Problem 32 - Chemistry and Chemical Reactivity

Question

Give the name or formula for each ion or compound, as appropriate. (a) tetraaquadichlorochromium(III) chloride (b) \(\left|\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{SO}_{4}\right| \mathrm{Cl}\) (c) sodium tetrachlorocobaltate(II) (d) \(\left[\mathrm{Fe}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]^{3}\)

Step-by-Step Solution

Answer

(a) \[ [\text{Cr}(\text{H}_2\text{O})_4\text{Cl}_2]\text{Cl} \]; (b) pentaammine(sulfato)chromium(III) chloride; (c) \[ \text{Na}_2[\text{CoCl}_4] \]; (d) tris(oxalato)ferrate(III) ion.

Step 1: Understand the Question

The task is to identify the correct names or formulas for various ions or compounds. Each part requires interpreting chemical nomenclature or formulas to determine the corresponding chemical compound or name.

Step 2: Naming Coordination Compounds (a)

For (a) tetraaquadichlorochromium(III) chloride, we identify the components: 'tetraaqua' means four water molecules (H₂O), 'dichloro' means two chloride ions (Cl⁻), and 'chromium(III)' indicates a chromium ion with a +3 charge. The overall compound is \[ [\text{Cr}(\text{H}_2\text{O})_4\text{Cl}_2]\text{Cl} \]

Step 3: Writing Formula for Complex Ion (b)

For (b), the complex \[ \left|\mathrm{Cr}\left(\mathrm{NH}_3\right)_{5}\mathrm{SO}_4\right|\mathrm{Cl}\] is described as pentaammine(sulfato)chromium(III) chloride, where the chromium is coordinated to five ammonia (NH₃) molecules and one sulfate (SO₄²⁻) group. This complex ion is paired with a chloride ion (Cl⁻).

Step 4: Naming for Coordination Complex Compound (c)

For (c) sodium tetrachlorocobaltate(II), it contains sodium ions and a complex ion. 'Tetrachloro' indicates four chloride ions attached to cobalt. Since cobalt (II) suggests a +2 oxidation state, the complex ion is \[ \text{Na}_2[\text{CoCl}_4] \].

Step 5: Writing Formula for Complex Ion (d)

For (d), the notation \[ \left[\mathrm{Fe}\left(\mathrm{C}_{2}\mathrm{O}_{4}\right)_{3}\right]^{3-} \] describes a complex ion, iron coordinated to three oxalate (C₂O₄²⁻) ligands, giving it an overall -3 charge. Hence, the complex is known as tris(oxalato)ferrate(III).

Key Concepts

Chemical Nomenclature

Chemical nomenclature is the system of naming chemical compounds. It's essential for scientists and students to communicate about different substances. In coordination chemistry, these names often describe the composition of complex ions. Two key aspects are the ligands surrounding a central metal atom and the oxidation state of the metal.
For example, when naming the compound tetraaquadichlorochromium(III) chloride, each part provides information about the molecule. 'Tetra-aqua' indicates four water molecules are ligands. 'Dichloro' shows the presence of two chloride ions. Lastly, 'chromium(III)' tells us about the oxidation state, which is +3 for the chromium ion.
Understanding these components helps in deducing the formula for the compound. Here, it leads to \[ [\text{Cr}(\text{H}_2\text{O})_4 \text{Cl}_2] \text{Cl} \]. Students should practice identifying such key terms to become proficient in chemical nomenclature.

Complex Ion Structures

Complex ion structures involve central metal ions surrounded by ligands. These can vary significantly in geometry and charge depending on the number and type of ligands.
In the example \[ \left[ \mathrm{Cr} \left( \mathrm{NH}_3 \right)_5 \mathrm{SO}_4 \right] \mathrm{Cl} \], the central chromium ion is coordinated with five ammonia molecules and one sulfate group. Ammonia, a neutral ligand, doesn't alter the oxidation state of chromium. However, sulfate, with a -2 charge, adds complexity.
Recognizing these structures is crucial for understanding the properties and reactivity of the compounds. The spatial arrangement of ligands impacts the physical and chemical behavior of the molecule. Students can benefit from visualizing these arrangements to gain a deeper comprehension of complex ion formation.

Oxidation States

Oxidation states indicate the degree of oxidation of an atom in a compound. It's vital in naming and structuring chemical species. The oxidation state helps determine the electronic configuration and reactivity of the compound.
Consider sodium tetrachlorocobaltate(II). Here, cobalt's oxidation state is +2, confirming its name's part "cobaltate(II)." Knowing this allows one to deduce the formula\[ \text{Na}_2 [\text{CoCl}_4] \]. Each chloride ion has a -1 charge, meaning the combination balances the +2 state of cobalt to achieve electrical neutrality.
Oxidation states are crucial for further studies in redox reactions and electrochemical cells. Calculating them correctly enables a clear understanding of the synthetic and reaction processes of coordination compounds, essential in both academic and industrial chemistry.

Ligands in Coordination Compounds

Ligands are ions or molecules that donate electrons to a metal atom in a coordination compound. They play a key role in the stability and reactivity of the complex. Depending on their charge and type, they influence the compound's properties significantly.
In the formula \[ \left[ \mathrm{Fe} \left( \mathrm{C}_2 \mathrm{O}_4 \right)_3 \right]^{3-} \], oxalate acts as a bidentate ligand, meaning it can form two bonds with the central metal ion. This gives additional stability to the complex.
Ligands can be classified based on their denticity and charge. Knowing these attributes helps predict the resulting compound's behavior in different chemical environments. Familiarity with typical ligands like water, ammonia, chloride, and oxalate is helpful for students learning about coordination chemistry. This knowledge is foundational for understanding complex synthesis and reactions in advanced studies.