Problem 18 - Chemistry and Chemical Reactivity

Question

Give the name or formula for each ion or compound, as appropriate. (a) dichlorotetraaquachromium(III) chloride (b) \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{SO}_{4}\right] \mathrm{Cl}\) (c) sodium tetrachlorocobaltate( (11) (d) \(\left[\mathrm{Fe}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]^{3-}\)

Step-by-Step Solution

Answer

(a) Formula: \([\text{Cr}(\text{H}_2\text{O})_4\text{Cl}_2]\text{Cl}\), (b) \([\text{Cr}(\text{NH}_3)_5\text{SO}_4]\text{Cl}\), (c) Formula: \(\text{Na}_2[\text{CoCl}_4]\), (d) Complex: \([\text{Fe}(\text{C}_2\text{O}_4)_3]^{3-}\)

Step 1: Name the Ion or Compound in (a)

The compound (a) is named as dichlorotetraaquachromium(III) chloride. It contains a complex ion with chromium, two chloride ions, and four water molecules coordinated to the chromium ion. The overall formula for this compound is \([\text{Cr}(\text{H}_2\text{O})_4\text{Cl}_2]\text{Cl}\), where \(\text{Cr}^{3+}\) is the central metal ion.

Step 2: Formula Interpretation for (b)

For compound (b) \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{SO}_{4}\right]\mathrm{Cl}\), this is a complex ion with \(\text{Cr}^{3+}\) as the central ion. It coordinates with five ammonia and one sulfate (\(\mathrm{SO}_{4}^{2-}\)). The chloride ion, \(\mathrm{Cl}^{-}\), is outside the bracket indicating it as the counter ion.

Step 3: Name the Ion or Compound in (c)

The name sodium tetrachlorocobaltate(II) refers to a compound where cobalt is in the +2 oxidation state and coordinates with four chloride ions, forming \([\text{CoCl}_4]^{2-}\). Sodium ions balance the negative charge of the complex ion. The formula for this compound is \( \text{Na}_2[\text{CoCl}_4] \).

Step 4: Formula Interpretation for (d)

The compound (d) \( \left[\mathrm{Fe}\left(\mathrm{C}_{2}\mathrm{O}_{4}\right)_{3}\right]^{3-} \) consists of an iron(III) ion at the center coordinated by three oxalate ions \((\mathrm{C}_{2}\mathrm{O}_{4}^{2-})\). The overall charge of the complex is 3-.

Key Concepts

Coordination Compounds

Coordination compounds are a fascinating group of substances that consist of a central metal atom or ion bonded to a surrounding array of molecules or ions, known as ligands. Coordination compounds are characterized by their unique structures and bonding properties. This type of compound is significant in both industrial applications and biological systems.

• They are used in a variety of industrial processes, such as catalysis.
• In biology, they are essential for the function of enzymes and other biomolecules.

These compounds are also revered for their vibrant colors and are frequently used in dyes and pigments. Overall, the diversity and functionality of coordination compounds make them essential in many areas of chemistry.

Complex Ions

Complex ions are formed when ligands coordinate with a metal atom or ion, resulting in a charged entity. Understanding complex ions is crucial within the study of inorganic chemistry.

• In compound (a), the complex ion is \([\text{Cr}(\text{H}_2\text{O})_4\text{Cl}_2]^{+}\), where water and chloride function as ligands bonding with chromium.
• The formula \([\mathrm{Cr}\left(\mathrm{NH}_3\right)_5\mathrm{SO}_4]^{+}\) in compound (b) forms a complex ion with ammonia and sulfate as coordinating species.

Complex ions determine the compounds' overall charge and affect their catalytic and reactive properties. They are essential in fields ranging from synthetic chemistry to the design of new materials.

Oxidation States

The concept of oxidation states helps us comprehend the electron distribution in chemical compounds. It refers to the hypothetical charge an atom would have if all bonds were ionic, and it's fundamental in writing and understanding formulas for coordination compounds.

In many coordination compounds, the oxidation state of the metal is crucial for determining the chemical behavior of the compound.

• In compound (a), the chromium has an oxidation state of +3, explaining its coordination with six ligands.
• For compound (c), cobalt is in the +2 oxidation state, influencing the properties and reactivity of \([\text{CoCl}_4]^{2-}\).

The oxidation state is pivotal in predicting the geometry and bonding characteristics, which influence the substance's chemical reaction patterns.

Ligands

Ligands are atoms, ions, or molecules that donate electron pairs to a central atom or ion in a coordination complex. They are essential in determining the structure and stability of the compound.

• Ligands like water and ammonia play a crucial role in compounds (a) and (b) to form coordinate bonds with chromium.
• Chloride ions in compound (c) and oxalate ions in compound (d) also serve as ligands, stabilizing complex ions.

Ligands can vary in charge, size, and the number of donor atoms they contain, which allows for a great diversity in the coordination compounds they form. Their presence and nature affect the physical properties like color, magnetism, and solubility of coordination compounds.