Free AP Chemistry Exam Question and Answers โ Questions and Answers
Question 1: To produce 127 g of copper, how many moles of electrons must be transferred?
- one mole of electrons
- two mole of electrons (Correct answer)
- three mole of electrons
- four mole of electrons
Correct answer: two mole of electrons
To produce 127 g of copper, we first determine the number of moles of copper. Given copper's molar mass is approximately 63.5 g/mol, 127 g of copper corresponds to 2 moles (127 g / 63.5 g/mol). If the copper is being reduced from a Cuโบ ion (cuprous ion), then each mole of copper requires 1 mole of electrons (Cuโบ + eโป โ Cu). Therefore, 2 moles of Cu would require 2 moles of electrons.
Question 2: The electronegativity of nitrogen is comparable to that of phosphorus and oxygen. Which of the following best sums up how the three values relate to one another?
- The value for nitrogen is higher than that for oxygen because nitrogen has more valence electrons than phosphorus, but it is lower than that for phosphorus because nitrogen has fewer protons.
- The value for nitrogen is higher than that for oxygen due to nitrogen's higher effective nuclear charge, but lower than that for phosphorus due to nitrogen's larger size.
- The value for nitrogen is less than that for oxygen because nitrogen has a lower effective nuclear charge, but it is higher than that for phosphorus since nitrogen is smaller. (Correct answer)
- Because nitrogen possesses fewer electrons than phosphorus but fewer than oxygen due to nitrogen's smaller size, the value for nitrogen is bigger than that for phosphorus.
Correct answer: The value for nitrogen is less than that for oxygen because nitrogen has a lower effective nuclear charge, but it is higher than that for phosphorus since nitrogen is smaller.
Electronegativity generally increases across a period and decreases down a group. Oxygen is to the right of nitrogen in the same period, so oxygen has a higher effective nuclear charge and thus higher electronegativity than nitrogen. Phosphorus is below nitrogen in the same group, meaning nitrogen is smaller and its valence electrons are closer to the nucleus, resulting in higher electronegativity than phosphorus. Therefore, nitrogen's electronegativity is less than oxygen's but higher than phosphorus's.
Question 3: What, if any, effects may an increase in sodium hydroxide concentration have on the graph if done before repeating the titration?
- The pH values at the equivalence points would increase.
- The slope of the equivalence points would decrease.
- The graph would not change at all.
- The equivalence points would be reached with less volume of NaOH added. (Correct answer)
Correct answer: The equivalence points would be reached with less volume of NaOH added.
In a titration, the equivalence point is reached when the moles of titrant (NaOH) precisely react with the moles of analyte. If the concentration of the sodium hydroxide titrant is increased, a smaller volume of the solution will be needed to deliver the same number of moles required to reach the equivalence point. Consequently, the equivalence points on the titration curve would be reached with less volume of NaOH added.
Question 4: What happens to the equilibrium constant when ฮT increases, and why?
- The equilibrium constant decreases because the equilibrium shifts to the left. (Correct answer)
- The equilibrium constant increases because more products are created.
- The value for the equilibrium constant is unaffected by temperature and will not change.
- The equilibrium constant increases because the rate of the forward reaction increases.
Correct answer: The equilibrium constant decreases because the equilibrium shifts to the left.
For an exothermic reaction (ฮH < 0), an increase in temperature is analogous to adding heat to the system. According to Le Chatelier's principle, the equilibrium will shift to the left, favoring the reactants, to consume the added heat. This shift results in a lower concentration of products and a higher concentration of reactants at equilibrium, thereby causing the equilibrium constant (K) to decrease.
Question 5: A neutral atom of chlorine has a first ionization energy of 1.25 MJ/mol, while a neutral atom of argon has a first ionization energy of 1.52 MJ/mol. How would those numbers compare to the first ionization energy of a neutral potassium atom?
- Since a potassium atom is smaller than an atom of either chlorine or argon, it would be more than both.
- Because potassium has a higher nuclear charge than either chlorine or argon, it would be greater than both.
- Since potassium's valence electron is further from the nucleus than those of either chlorine or argon, it would be less than both. (Correct answer)
- With more electrons in potassium, they oppose one another more potently and require less energy to remove one, thus it would be less than both.
Correct answer: Since potassium's valence electron is further from the nucleus than those of either chlorine or argon, it would be less than both.
Ionization energy generally decreases down a group and increases across a period. Potassium (K) is in the next period below chlorine (Cl) and argon (Ar). Its valence electron is in the 4s orbital, which is significantly further from the nucleus and more shielded than the valence electrons of Cl (3p) or Ar (3p). This increased distance and shielding make it much easier to remove potassium's outermost electron, resulting in a significantly lower first ionization energy compared to both chlorine and argon.
Question 6: The gases in the container would vary from ideal conditions the greatest under which of the following circumstances, and why?
- Low temperatures, because the intermolecular forces between the gas molecules would increase (Correct answer)
- Low pressures because the gas molecules would be spread far apart
- High temperatures, because the gas molecules are moving too fast to interact with each other
- High pressures because the gas molecules will be colliding frequently
Correct answer: Low temperatures, because the intermolecular forces between the gas molecules would increase
Real gases deviate most from ideal behavior under conditions where the assumptions of the ideal gas law (no volume for particles, no intermolecular forces) break down. At low temperatures, gas molecules move slower, allowing intermolecular forces to become more significant and cause particles to attract each other. This increased interaction leads to greater deviation from ideal behavior, as the gas volume is effectively reduced and pressure is lower than predicted.
Question 7: Which of the following is supported by a review of mass spectrometry data?
- Ionization energy trends within the periodic table
- The existence of isotopes (Correct answer)
- The common oxidation states of elements
- Atomic size trends within the periodic table
Correct answer: The existence of isotopes
Mass spectrometry is a technique that measures the mass-to-charge ratio of ions. When an element is analyzed, the presence of multiple peaks at different masses but with the same charge indicates the existence of isotopes. These isotopes are atoms of the same element that have different numbers of neutrons, and thus different atomic masses, providing direct evidence for their existence and relative abundance.
Free AP Chemistry Exam Question and Answers
To produce 127 g of copper, how many moles of electrons must be transferred?