Practice Test 40 - 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 lunch container is being designed specifically for acidic foods such as tomato sauce and orange slices (typical pH around 3–4). The container will be used repeatedly and washed in warm water. Which chemical properties are the most important criteria for the container material?
2. Silicon has electron configuration [Ne]3s2 3p2 and phosphorus has electron configuration [Ne]3s2 3p3. Phosphorus has a higher first ionization energy than silicon. Which explanation best uses electron configuration to explain the increase across the period?
3. A student reacts calcium carbonate (CaCO$_3$) with the same volume and concentration of vinegar at the same temperature. The student uses the same mass of CaCO$_3$ each time but changes the form of the solid.

   Trial	Form of CaCO$_3$	Observation	Time for fizzing to mostly stop
   1	large chips	gentle fizzing	120 s
   2	small chips	faster fizzing	40 s
   3	powder	very rapid fizzing	10 s

   Which is the best explanation for why Trial 3 is fastest?
4. A sodium atom (Na) has atomic number 11 and a valence electron configuration ending in $3s^1$. It commonly forms the ion Na⁺. Which explanation best describes how a neutral Na atom becomes Na⁺ and why the +1 charge is favored?
5. A hospital selected titanium for bone screws rather than plain carbon steel. The screws will remain in the body for years and contact salty body fluids. In accelerated testing in saline at body temperature, carbon steel samples showed rapid rusting and mass loss, while titanium samples showed no visible corrosion. Which justification best supports titanium as the better choice?
6. Use the periodic trend for metallic character. The following elements are all in period 3: - Na (group 1) - Si (group 14) - S (group 16) Which element has the least metallic character?
7. A calcium ion is written as Ca²⁺. What is the full electron configuration of Ca²⁺? (Calcium has atomic number 20.)
8. A school wants to store a concentrated cleaning solution that contains ammonia and has a strong odor. The container should minimize odor leakage, be chemically compatible (no cracking or reaction), and be safe for students to handle. Cost is important, but leaks/odor are a major problem. Which material is the best trade-off? Options: - HDPE plastic: good chemical resistance; low cost; can allow more odor permeation than some materials. - Glass: very low permeability (good odor barrier); chemically inert; heavy and can break. - Thin PET plastic: clear and cheap; can stress-crack with some cleaners; moderate odor barrier.
9. In a single-step energy profile, which vertical difference corresponds to the overall energy change ($\Delta H$)?
10. A food company needs a container for packaging a hot, acidic tomato sauce (pH ~4) filled at 90°C. Requirements: food-safe (non-toxic) is critical, must tolerate 90°C during filling, and should minimize chemical interaction with the acidic sauce. Cost matters but is secondary to safety and performance. Which material is the best trade-off? Options: - PET plastic: inexpensive and clear; can soften/warp near 90°C; generally food-safe. - Glass jar: chemically inert and food-safe; handles 90°C; heavier and breakable; moderate cost. - Aluminum can (unlined): lightweight and cheap; acidic foods can corrode aluminum and affect taste/safety.
11. In the nuclear equation $^{238}_{92}\text{U} \rightarrow ^{234}_{90}\text{Th} + X,$ what is particle $X$?
12. Sodium (Na), magnesium (Mg), and aluminum (Al) are all in Period 3. Their valence electrons are 1 (Na), 2 (Mg), and 3 (Al). Sodium is more reactive than magnesium, and magnesium is generally more reactive than aluminum. Which explanation best connects this trend to atomic structure?
13. A student drops a piece of dry ice (solid carbon dioxide, $\text{CO}_2(s)$) into a beaker of room-temperature water. Observations and data: - A thick white fog forms above the beaker - Many bubbles rise from the dry ice - The dry ice piece gets smaller and eventually disappears - Temperature of the water drops from $22.0^\circ\text{C}$ to $16.0^\circ\text{C}$ - The water remains liquid and clear Based on the evidence, did a chemical reaction occur? Choose the best CER justification.
14. A company tested two coatings for a cast-iron outdoor grill grate: (1) a ceramic-based coating and (2) a standard paint not rated for high heat. The ceramic-coated grate was heated to $450\,^{\circ}\mathrm{C}$ for 50 cycles and showed no peeling and no detectable coating chemicals in a wipe test. The painted grate smoked, blistered, and flaked after 5 cycles. Which justification best supports choosing the ceramic coating for the final product?
15. Melting ice can be written as: $\text{H}_2\text{O}(s) \rightarrow \text{H}_2\text{O}(l) \quad \Delta H = +6.0\ \text{kJ/mol}$ Which statement best describes what this means?
16. A student tested whether a precipitate forms when mixing aqueous solutions of sodium sulfate (Na$_2$SO$_4$) and barium chloride (BaCl$_2$). Each trial mixed 10.0 mL of 0.10 M Na$_2$SO$_4$ with different volumes of 0.10 M BaCl$_2$, then added water to keep the total volume at 30.0 mL. The student recorded the mixture appearance after 1 minute. What trend is visible in the data?
17. A hospital wants to expand its use of PET scans, which use short-lived radioactive tracers to help detect cancer and monitor organ function. PET scans can improve diagnosis and treatment planning, but they involve radiation exposure (though typically controlled and limited) and require safe handling and disposal of radioactive materials. Which statement best balances benefits and risks?
18. A shiny iron nail is left outdoors for several days after a rain. Over time, the nail's surface changes from metallic gray to a rough reddish-brown coating. Which change provides evidence of a chemical reaction?
19. A reaction is carried out in a sealed flask: $\text{A}(aq) + \text{B}(aq) \rightarrow \text{C}(aq)$ Mass of A solution added: 18 g Mass of B solution added: 7 g After the reaction, the flask contains only solution C (no gas formed) and remains sealed. What should be the mass of solution C inside the flask (ignoring the flask's mass)?
20. A strip of metal is placed into a blue solution. After several minutes, the blue color fades noticeably and a reddish-brown coating appears on the metal. Which combination of observations supports the claim that a chemical reaction occurred?

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