MCAT General Chemistry Practice Questions with Correct Answers. (A+ Paper)

Which of the following statements accurately describes the difference between a sigma (σ) and a pi (π) bond? A. Pi bonds form from the side-to-side overlap of hybridized sp, sp^2, sp^3 superscript orbitals. B. Sigma bonds form from the end-to-end overlap of two hybridized s or p orbitals. C. The maximum number of σ versus π bonds between two atoms are different, but the energy level of the two bonds are the same. D. Only sigma bonds use hybridized orbitals to overlap in forming the bond. Correct Answer Only sigma bonds use hybridized orbitals to overlap in forming the bond. In regards to the total possible number of bonds between two atoms, the total possible number of bonds for a σ bond is one and for a π bond is two. In regards to the energy level, a sigma bond is lower in energy than a π bond. A sigma σ bond will form from an end-to-end overlap of an s, p, or hybridized orbital. A π bond will only form from the side-to-side overlap of two unhybridized p orbitals. Since π bonds only use unhybridized orbitals, only sigma bonds use hybridized orbitals to overlap in forming the bond. It is the correct answer. Suppose a weak acid has a Ka = 4.0 x 10^-9. Which of the following gives its equivalent Kb? 4.0 x 10^-8 1.5 x 10^-10 2.5 x 10^-6 3.0 x 10^-11 Correct Answer 2.5 x 10^-6 Kw = 10^-14 Ka x Kb = Kw (10^-14) / (4.0 x 10^-9) = 2.5 x 10^-6 Which of the following best describes a chemical species that is measured to have Kb = 3.2 x 10^-18? A strong base