Practice Test 35 - High School Chemistry

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

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1. In a biology lab, students disinfect benches using a dilute bleach solution. The class needs a reusable spray bottle that will hold the bleach for weeks without cracking, weakening, or producing irritating gases. Based on this use, what chemical property is essential for the bottle material?
2. A student opens a bottle of carbonated water. Bubbles rapidly rise through the liquid and a hissing sound is heard. Which observation is NOT good evidence of a chemical reaction?
3. A lab has three halogens available: chlorine (Cl, Group 17 Period 3), bromine (Br, Group 17 Period 4), and iodine (I, Group 17 Period 5). If each is tested separately for reactivity as a nonmetal (tendency to gain an electron), which halogen is expected to be most reactive?
4. Magnesium has atomic number 12. When magnesium forms Mg²⁺, which electron configuration represents Mg²⁺?
5. A lab report claims: "Zinc is more reactive than copper in hydrochloric acid." Both metals were tested in separate beakers containing 50.0 mL of 1.0 M HCl at $25.0^\circ\text{C}$. Evidence: 1) Zinc produced many bubbles immediately and the metal surface visibly corroded. 2) Copper produced no visible bubbles after 5 minutes. 3) The zinc strip was dull gray, and the copper strip was shiny reddish-brown. 4) Both beakers were the same size. Which evidence is most directly relevant to comparing reactivity in acid?
6. A class investigates: How does water temperature affect how fast sugar dissolves? For each trial, a student measures 100 mL of water into the same type of glass beaker and adjusts the water to 20°C, 40°C, or 60°C using a hot plate and thermometer. Once the temperature is reached, the student adds 10.0 g of granulated sugar and stirs at a steady rate (one круг per second) with the same stirring rod. The student records the time until no solid sugar is visible. What is being measured as the dependent variable?
7. Which description best matches fusion rather than fission or radioactive decay?
8. A student mixes hydrogen peroxide solution (3% H$_2$O$_2$, the kind sold at pharmacies) with a small amount of yeast in a flask and observes foaming. They think the foam might just be trapped air from stirring (physical) rather than a chemical change. The teacher asks for an investigation design that can confirm whether a chemical reaction occurred. Which design best provides observable evidence? Assume standard lab safety and small quantities.
9. Lithium (Li) has electron configuration $1s^2\,2s^1$ and sodium (Na) has electron configuration $[Ne]3s^1$. Sodium is more reactive than lithium as a metal (it loses its outer electron more easily). Which electron-configuration-based reason best explains this?
10. A student claims: "Copper metal reacts with dilute hydrochloric acid to produce hydrogen gas." The student places a clean copper strip into 50 mL of 1.0 M HCl at 25°C and observes: 1) No bubbles are seen after 10 minutes. 2) The copper strip remains shiny and appears unchanged. 3) The temperature stays at 25.0°C. 4) The hydrochloric acid has a strong smell. Is the claim supported by the evidence? Choose the best evaluation.
11. Melting ice is represented as: $\mathrm{H_2O(s) \rightarrow H_2O(l)}$ $\Delta H = +6.0\ \mathrm{kJ/mol}$ Which interpretation is correct?
12. Electrolysis can split water: $2\text{H}_2\text{O} \rightarrow 2\text{H}_2 + \text{O}_2$. This process requires an external energy source (electricity). Which best explains why energy must be supplied in terms of bonds?
13. A student is cleaning a penny and notices it becomes shinier after soaking in vinegar and salt solution. The student wants to know whether the cleaning involves a chemical change (important for understanding corrosion) or just removal of dirt. Which investigation design best tests: Does the vinegar–salt solution chemically change the copper surface?
14. A strip of shiny gray steel wool is held with tongs over a flame for a short time. It begins to glow, gives off bright sparks, and afterward the steel wool looks darker and more brittle. Which combination of observations best supports the claim that a chemical reaction occurred?
15. A student tested how the amount of copper(II) sulfate added affects solution color intensity. In each condition, CuSO$_4$(s) was dissolved in 100.0 mL of water at 23.0°C. After dissolving, the student compared color intensity visually. Data table: - Mass CuSO$_4$ added (g): 0.50, 1.00, 1.50, 2.00 - Observation (color): light blue, medium blue, dark blue, very dark blue Which statement best describes the pattern in the observations?
16. A clear food wrap is made from a low-cost plastic film. In taste tests, crackers stored in the wrap for 48 hours develop a noticeable "plastic" odor and taste, even though the wrap prevents moisture loss well. A different wrap with a thin polyethylene (PE) inner layer shows no odor transfer while keeping similar moisture protection. What refinement best addresses the problem indicated by the evidence while preserving the good moisture barrier performance?
17. In the balanced equation $\mathrm{2KClO_3 \rightarrow 2KCl + 3O_2},$ what is the mole ratio of $\mathrm{KClO_3}$ to $\mathrm{O_2}$?
18. A student notices that steel wool left near a sink turns reddish-brown over several days. The student wonders if humidity affects how fast rust forms (a chemical change), which matters for storing tools safely. Design an investigation to answer: Does the amount of water exposure change the rate of rusting? Which plan best uses variables, controls, and measurable evidence?
19. A student pours a small amount of vinegar into a cup containing baking soda. During mixing, the mixture foams with many bubbles and the cup feels cooler to the touch afterward. Which observations provide evidence that a chemical reaction occurred?
20. How many electrons are in the outermost shell of phosphorus (P), atomic number 15?

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