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Practice Test 22 - High School Chemistry

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

  1. Two alkaline earth metals—magnesium (Mg, Group 2 Period 3) and calcium (Ca, Group 2 Period 4)—are placed in separate containers of water at the same temperature. Which metal is expected to react faster with water?
  2. A class tests: "How does the amount of solute affect the final pH of a dilute acid solution?" They prepare three beakers, each containing 100.0 mL of 0.10 M acetic acid at 25°C. They add solid sodium acetate to each beaker in different masses (0.50 g, 1.00 g, and 1.50 g), stir for 2 minutes, and then measure pH with the same calibrated pH probe. Identify the independent, dependent, and controlled variables for this investigation.
  3. Many homes use smoke detectors that contain a tiny amount of americium-241, a radioactive material that helps detect smoke. The benefit is early warning in a fire, but there are concerns about proper disposal so the radioactive source does not end up in the environment or get mishandled. Which choice is the most balanced assessment?
  4. A student adds yeast to warm sugar water in a bottle and stretches a balloon over the opening. After 15 minutes, the balloon begins to inflate. The student claims this proves a chemical change occurred (fermentation producing a gas). The teacher wants an investigation design that confirms the gas production is due to a chemical reaction and not just trapped air expanding. Which plan is best?
  5. An ion has 9 protons and 10 electrons. What is the charge on the ion?
  6. Consider the balanced equation: 2H2+O2→2H2O2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O} If 5.0 mol5.0\ \text{mol} of H2\text{H}_2 react completely, how many moles of H2O\text{H}_2\text{O} are produced?
  7. Consider the reaction H2+Cl2→2HCl\text{H}_2 + \text{Cl}_2 \rightarrow 2\text{HCl}. During the reaction, H–H and Cl–Cl bonds are broken and H–Cl bonds are formed. Which statement correctly describes the energy changes during bond breaking and bond forming?
  8. Consider the balanced equation: 2H2+O2→2H2O\textbf{2H}_2 + \textbf{O}_2 \rightarrow \textbf{2H}_2\textbf{O} If 5.0 mol5.0\ \text{mol} of O2\text{O}_2 react completely, how many moles of H2O\text{H}_2\text{O} are produced?
  9. Consider the balanced equation: 2H2O2→2H2O+O22H_2O_2 \rightarrow 2H_2O + O_2 If 6.0 mol6.0 \text{ mol} of H2OH_2O form, how many moles of O2O_2 form?
  10. Oxygen (O, atomic number 8) commonly forms the oxide ion O. Which statement correctly describes what happens to electrons when O becomes O and why?
  11. A student investigates the question: How does light intensity affect the rate of a photochemical reaction? (high school simulation using light-sensitive beads in a dilute dye solution). She places identical beakers containing 100 mL of the same dye solution under a lamp at distances of 10 cm, 20 cm, 30 cm, and 40 cm. She keeps exposure time the same (5.0 minutes) and uses the same type and number of beads in each beaker. After 5.0 minutes, she compares the color change by measuring absorbance with the same colorimeter setting. What is being measured as the outcome (dependent variable)?
  12. A student reads: "Chemical bond energies are typically a few eV per bond, while nuclear reaction energies are typically a few MeV per event." Which statement best interprets what this means for comparing everyday burning (chemical) to radioactive decay or fission (nuclear)?​
  13. A reaction has ΔH=−5 kJ\Delta H = -5\ \mathrm{kJ}. Which statement is correct about the heat flow for the reaction (as written)?
  14. Two clear liquids are mixed in a beaker: 30 mL of Liquid X (clear, colorless) and 30 mL of Liquid Y (clear, colorless). Immediately after mixing, the beaker becomes warm and the liquid turns pale yellow. No bubbles appear and no solid forms. Data: - Temperature before mixing: 20.0°C - Temperature 30 seconds after mixing: 28.0°C - Temperature 5 minutes after mixing: 21.0°C - When the mixture is poured through filter paper, nothing is collected. Based on the evidence, did a chemical reaction occur? Choose the best CER justification.
  15. A piece of paper is cut into many small strips with scissors. Before, it is one sheet; after, it is several smaller pieces of paper. What kind of change occurs?
  16. A student reacts identical 2 cm strips of magnesium ribbon with 25 mL of 1.0 M HCl. The only change is the temperature of the acid. Which statement best explains why the reaction is faster in Trial 2?
    TrialTemperature of HCl (°C)ObservationTime for Mg to disappear
    120steady bubbling60 s
    240vigorous bubbling15 s
  17. Element A is sodium (Na) with electron configuration [Ne]3s1[Ne]3s^1, and element B is potassium (K) with electron configuration [Ar]4s1[Ar]4s^1. Potassium has a lower first ionization energy than sodium. Which electron-configuration-based reason best explains why K's outer electron is easier to remove than Na's?
  18. Consider atomic size in period 2 using these electron configurations: carbon (C) [He]2s2 2p2 and oxygen (O) [He]2s2 2p4. Oxygen has a smaller atomic radius than carbon. Which statement best explains this using effective nuclear charge ideas?
  19. Two different bonds are compared: one is described as stronger and one as weaker. Which statement correctly relates bond strength to energy in bond breaking and bond forming?
  20. For a reaction at constant pressure, ΔH\Delta H is defined as ΔH=H(products)−H(reactants)\Delta H = H(\text{products}) - H(\text{reactants}). If ΔH=−30 kJ\Delta H = -30\ \text{kJ}, which statement must be true?

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