FREE AP Chemistry Exam Question and Answers

Question 1

To produce 127 g of copper, how many moles of electrons must be transferred?

Accepted Answer

two mole of electrons

Answer

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 Cu⁺ ion (cuprous ion), then each mole of copper requires 1 mole of electrons (Cu⁺ + e⁻ → 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?

Accepted 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.

Answer

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?

Accepted Answer

The equivalence points would be reached with less volume of NaOH added.

Answer

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 ΔT increases, and why?

Accepted Answer

The equilibrium constant decreases because the equilibrium shifts to the left.

Answer

For an exothermic reaction (ΔH < 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?

Accepted Answer

Since potassium's valence electron is further from the nucleus than those of either chlorine or argon, it would be less than both.

Answer

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.

AP Practice Test

AP Practice Test

FREE AP Chemistry Exam Question and Answers