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Practice Test 50 - High School Chemistry

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

  1. Element A is sodium (Na), a period 3, group 1 element with electron configuration [Ne]3s1. Element B is potassium (K), a period 4, group 1 element with electron configuration [Ar]4s1. Potassium has a larger atomic radius than sodium. Which electron-configuration feature best explains why?
  2. A student mixes two solutions and filters the mixture. Before mixing: - 40.0 mL silver nitrate solution, AgNO3(aq): mass = 41.2 g, clear/colorless, 23.0°C - 40.0 mL sodium chloride solution, NaCl(aq): mass = 40.8 g, clear/colorless, 23.0°C After mixing (in a beaker): - Mixture appearance: cloudy; a white solid forms - Temperature: 23.0°C - Mass of dried solid collected after filtering: 2.6 g Which data point is the strongest evidence that a chemical reaction occurred?
  3. Bromine (Br, atomic number 35) is a group 17 nonmetal and commonly forms Br. Which reasoning best explains why Br forms a -1 ion?
  4. A displacement test is attempted by adding iodine (I2_2, Group 17, Period 5) to a solution of potassium chloride (KCl). Based on periodic trends for Group 17, will iodine displace chlorine from chloride ions?
  5. Calcium (Ca) is a Group 2 element with atomic number 20. When it forms its common ion, which change occurs and why?
  6. Ammonia reacts with oxygen (simplified) as: 4NH3+5O2→4NO+6H2O4\text{NH}_3 + 5\text{O}_2 \rightarrow 4\text{NO} + 6\text{H}_2\text{O} If 4.0 mol NH3\text{NH}_3 and 4.0 mol O2\text{O}_2 are mixed, which reactant is limiting?
  7. Alkali metal reactivity increases down Group 1. A teacher compares sodium (Na, Period 3) and rubidium (Rb, Period 5) in separate water demonstrations. Which prediction is most accurate?
  8. A student investigated how temperature affects the rate of reaction between magnesium ribbon and 1.0 M HCl. For each condition, 0.50 g of Mg was added to 50.0 mL of acid, and the time for bubbling to stop was recorded. Data: - 20.0°C: 126 s - 30.0°C: 84 s - 40.0°C: 55 s - 50.0°C: 38 s What trend is visible in the data?
  9. A strip of zinc metal is placed into a blue solution in a clear cup. After several minutes, the blue color fades, and a reddish coating appears on the zinc strip. Which combination of observations supports the claim that a chemical reaction occurred?
  10. A class designed a clear plastic container to store a citrus-based degreaser (contains d-limonene). They chose polystyrene because it was clear and rigid. In a 7-day compatibility test, the container walls became cloudy and soft, and the lid threads warped, causing leaks when tipped. Which refinement is most evidence-based and likely to prevent the observed degradation?
  11. Sodium (Na) is in group 1 and has 1 valence electron. In reactions, sodium commonly forms the ion Na⁺. How does sodium's atomic structure explain this behavior?
  12. Use the periodic trend for atomic radius. The elements below are all in period 3: - Na (group 1) - Al (group 13) - Cl (group 17) Which element has the smallest atomic radius?
  13. A student compares the first ionization energies of sodium (Na) and chlorine (Cl), both in period 3. Data from a reference table shows Na has a much lower first ionization energy than Cl. Which reasoning best justifies this difference using electron configuration and periodic trends across a period?
  14. Which full electron configuration correctly represents fluorine (F), atomic number 9?
  15. Three alkali metals—lithium (Li, Group 1 Period 2), sodium (Na, Group 1 Period 3), and potassium (K, Group 1 Period 4)—are each dropped into separate beakers of cold water. Which metal reacts most vigorously with the water?
  16. In a reaction, two different molecules must collide in a specific way for new bonds to form. A student asks why the molecules can collide many times without reacting. Which response best uses collision theory to answer the student?
  17. Copper (Cu) is commonly used for electrical wiring in homes. Using copper's periodic-table classification as a metal and basic atomic structure ideas, which justification best explains why copper is a good conductor of electricity?
  18. In the nuclear equation 84210Po→82206Pb+X,^{210}_{84}\text{Po} \rightarrow {}^{206}_{82}\text{Pb} + X, what is XX?
  19. Scientists use carbon-14 dating to estimate the age of once-living materials (like wood or bone), which helps archaeology and history. The benefit is improved understanding of past events. A concern is that carbon-14 is radioactive, so labs must follow safety procedures and prevent contamination, even though the amounts used are typically small. Which option best evaluates this use of nuclear processes?
  20. To answer the question, How does stirring affect the dissolving rate of salt in water?, students add 5.0 g of table salt (NaCl) to 100 mL of water at 25°C in identical beakers. Trial 1 is not stirred. Trial 2 is stirred at 1 rotation per second. Trial 3 is stirred at 2 rotations per second. The same thermometer is used to confirm the water stays at 25°C, and the student records how many seconds it takes until the solution looks clear with no visible crystals. Which factor is the independent variable?

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