Problem 177 - A Complete Resource Book in Chemistry for JEE Main

Question

Which series of reactions correctly represents chemical relations related to iron and its compound? \([2014]\) (a) \(\mathrm{Fe} \stackrel{\mathrm{C}_{2} \text { heat }}{\longrightarrow} \mathrm{FeCl}_{3} \stackrel{\text { het air }}{\longrightarrow}\) \(\mathrm{FeCl}_{2} \stackrel{\mathrm{Zn}}{\longrightarrow} \mathrm{Fe}\) (b) \(\mathrm{Fe} \stackrel{\mathrm{O}_{3} \mathrm{haat}}{\longrightarrow} \mathrm{FeCl}_{3} \stackrel{\mathrm{CO}, 600^{\circ} \mathrm{C}}{\longrightarrow} \mathrm{FeO}\) \(\stackrel{\cos w^{2} \mathrm{C}}{\longrightarrow} \mathrm{Fe}\)c) \(\mathrm{Fe} \stackrel{\mathrm{d} \mathrm{H}_{\mathrm{H}} \mathrm{SO}_{4}}{\longrightarrow} \mathrm{FeSO}_{4} \stackrel{\mathrm{H}, \mathrm{So}_{4}, \mathrm{O}_{3}}{\longrightarrow}\) \(\mathrm{Fe}_{2}\left(\mathrm{SO}_{4}\right)_{2} \stackrel{\text { Heat }}{\longrightarrow} \mathrm{Fe}\) d) \(\mathrm{Fe} \stackrel{\mathrm{O}_{\mathrm{b} \mathrm{ben}}}{\longrightarrow} \mathrm{FeSO}_{4} \stackrel{\mathrm{diH}_{2} \mathrm{So}_{4}}{\longrightarrow}\) \(\mathrm{FeSO}_{4} \stackrel{\text { Heart }}{\longrightarrow} \mathrm{Fe}\)

Step-by-Step Solution

Answer

None of these reaction sequences correctly represent feasible iron chemistry.

Step 1: Analyze Reaction Series (a)

For reaction series (a), we have the following sequence: Fe with heat forms \( \mathrm{FeCl}_3 \) and then \( \mathrm{FeCl}_3 \) in air forms \( \mathrm{FeCl}_2 \). Finally, \( \mathrm{FeCl}_2 \) with Zn forms Fe. This sequence involves a reduction of iron in the chloride form, but the initial reaction is incorrect since iron chlorides are not produced by direct heating with carbon.

Step 2: Analyze Reaction Series (b)

In reaction series (b), Fe is converted into \( \mathrm{FeCl}_3 \) by heating (although the reagents are inaccurately represented), then \( \mathrm{FeCl}_3 \) is converted into \( \mathrm{FeO} \) using CO at 600°C, and finally \( \mathrm{FeO} \) is reduced to Fe by further heating. However, this sequence is not chemically feasible as it involves incorrect reactions.

Step 3: Analyze Reaction Series (c)

For reaction series (c), Fe is transformed into \( \mathrm{FeSO}_4 \) using diluted \( \mathrm{H}_2\mathrm{SO}_4 \), then into \( \mathrm{Fe}_2(\mathrm{SO}_4)_3 \) using \( \mathrm{H}_2\mathrm{SO}_4 \) and \( \mathrm{O}_3 \), and finally, heating \( \mathrm{Fe}_2(\mathrm{SO}_4)_3 \) forms Fe. However, this notification is inconsistent as heating \( \mathrm{Fe}_2(\mathrm{SO}_4)_3 \) doesn't yield Fe directly.

Step 4: Analyze Reaction Series (d)

For reaction series (d), Fe is reacted to form \( \mathrm{FeSO}_4 \), followed by heating with diluted \( \mathrm{H}_2\mathrm{SO}_4 \). However, the final step mistakenly states that \( \mathrm{FeSO}_4 \) becomes Fe upon heating, which is incorrect as it would decompose to ferric oxide and SO2.

Step 5: Determine the Correct Series

Assessing all series, none provide a completely correct sequence of reactions according to standard chemical knowledge about iron and its transformations. Generally, Fe is oxidized to ferric or ferrous compounds rather than reduced directly back to elemental Fe as described.

Key Concepts

Redox Reactions

Understanding redox reactions is crucial in chemistry, especially when discussing iron transformations. Redox, short for reduction-oxidation, involves the transfer of electrons between substances, causing one to gain electrons (reduction) and the other to lose electrons (oxidation). In reactions concerning iron, we usually observe iron either gaining oxygen (oxidation) or losing oxygen or gaining electrons (reduction).

For instance, when iron reacts with oxygen in the air, it forms iron oxides, like rust, which is a form of oxidation. Conversely, when a reducing agent, like carbon monoxide, is used, it can reduce iron oxide back to pure iron by removing the oxygen, showcasing reduction. In the context of the discussed reactions, such as iron being converted to iron chlorides or iron sulfates and back to elemental iron, recognizing the redox processes is key.

Iron (Fe) typically transitions between ferrous ( Fe^{2+}) and ferric (Fe^{3+}) states in redox reactions. This dynamic balance makes studying redox reactions involving iron fascinating as it involves a complex interplay between different states and compounds.

Iron Compounds

Iron forms a variety of compounds that are crucial in different chemical processes and industrial applications. Two main iron oxides are ferrous oxide (FeO) and ferric oxide (Fe_2O_3). Each plays different roles, such as pigmentation or as precursors in producing pure iron through redox reactions.

Another common class of iron compounds includes iron sulfates. Ferrous sulfate ( FeSO_4) and ferric sulfate ( Fe_2(SO_4)_3) are often used in water treatment and as mordants in textile dyeing. They illustrate iron's ability to form stable compounds with other elements.

Iron chlorides, such as ferrous chloride (FeCl_2) and ferric chloride (FeCl_3), are essential in different industrial processes, including sewage treatment and as catalysts. These chlorides demonstrate iron's reactivity and versatility as they can engage in various chemical transformations, either serving as products of reaction or intermediates.

Chemical Transformations

Chemical transformations involving iron are varied and depend heavily on the reaction conditions and reagents. These transformations might involve changes in the oxidation state of iron or its combination with other elements to form new compounds.

Under the right conditions, as shown in the exercise, iron can switch from elemental state to compounds such as iron sulfates or iron oxides. However, these processes require precise conditions, often involving heat or specific chemical environments. It's also crucial to note that not all proposed reactions are feasible in real-life laboratory settings due to the requirement of actual energetic feasibilities and correct reactants.

For example, smelting iron ore into pure iron involves high-temperature reduction processes primarily using carbon-based agents. In contrast, creating iron sulfate from elemental iron requires the precise application of sulfuric acid. Each of these transformations showcases not only the versatility of iron but also the intricate control needed over chemical conditions.