse the probe with distilled water and blot it dry. They record the conductivity value displayed by the meter. Which is the independent variable?
4. A student says, "If I just burn enough gasoline, I can match the energy of a nuclear reaction." Which response best addresses the misconception while keeping the comparison per atom?
5. A disposable hand warmer is opened and shaken. Over the next few minutes, its temperature rises from 21°C to 38°C without any external heating and it feels warm in the student's hand. Which statement best classifies this process?
6. Magnesium burns in air: $2\text{Mg}(s) + \text{O}_2(g) \rightarrow 2\text{MgO}(s)$. A strip of magnesium has a mass of 10 g before burning. After burning in an open crucible, the magnesium oxide ash has a mass of 16 g. Which explanation best accounts for the mass increase?
7. A student bends a copper wire into a spiral. Before, it is a straight copper wire; after, it is the same wire in a spiral shape with the same color and mass. What kind of change occurs?
8. Two gases that react are placed in a sealed container. In Trial A, the gases are at lower pressure (fewer gas particles in the same volume). In Trial B, the gases are compressed to higher pressure (more particles in the same volume). The reaction happens faster in Trial B. Which collision-theory explanation best fits?
9. A company claims: "Our new cleaner chemically removes rust from iron." Evidence provided: 1) Before/after photos show a rusty nail looks shiny after soaking for 10 minutes. 2) A customer testimonial says, "It worked instantly!" 3) In a class test, the mass of a rusty nail decreases from 5.20 g to 5.05 g after soaking and rinsing. 4) The cleaner has a lemon scent. Which evidence is strongest and most relevant for supporting the claim that a chemical change (rust removal) occurred?
10. Which statement best explains why nuclear reactions generally release much more energy than chemical reactions?
11. A student mixes two aqueous solutions at room temperature.

    Property	Solution 1: AgNO3(aq)	Solution 2: NaCl(aq)	After mixing
    Volume	30.0 mL	30.0 mL	60.0 mL
    Temperature	20.0°C	20.0°C	20.5°C
    Appearance	clear	clear	cloudy; white solid appears

    Which data pattern best supports that a chemical reaction occurred?
12. Water is heated in an open pot on a stove. Before, the water is a liquid; after a few minutes, steam rises and the liquid level slowly decreases. Which type of change is described?
13. In a nuclear power plant, a uranium nucleus absorbs a neutron and then splits into two smaller nuclei, releasing additional neutrons and a large amount of energy. Which type of nuclear process is described?
14. Water forms by $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}.$ If you start with 10.0 mol $\text{H}_2$ and 3.0 mol $\text{O}_2$, which reactant is in excess after the reaction stops?
15. Carbon-14 changes into nitrogen-14 by emitting a beta particle (an electron). What type of nuclear process is this?
16. Use the periodic trend for metallic character. Compare these elements in group 2: - Be (period 2) - Mg (period 3) - Ba (period 6) Which element has the greatest metallic character?
17. A food company proposes using food irradiation to reduce bacteria in packaged spinach and extend shelf life. The process can lower the risk of foodborne illness without adding chemical preservatives. However, it requires regulated radiation sources, trained operators, and public trust; mistakes in handling the source could expose workers to radiation. Which statement best evaluates this technology?
18. Oxygen (O) is in group 16 and has 6 valence electrons (electron configuration ends in 2s² 2p⁴). Oxygen often forms two bonds in covalent molecules (for example, H₂O). Why does oxygen typically form 2 bonds?
19. Determine the correct coefficients to balance the equation (smallest whole numbers): Zn + HCl → ZnCl2 + H2
20. A teacher wants a transparent container for a classroom demonstration showing a reaction that produces hot water vapor (about 90°C) and mild acidic fumes. Requirements: see-through (critical), withstand ~90°C without deforming (critical), and reasonably safe if accidentally knocked (important). Options: - Borosilicate glass: transparent; excellent heat resistance; can shatter if dropped. - Acrylic plastic: transparent; tough; can soften/warp near 90°C; may craze with some chemicals. - Polycarbonate plastic: transparent; very impact-resistant; better heat resistance than acrylic but can scratch and is more expensive. Which option is the best trade-off?

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