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Practice Test 38 - High School Chemistry

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

  1. A student designed a small water bottle with a straw made of natural rubber because it was flexible and cheap. Testing with different drinks: - With plain water: no smell or taste after 1 day. - With lemon sports drink (acidic): after 1 day, the straw had a noticeable odor and the drink tasted slightly "rubbery." - With the same lemon drink in a silicone straw: no odor/taste change after 1 day. Which refinement is most supported by the evidence?
  2. In a classroom demo, a small piece of sodium (Na), a Group 1 element in Period 3, is stored under mineral oil. When a tiny piece is dropped into water, it reacts quickly and produces bubbles and heat. Which justification best explains why sodium must be stored under oil to prevent reaction with air and water?
  3. Beryllium (Be) has electron configuration 1s2 2s2 and magnesium (Mg) has electron configuration [Ne]3s2. Magnesium has a larger atomic radius than beryllium. Which configuration feature best explains this?
  4. A student notices that an apple slice turns brown after being left out. They want to test whether the browning is a chemical change and whether lemon juice slows the change. Which investigation design best addresses a clear, testable question with appropriate variables and evidence?
  5. A student mixes copper(II) sulfate solution (blue) with sodium carbonate solution (colorless) and sees a cloudy solid form. The student wants to confirm whether this is a chemical change and not just "undissolved powder," because the class is practicing identifying evidence of reactions. Which investigation design best confirms a chemical reaction using a comparison/control and clear evidence collection?
  6. Aluminum reacts with oxygen to form aluminum oxide: 4Al+3O2→2Al2O3\textbf{4Al} + \textbf{3O}_2 \rightarrow \textbf{2Al}_2\textbf{O}_3 If 1.5 mol1.5\ \text{mol} of Al2O3\text{Al}_2\text{O}_3 form, how many moles of Al\text{Al} were consumed?
  7. Carbon (C) has 4 valence electrons (electron configuration ends in 2s² 2p²). In many compounds, carbon forms 4 covalent bonds (for example, CH₄). How does carbon's valence electron structure relate to its bonding tendency?
  8. A neutral atom has 17 protons and 18 neutrons. What is the element?
  9. A student claims: "The reaction between calcium chloride and water is exothermic." Evidence: 1) Temperature increased from 21.0°C to 29.8°C after calcium chloride was added to water. 2) The beaker felt warm to the touch. 3) In a repeat trial with the same amounts, temperature increased from 21.2°C to 29.6°C. 4) The calcium chloride was a white solid before mixing. Is the claim supported by the evidence? Why or why not?
  10. A school lab builds a simple CO2_2 generator for a plant experiment. Design 1 uses a calcium carbonate (marble chips) + hydrochloric acid reaction inside a container sealed with a rubber stopper and a short length of natural rubber tubing to deliver gas to the plant chamber. The team chose natural rubber tubing because it is flexible and cheap. During a 30-minute test, the tubing becomes soft and slightly sticky near the container end, and a strong acidic odor is noticed near the tubing connection. CO2_2 delivery rate drops by about 40% by the end of the test. Which refinement best targets the problem shown by the evidence?
  11. Alkaline earth metals (Group 2) react with water, and their reactivity increases down the group (though less dramatically than Group 1). Compare magnesium (Mg, Period 3) and calcium (Ca, Period 4). Which is expected to react faster with cold water?
  12. Two elements are both in group 17 (halogens). Element X has electron configuration [He]2s2 2p5 and element Y has electron configuration [Ne]3s2 3p5. Based on valence electrons, why do X and Y show similar chemical behavior (such as tending to form −1-1 ions)?
  13. A lab is selecting containers for storing concentrated nitric acid (HNO3\text{HNO}_3). They chose PTFE (Teflon) bottles over aluminum bottles. In a compatibility test, aluminum samples showed surface attack and gas bubbles, while PTFE showed no visible change. Which reasoning best justifies the decision?
  14. Calcium (Ca) has atomic number 20. What is the electron configuration of a neutral calcium atom (do not go beyond 4s)?
  15. A student compared the reactivity of three metals in 1.0 M HCl. Each metal sample had a mass of 0.50 g and was placed in 20.0 mL of acid at 22.0°C. The student recorded qualitative observations and the time for visible bubbling to stop. Which statement best describes the pattern in the data?​
  16. In a sealed syringe, 10 mL of a gas-phase reactant mixture is allowed to react at constant temperature. The plunger is pushed in so the volume decreases to 5 mL, increasing the pressure, while the temperature stays the same. Assuming the reaction rate depends on collisions between gas particles, how will the reaction rate change after compressing the gas?
  17. Two curves are shown for the concentration of reactant BB versus time under two different conditions. Curve X decreases steeply at first and becomes almost flat relatively early. Curve Y decreases gently and is still noticeably sloping downward at the same later time. Which condition completes the reaction sooner (reaches a near-constant concentration sooner)? Axes: y = concentration of [B][B] (arbitrary units), x = time (s).
  18. The nuclear equation 614C→714N+−10e^{14}_{6}\text{C} \rightarrow ^{14}_{7}\text{N} + ^{0}_{-1}\text{e} shows which type of radioactive decay?
  19. A teacher demonstrates reactions of Group 1 metals with water using equal-sized pieces of lithium (Li, Group 1 Period 2), sodium (Na, Group 1 Period 3), and potassium (K, Group 1 Period 4). Which order correctly lists them from least vigorous to most vigorous reaction with water?
  20. Which element (atomic numbers 1-20) has the electron configuration 1s² 2s² 2p⁶ 3s² 3p²?

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