Question

When iron(II) oxalate (oxalate \(=\mathrm{ox}^{2-}\) ) is treated with \(\mathrm{H}_{2} \mathrm{O}_{2}, \mathrm{H}_{2} \mathrm{ox}\) and \(\mathrm{K}_{2}\) ox, a green compound \(\mathrm{X}\) is obtained. \(\mathbf{X}\) reacts with aqueous \(\mathrm{NaOH}\) to give hydrated \(\mathrm{Fe}_{2} \mathrm{O}_{3},\) and is decomposed by light with production of iron(II) oxalate, \(\mathrm{K}_{2}\) ox and \(\mathrm{CO}_{2}\). Analysis of \(\mathrm{X}\) shows it contains \(11.4 \%\) Fe and \(53.7 \%\) ox \(^{2-}\). Deduce the formula of \(\mathbf{x}\) and write equations for its reaction with alkali and its photochemical decomposition. State, with reasons, whether you would expect \(\mathbf{X}\) to be chiral

Short answer

The formula of X is \[ \text{K}_3[\text{Fe(C}_2\text{O}_4)_3]\cdot\text{3H}_2\text{O} \]. Reaction with NaOH yields \(\text{Fe}_2\text{O}_3\), and light decomposition yields \(\text{Fe(C}_2\text{O}_4)",, \text{K}_2\text{C}_2\text{O}_4\), \(\text{CO}_2 \). X is chiral.

Step-by-step solution

Determine the molecular formula of X

Given that compound X contains 11.4% Fe and 53.7% oxalate (ox\(^{2-}\)), we can determine its molecular composition. Assume 100 g of compound \(X\). This gives 11.4 g of Fe and 53.7 g of oxalate. The molar mass of Fe is \(55.85\, \text{g/mol}\), giving \(\frac{11.4}{55.85} \approx 0.204\, \text{mol}\) of Fe. The molar mass of \(\text{C}_2\text{O}_4^{2-}\) is \(88.0\, \text{g/mol}\), giving \(\frac{53.7}{88.0} \approx 0.610\, \text{mol}\) of oxalate. This suggests a molar ratio of Fe to oxalate of approximately \(1:3\), implying \(\text{Fe(C}_2\text{O}_4)_3^{3-}\) is a plausible core structure.

Complement molecular formula of X with K and H

In the formation of \(X\), \(\text{K}_2\text{Ox}\) and \(\text{H}_2\text{Ox}\) are involved. With the calculated composition from the previous step, balancing the charge and integrating the K and H from reactants suggest the molecular formula: \(\text{K}_3\text{[Fe(C}_2\text{O}_4)_3]\cdot\text{3H}_2\text{O}\), a potassium iron(III) oxalate complex with water of hydration.

Reaction of X with NaOH

\(X\), \(\text{K}_3[\text{Fe(C}_2\text{O}_4)_3]\cdot\text{3H}_2\text{O}\), reacts with NaOH to yield hydrated ferric oxide (\(\text{Fe}_2\text{O}_3\cdot\text{xH}_2\text{O}\)) and other species. The reaction is as follows:\[ \text{K}_3[\text{Fe(C}_2\text{O}_4)_3]\cdot\text{3H}_2\text{O} + 6\text{NaOH} \rightarrow \text{Fe}_2\text{O}_3\cdot\text{3H}_2\text{O} + 3\text{KOH} + \text{Na}_2\text{C}_2\text{O}_4 + 3\text{H}_2\text{O}\]

Photochemical decomposition of X

When decomposed by light, \(X\), potassium iron(III) oxalate decomposes back into iron(II) oxalate, \(\text{K}_2\text{C}_2\text{O}_4\) and \(\text{CO}_2\). The reaction is:\[ \text{K}_3[\text{Fe(C}_2\text{O}_4)_3]\rightarrow \text{Fe(C}_2\text{O}_4) + \text{K}_2\text{C}_2\text{O}_4 + \text{CO}_2\]

Determine chirality of X

The complex \(\text{K}_3[\text{Fe(C}_2\text{O}_4)_3]\) could potentially be chiral due to the presence of asymmetry in the arrangement of oxalate ligands around the iron center, forming optical isomers. Thus, \(X\) is expected to be chiral.

Key concepts

Iron(II) Oxalate

Iron(II) oxalate is an inorganic compound composed of iron and oxalate ions. The chemical formula for iron(II) oxalate is \( ext{{FeC}}_2 ext{{O}}_4\), where the iron is in the +2 oxidation state. This compound often appears as a pale yellow or light green powder, which is relatively insoluble in water.

• Composition: Iron in iron(II) oxalate contributes to the metal's reactivity and coordination chemistry. Meanwhile, the oxalate anion \(\text{{C}}_2\text{{O}}_4^{2-}\) acts as a bidentate ligand, meaning it can form two bonds with a metal center.

Iron(II) oxalate is typically used in the preparation of other iron complexes and can engage in various reactions, often requiring oxidative conditions to transform into different species.
In the context of the exercise, iron(II) oxalate undergoes decomposition through photochemical processes and other reactions, illustrating its versatile role in inorganic chemistry.

Potassium Iron(III) Oxalate

Potassium iron(III) oxalate is a complex coordination compound containing potassium ions, iron in the +3 oxidation state, and oxalate ions. This compound is represented by the formula \( ext{{K}}_3[ ext{{Fe(C}}_2 ext{{O}}_4)_3]\cdot ext{{3H}}_2 ext{{O}}\), which indicates the presence of three potassium ions per formula unit and three water molecules of hydration.

• Complex Structure: The iron(III) center is surrounded by three oxalate ligands, each forming bidentate chelation, resulting in a stable complex geometry.

Potassium iron(III) oxalate exhibits interesting properties due to its complex structure, including its green color, which is typical for iron(III) compounds. In the exercise, its formation from iron(II) oxalate involves oxidation and the incorporation of potassium ions to stabilize the trivalent iron state.
This compound serves as a precursor to various reactions, including photochemical decomposition, showcasing its reactive capabilities in sunlight, a trait that is exploited in certain analytical applications.

Photochemical Decomposition

Photochemical decomposition refers to the breaking down of compounds through the action of light, typically ultraviolet or visible light. This kind of reaction plays an essential role in the transformation of inorganic complexes.

• Decomposition Reaction: In the given exercise, potassium iron(III) oxalate decomposes under light exposure to revert back to iron(II) oxalate, along with the production of potassium oxalate and carbon dioxide. The reaction can be expressed as \[\text{{K}}_3[\text{{Fe(C}}_2\text{{O}}_4)_3] \rightarrow \text{{Fe(C}}_2\text{{O}}_4) + \text{{K}}_2\text{{C}}_2\text{{O}}_4 + \text{{CO}}_2\]

This process emphasizes the role of light in altering the chemical state of compounds, a principle also pivotal in areas like photochemistry and environmental science. The ability of a compound to undergo photochemical decomposition is often explored for its potential applications in light-driven processes.

Chirality in Inorganic Complexes

Chirality is a property wherein a compound exhibits non-superimposable mirror images, like the left and right hands. Although chirality is more commonly associated with organic chemistry, it also plays a fascinating role in inorganic complexes.

• Coordination Chemistry: In the exercise, the compound \(\text{{K}}_3[\text{{Fe(C}}_2\text{{O}}_4)_3]\) potentially exhibits chirality due to the spatial arrangement of its ligands. The oxalate ligands can create an asymmetric environment around the iron center, allowing for the existence of optically active isomers.

This attribute is essential in the study of stereochemistry, where the optical activity of a compound can significantly influence its behavior and interaction with other molecules.
Understanding chirality in inorganic complexes aids in grasping how these structures can impact areas ranging from catalysis to materials science, and opens up venues for research into enantiomer selectivity and function.