Problem 70 - General Chemistry: Principles and Modern Applications

Question

The oxidation state of \(\mathrm{Ni}\) in the complex ion \(\left[\mathrm{Ni}(\mathrm{CN})_{4} \mathrm{I}\right]^{3-}\) is \((\mathrm{a})-3 ;(\mathrm{b})-2 ;(\mathrm{c}) 0 ;(\mathrm{d})+2 ;(\mathrm{e})+3\).

Step-by-Step Solution

Answer

The oxidation state of Ni in the complex ion \(\left[\mathrm{Ni}(\mathrm{CN})_{4} \mathrm{I}\right]^{3-}\) is +2 (option d).

Step 1: Determine the oxidation states of known atoms

The oxidation state of Cyanide Ion (CN) is always -1 and for Iodine Ion (I) is -1.

Step 2: Formulate the oxidation state equation

Let x be the oxidation state of Ni, write the equation as: \(x + 4(-1) + (-1)\) = -3, as the overall charge of the complex ion is -3.

Step 3: Solve for x

Solving the equation, the oxidation state of Ni (x) = -3 + 4 + 1 = 2.

Key Concepts

Complex Ions

Complex ions are a staple of coordination chemistry, which consists of a central metal atom or ion that's surrounded by a group of molecules or anions, known as ligands. The ligands have at least one lone electron pair they can donate to the metal, forming coordinate covalent bonds. A key property of these ions is their ability to adopt multiple oxidation states.

For example, the complex ion \(\left[\mathrm{Ni}(\mathrm{CN})_{4} \mathrm{I}\right]^{3-}\) contains nickel as the central ion with cyanide and iodide ligands. Oxidation states must be determined to understand the metal's electron configuration and predict its reactivity and magnetic properties. This ion's overall charge is derived from the combination of the oxidation state of nickel and the known charges of the ligands.

Coordination Chemistry

Coordination chemistry focuses on the study of complex ions and the coordination compounds formed by them. It plays a critical role in the development of materials and catalysts, and is essential in biochemical systems as well. Central metal atoms or ions, like nickel, cobalt, or iron, can coordinate with many types of ligands to form diverse structures with unique properties.

Oxidation states in coordination compounds are especially important because they can influence color, magnetism, and reactivity. For instance, different oxidation states of the same metal in a coordination compound can result in different colors, a concept useful in identifying or designing compounds for specific purposes.

Redox Reactions

Redox reactions are chemical reactions that involve the transfer of electrons between species. These reactions are characterized by the change in oxidation states of atoms or ions during the process. One species will have electrons removed (oxidation), while another gains electrons (reduction).

Understanding the oxidation state is essential to balance redox reactions. For example, in the complex ion \(\left[\mathrm{Ni}(\mathrm{CN})_{4} \mathrm{I}\right]^{3-}\), the oxidation state of nickel determines how it will behave in redox processes. If nickel were to undergo a reduction, it would gain electrons and its oxidation state would decrease. Conversely, if oxidized, it would lose electrons and its oxidation state would increase. The accurate determination of these states is therefore crucial for predicting the redox behavior of complex ions.