Ni2+(aq) + 6 NH3(aq) → [Ni(NH3)6]2+(aq) The reaction represented above is best classified as — Acids and Bases Chemistry Question

STEPS:

1. Identify the reactants and product of the reaction: The chemical equation given in the question is $\text{Ni}^{2+}(aq) + 6\text{ NH}_3(aq) \rightarrow [\text{Ni}(\text{NH}_3)_6]^{2+}(aq)$.
2. Examine the bonding behavior: This equation represents the formation of a metal-ligand coordination complex, where a central metal cation is surrounded by coordinate covalent ligands.
3. Apply the Lewis definition of acids and bases: A Lewis base is defined as an electron-pair donor, and a Lewis acid is defined as an electron-pair acceptor.
4. Determine the roles of the reactants: Ammonia ($\text{NH}_3$) possesses a lone pair of electrons on its nitrogen atom, which it donates to the empty d-orbitals of the transition metal cation, nickel(II) ($\text{Ni}^{2+}$), to form coordinate covalent bonds.
5. Classify the reaction: Because $\text{Ni}^{2+}$ acts as the electron-pair acceptor (the Lewis acid) and $\text{NH}_3$ acts as the electron-pair donor (the Lewis base), the process is best classified as a Lewis acid-base reaction.

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WHY_OTHERS_WRONG:

• B is incorrect: A Brønsted^-Lowry acid-base reaction is defined by the transfer of protons ($\text{H}^+$) between species. No proton transfer occurs in this reaction.
• C is incorrect: An Arrhenius acid-base reaction requires the acid to increase the concentration of hydrogen ions ($\text{H}^+$) and the base to increase the concentration of hydroxide ions ($\text{OH}^-$) in aqueous solution. Neither species behaves this way in the equation.
• D is incorrect: An oxidation-reduction reaction requires a change in oxidation numbers due to the transfer of electrons. In this reaction, the oxidation state of nickel remains $+2$, and the oxidation states of nitrogen ($-3$) and hydrogen ($+1$) remain unchanged.
• E is incorrect: A precipitation reaction involves the combination of aqueous reactants to produce an insoluble solid precipitate. The product complex is explicitly labeled as aqueous ($aq$), meaning it remains fully dissolved in solution.

🧪 I can walk you through the step-by-step solutions for any other complex-ion or coordinate-bonding questions found in your AP Chemistry sources.