MCAT General Chemistry Question 39: Answer and Explanation

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Question: 39

9. Which of the following best describes the number and character of the bonds in an ammonium cation?

A. Three polar covalent bonds
B. Four polar covalent bonds, of which none are coordinate covalent bonds
C. Four polar covalent bonds, of which one is a coordinate covalent bond
D. Four polar covalent bonds, of which two are coordinate covalent bonds

Correct Answer: C

Explanation:

First recall that ammonium is NH₄⁺, while ammonia is NH₃. Ammonium is formed by the association of NH₃, an uncharged molecule with a lone pair on the nitrogen, with a positively charged hydrogen cation. In other words, NH₃ is a Lewis base, while H⁺ is a Lewis acid. This type of bonding between a Lewis acid and base is a coordinate covalent bond.

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