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Practice Test 45 - High School Chemistry

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

  1. Potassium has electron configuration [Ar]4s1 and sodium has electron configuration [Ne]3s1. Potassium has a lower first ionization energy than sodium. Which explanation using electron configuration is best?
  2. The fluoride ion, F⁻, forms when fluorine (atomic number 9) gains one electron. What is the electron configuration of F⁻?​
  3. A student adds 5.0 g of table salt (NaCl) to 100 mL of water in a beaker and stirs for 2 minutes. Observations/data: - Salt crystals disappear and the liquid stays clear - Temperature changes from 21.0∘C21.0^\circ\text{C} to 20.2∘C20.2^\circ\text{C} - No bubbling and no odor - When the solution is left in a shallow dish overnight, water evaporates and white salt crystals are found again Based on the evidence, did a chemical reaction occur? Choose the best CER justification.
  4. Carbon (C), oxygen (O), and fluorine (F) are all in period 2 (groups 14, 16, and 17 respectively). Which element has the highest first ionization energy?
  5. Compare the first ionization energies of sodium and potassium using their electron configurations: Na: [Ne]3s1 (period 3) and K: [Ar]4s1 (period 4). Potassium has a lower first ionization energy than sodium. Which statement best explains this using shielding and distance of the valence electron?
  6. Arrange these Group 2 metals in order of decreasing reactivity with water, based on periodic position: Ba (barium, Group 2 Period 6), Ca (calcium, Group 2 Period 4), Mg (magnesium, Group 2 Period 3).
  7. A student is designing a small storage box for collecting used household batteries for recycling. Some batteries may leak, releasing corrosive electrolytes. The box must resist chemical attack from leaked contents, must not produce dangerous reactions (like heat or gas) if leakage occurs, and must be safe to handle indoors. Which chemical properties should the designer require for the box material?
  8. A student dissolves table salt (NaCl(s)) in water. Before: - Water: 50.0 g, 22.0°C, clear liquid - Salt: 5.0 g, white solid - Total mass: 55.0 g After stirring (no heating): - Saltwater solution: 55.0 g, 22.0°C, clear/colorless (no solid visible) What does the data indicate?
  9. A student investigates: How does the presence of a catalyst affect the decomposition of hydrogen peroxide? Two 250 mL flasks each receive 30.0 mL of 3% H2_2O2_2 at 25C. Flask 1 receives 0.50 g of MnO2_2 powder, and Flask 2 receives no MnO2_2. Each flask is connected to a gas syringe, and the student records the volume of oxygen gas collected every 10 seconds for 1 minute. What is being deliberately changed between the two setups?
  10. An ice cube is left on a plate at room temperature. Before, it is solid ice; after 10 minutes, there is a puddle of liquid water on the plate. What kind of change occurred?
  11. A student claims that dissolving table salt (NaCl) in water is a chemical change because the salt "disappears." Design an investigation to test this claim using observable evidence. Which design best distinguishes a physical change from a chemical reaction?
  12. A student has three bottles of halogens (Group 17): chlorine (Cl, period 3), bromine (Br, period 4), and iodine (I, period 5). Halogen reactivity depends on periodic position. Arrange these halogens from most reactive to least reactive.
  13. Arrange these halogens in order of increasing reactivity (least to most), based on periodic position: F (fluorine, Group 17 Period 2), Cl (chlorine, Group 17 Period 3), Br (bromine, Group 17 Period 4).
  14. A student heats a small amount of a blue solid in an evaporating dish. The solid melts into a blue liquid. After cooling, it becomes a blue solid again with the same appearance. The mass before heating is 4.50 g and after cooling is 4.50 g. No gas or odor is noticed. Did a chemical reaction occur during heating? Choose the best CER justification.
  15. What coefficients balance the equation using the smallest whole numbers? KClO3 → KCl + O2
  16. Which electron configuration correctly represents a neutral aluminum atom (Al, atomic number 13)?
  17. A lab must store 6 M hydrochloric acid (HCl) for student experiments. The storage container must not react with the acid, must not contaminate it, and must remain safe if dropped. The lab chose a HDPE (high-density polyethylene) bottle instead of a glass bottle. Which reasoning best justifies this design decision using chemical properties and safety trade-offs?
  18. A student compares how vigorously strontium (Sr, Group 2 Period 5) and magnesium (Mg, Group 2 Period 3) react with water. Which prediction is most accurate based on periodic position?
  19. Water forms by the reaction  2H2+O2→2H2O \,2H_2 + O_2 \rightarrow 2H_2O\,. If 5.0 mol H2H_2 and 2.0 mol O2O_2 are available, which statement is correct?
  20. A sugar cube is stirred into a cup of hot tea. The sugar cube disappears, and the tea tastes sweet, but no bubbles or solids form. Which best describes the change?

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