Problem 88 - A Complete Resource Book in Chemistry for JEE Main

Question

In the reaction: \(\mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]+\mathrm{K}_{2} \mathrm{CO}_{3} \longrightarrow\) the product formed is (a) \(\mathrm{FeCO}_{3}\) (b) \(\mathrm{KCN}\) (c) \(\mathrm{KFeCO}_{3}\) (d) \(\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{4}\right]\)

Step-by-Step Solution

Answer

The product formed is \( \mathrm{FeCO}_{3} \), which corresponds to option (a).

Step 1: Analyze the Given Reactants

We are given the chemical reaction: \( \mathrm{K}_{4}[\mathrm{Fe}(\mathrm{CN})_{6}] + \mathrm{K}_{2} \mathrm{CO}_{3} \rightarrow \). Here, \( \mathrm{K}_{4}[\mathrm{Fe}(\mathrm{CN})_{6}] \) is potassium hexacyanoferrate(II) and \( \mathrm{K}_{2} \mathrm{CO}_{3} \) is potassium carbonate.

Step 2: Understand the Possible Chemical Changes

Potassium hexacyanoferrate(II) can potentially undergo decomposition or displacement reactions, releasing cyanide ions, while potassium carbonate can provide carbonate ions. The combination hints at a possible displacement of cyanide by carbonate ions.

Step 3: Predict the Reaction Outcome

The potential displacement of cyanide ions by carbonate ions in the presence of strong alkalis like potassium carbonate suggests the formation of a ferric carbonate, \( \mathrm{FeCO}_{3} \). Other possibilities like potassium cyanide, \( \mathrm{KCN} \), are less likely due to the stable complex nature of \( \mathrm{K}_{4}[\mathrm{Fe}(\mathrm{CN})_{6}] \).

Step 4: Determine the Product

Considering the stability of \( \mathrm{FeCO}_{3} \) in this analagous exchange reaction, the compound \( \mathrm{FeCO}_{3} \) seems to be the likely precipitate. This is represented by option (a) in the answer choices.

Key Concepts

Potassium Hexacyanoferrate(II)

Potassium hexacyanoferrate(II), often written as \( \mathrm{K}_{4}[\mathrm{Fe}(\mathrm{CN})_{6}] \), is a complex salt composed of potassium, iron, and cyanide ions. This compound forms a stable complex due to the coordination between the iron ion and cyanide groups. This coordination is key to its chemical stability and influences how it reacts with other compounds.

• The complex is highly stable due to the strong bond between the iron and cyanide ions.
• This stability means that the cyanide ions are not easily displaced unless under specific reaction conditions.
• The compound's color can range from yellow to red, and it is soluble in water, allowing it to be used in various chemical reactions.

Understanding how Potassium hexacyanoferrate(II) behaves is crucial because its stability affects its likelihood to participate in displacement reactions. Any change implies significant energy interactions to break the complex structure.

Displacement Reactions

Displacement reactions occur when an element in a compound is replaced by another element. This type of reaction is common in chemistry and generally involves metals and halogens swapping places. In the context of Potassium hexacyanoferrate(II), displacement can occur but with some resistance due to the strong complex bonds.

• These reactions help predict product formation when different substances are mixed.
• The stability of the original complex affects the ease of the reaction. In our case, it requires a strong impetus to displace cyanide ions.
• Chemists often look for such opportunities where a less stable ion or molecule can be replaced by another.

In the exercise, a potential displacement reaction between cyanide and carbonate ions is considered, driven by the introduction of potassium carbonate. This predicts the formation of new compounds even when the original compounds are stable.

Ferric Carbonate Formation

Ferric carbonate, \( \mathrm{FeCO}_{3} \), can be formed through the reaction between iron ions and carbonate ions. This formation is an example of a displacement reaction, where the original ions in the compound are replaced to form a new substance.

• Ferric carbonate often precipitates out of solution, as it is not particularly soluble in water.
• When formed in reactions involving strong complexes like \( \mathrm{K}_{4}[\mathrm{Fe}(\mathrm{CN})_{6}] \), it indicates a successful displacement of complexed ions.
• The properties of the resulting precipitate can also confirm the nature of the displacement reaction.

The formation of \( \mathrm{FeCO}_{3} \) as predicted in the solution indicates a successful outcome with stable iron-carbonate compounds as products. This shows how displacement reactions can result in observable changes and new material formations.