Practice Test 44 - 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 student claims that dissolving table salt (NaCl) in water is a chemical change because "the salt disappears." The teacher asks the class to design an investigation to test the claim using safe, common lab tools (beakers, balance, hot plate, thermometer). Which investigation design best tests whether dissolving NaCl in water is a chemical change or a physical change? Your design should include a comparison/control and specify the evidence to collect.
2. A class designs a container to mix and store a basic cleaning solution (contains sodium hydroxide, pH ≈ 13). Initial design: a glass jar with a metal (steel) lid was chosen because glass is chemically resistant and transparent. Test evidence (3-week use): the glass remains clear, but the lid develops rust and becomes difficult to open; brown residue appears around the lid threads. The solution itself still cleans well. Which refinement best addresses the failure shown by the evidence while keeping the benefits of the original design?
3. Iron wool rusts over several days in a dish left in open air: 4Fe(s) + 3O$_2$(g) → 2Fe$_2$O$_3$(s). Measurements: - Mass of iron wool at start: 20 g - Mass of rusted iron wool later: 26 g Which explanation best accounts for the increase?
4. Magnesium (Mg) is a Group 2 element with atomic number 12. It commonly forms Mg²⁺. Which explanation best describes how Mg²⁺ forms from a neutral Mg atom?
5. A student claims: "A precipitate formed because a chemical reaction occurred when two clear solutions were mixed." Evidence: 1) The mixture turned cloudy and a white solid appeared within 10 seconds. 2) After filtering, the solid remained on the filter paper and did not dissolve when rinsed with water. 3) The total volume of liquid in the beaker increased by 2 mL because the student added extra water. 4) The room lights were turned off during one trial. Which piece of evidence does NOT support the claim?
6. Displacement reaction (halogens): Iodine (I$_2$, Group 17 Period 5) is added to a solution of potassium chloride (KCl). Will iodine displace chlorine from chloride ions?
7. Magnesium-24 is written as $^{24}\text{Mg}$. A magnesium ion $\text{Mg}^{2+}$ forms when magnesium loses 2 electrons. How many protons, neutrons, and electrons does $^{24}\text{Mg}^{2+}$ have?
8. A student compares the same gas-producing reaction in two setups: Setup 1 (open cup): Total mass before = 90 g; total mass after = 86 g. Setup 2 (sealed bag): Total mass before = 90 g; total mass after = 90 g. Which statement best explains the difference?
9. A student team designs a reusable spray bottle for a citrus-based degreaser (contains d-limonene and other organic solvents). Initial design: a clear polycarbonate (PC) bottle was chosen because it is impact-resistant and transparent. Test evidence (2-week use test): the bottle developed fine cracks around the neck and trigger threads, and a faint solvent smell was noticed outside the bottle even when closed. Mass of the filled bottle decreased by 1.8% over 14 days at room temperature. The trigger still works and the bottle does not shatter. Based on the evidence, which refinement would best address the failure mode while keeping the bottle reusable?
10. A student investigated how surface area affects reaction rate. Equal masses of calcium carbonate were reacted with the same acid under the same conditions: $1.00\,\text{g}$ CaCO$_3$, $50.0\,\text{mL}$ of $1.0\,\text{M}$ HCl, and $23.0^\circ\text{C}$. The student recorded the time until fizzing stopped.

    CaCO$_3$ form	Time until fizzing stopped (s)	Observation
    large chips	95	gentle bubbling
    small chips	62	steady bubbling
    powder	28	vigorous bubbling

    What relationship do the data reveal between surface area and reaction time?
11. A metal handrail outside a school is near the ocean and gets frequent salt spray, rain, and humid air. The current finish is failing and rust spots are appearing. The replacement coating must protect the metal for years without producing toxic fumes during normal outdoor use. Which chemical properties are most important for the coating?
12. Aluminum (Al) is in Group 13 with 3 valence electrons (ends in 3s² 3p¹). Aluminum often forms Al³⁺ in ionic compounds. Which explanation best connects its valence electrons to this ion formation?
13. Which set of coefficients balances the combustion reaction using the smallest whole numbers? C3H8 + O2 → CO2 + H2O
14. Iron(III) oxide forms by the reaction $\,4Fe + 3O_2 \rightarrow 2Fe_2O_3\,$. If you have 8.0 mol $Fe$ and 5.0 mol $O_2$, which reactant is the limiting reactant?
15. Aluminum chloride forms by $\,2\text{Al} + 3\text{Cl}_2 \rightarrow 2\text{AlCl}_3\,$. If you have $4.0\ \text{mol Al}$ and $3.0\ \text{mol Cl}_2$, which reactant is limiting?
16. Carbon dioxide forms by combustion: $\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}.$ If you have $4.0\ \text{mol}$ of $\text{CH}_4$ and $6.0\ \text{mol}$ of $\text{O}_2$, what is the maximum amount of $\text{CO}_2$ that can form (in moles)?
17. Sodium (Na) is in group 1 and has electron configuration $1s^2\,2s^2\,2p^6\,3s^1$. A small piece of sodium reacts vigorously with water and forms Na\u207a ions. How does sodium's atomic structure explain this chemical behavior?​
18. Hydrogen peroxide decomposes as $2\text{H}_2\text{O}_2 \rightarrow 2\text{H}_2\text{O} + \text{O}_2.$ Which statement correctly compares moles of $\text{H}_2\text{O}_2$ reacted to moles of $\text{O}_2$ formed?
19. An instant cold pack is activated by breaking an inner pouch so the chemicals mix. The pack's temperature drops from $24^\circ\text{C}$ to $10^\circ\text{C}$ within a minute and feels cold to the touch. Which statement best classifies this process?
20. A country considering nuclear power notes that the same general nuclear knowledge base can be connected to weapons development if fissile materials are diverted. Benefits of nuclear power include large-scale electricity generation with low operational greenhouse gas emissions. Risks include long-lived waste, accident potential, and proliferation concerns. Which option shows the most balanced evaluation?

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