IMAT - International Medical Admissions Chemical Bonding and Reactions Questions and Answers — Questions and Answers
Question 1: Which of the following compounds contains both ionic and covalent bonds?
- NaCl
- CH₄
- NH₄Cl (Correct answer)
- H₂O
Correct answer: NH₄Cl
Ammonium chloride (NH₄Cl) is composed of the ammonium cation (NH₄⁺) and the chloride anion (Cl⁻). The electrostatic attraction between these two ions forms an ionic bond. Within the ammonium cation, the nitrogen atom is bonded to four hydrogen atoms through polar covalent bonds.
Question 2: Based on the principles of intermolecular forces, which of the following substances is expected to have the highest boiling point?
- NH₃ (Ammonia)
- H₂O (Water) (Correct answer)
- CH₄ (Methane)
- HF (Hydrogen Fluoride)
Correct answer: H₂O (Water)
Water (H₂O) has the highest boiling point among the choices. While H₂O, NH₃, and HF all exhibit strong hydrogen bonding, water is unique in its ability to form an extensive three-dimensional network of hydrogen bonds. Each water molecule can act as a hydrogen bond donor twice and an acceptor twice, leading to a maximum of four hydrogen bonds per molecule. This creates a very strong cohesive force that requires more energy to overcome compared to the hydrogen bonding in HF or NH₃.
Question 3: In the single displacement reaction: Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s), which species acts as the oxidizing agent?
- Zn(s)
- Cu(s)
- Zn²⁺(aq)
- CuSO₄(aq) (Correct answer)
Correct answer: CuSO₄(aq)
The oxidizing agent is the substance that causes oxidation by accepting electrons, and in the process, it gets reduced. In this reaction, the copper ion (Cu²⁺) in copper sulfate gains two electrons to become solid copper (Cu). Since the copper ion's oxidation state decreases from +2 to 0, it is reduced, making CuSO₄ the oxidizing agent.
Question 4: Consider the reversible reaction for the Haber process: N₂(g) + 3H₂(g) ⇌ 2NH₃(g), which is an exothermic reaction. According to Le Chatelier's principle, which of the following changes will shift the equilibrium to the right, favoring the production of ammonia?
- Increasing the temperature
- Adding a catalyst
- Decreasing the pressure
- Increasing the pressure (Correct answer)
Correct answer: Increasing the pressure
According to Le Chatelier's principle, if a change of condition is applied to a system in equilibrium, the system will shift in a direction that relieves the stress. The reactant side has 4 moles of gas (1+3), while the product side has 2 moles of gas. Increasing the pressure creates a stress that the system relieves by shifting to the side with fewer moles of gas. Therefore, increasing the pressure will shift the equilibrium to the right, favoring the formation of NH₃.
Question 5: According to the Brønsted-Lowry theory of acids and bases, a base is defined as a substance that:
- donates a proton (H⁺)
- accepts a proton (H⁺) (Correct answer)
- produces hydroxide ions (OH⁻) in water
- accepts an electron pair
Correct answer: accepts a proton (H⁺)
The Brønsted-Lowry theory defines acids and bases in terms of proton transfer. A Brønsted-Lowry acid is a proton (H⁺) donor, while a Brønsted-Lowry base is any species that can accept a proton.
Question 6: A student is observing the reaction between a solid piece of marble (calcium carbonate, CaCO₃) and hydrochloric acid (HCl). Which of the following actions would most likely DECREASE the rate of the reaction?
- Using a more concentrated solution of HCl
- Grinding the marble into a fine powder
- Cooling the reaction mixture in an ice bath (Correct answer)
- Gently stirring the mixture
Correct answer: Cooling the reaction mixture in an ice bath
Reaction rates are generally decreased by lowering the temperature. Cooling the mixture reduces the kinetic energy of the reactant particles, leading to fewer collisions per unit of time and a smaller proportion of collisions having sufficient energy to overcome the activation energy barrier. Increasing concentration, increasing surface area (grinding), and stirring all typically increase the reaction rate.
IMAT - International Medical Admissions Chemical Bonding and Reactions Questions and Answers
Which of the following compounds contains both ionic and covalent bonds?