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Chapter 19: Problem 82

When \(\mathrm{MnO}_{2}\) is fused with KOH, a coloured compound is formed. The product and its colour is (a) \(\mathrm{K}_{2} \mathrm{MnO}_{4}\), purple green (b) \(\mathrm{KMnO}_{4}\), purple (c) \(\mathrm{Mn}_{2} \mathrm{O}_{3}\), brown (d) \(\mathrm{Mn}_{3} \mathrm{O}_{4}\), black

Short Answer

Expert verified
The product is (a) \(\mathrm{K}_{2}\mathrm{MnO}_{4}\), green.

Step by step solution

01

Understand the Reaction

When manganese dioxide (\(\mathrm{MnO}_2\)) is fused with potassium hydroxide (\(\mathrm{KOH}\)), the reaction takes place under oxidizing conditions. The key is recognizing that this fusion often involves an oxidation process.
02

Determine the Products

Given the conditions, (\(\mathrm{MnO}_2\)) will be oxidized by (\(\mathrm{KOH}\)) in the presence of an oxidizing agent, often oxygen, to form potassium manganate, (\(\mathrm{K}_2\mathrm{MnO}_4\)). This compound is known for its characteristic green color.
03

Evaluate the Options

Now that we've determined the product of the reaction is (\(\mathrm{K}_2\mathrm{MnO}_4\)) with a green color, we compare this to the given options: (a) (\(\mathrm{K}_2\mathrm{MnO}_4\)), purple green; (b) (\(\mathrm{KMnO}_4\)), purple; (c) (\(\mathrm{Mn}_2\mathrm{O}_3\)), brown; (d) (\(\mathrm{Mn}_3\mathrm{O}_4\)), black. Only option (a) correctly identifies the product and its color.
04

Confirm and Conclude

Option (a) (\(\mathrm{K}_2\mathrm{MnO}_4\)) is indeed the correct answer, as this is the product formed by the fusion of (\(\mathrm{MnO}_2\)) with (\(\mathrm{KOH}\)) under oxidizing conditions, and it is known to be green in color.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Oxidation Reactions
In chemistry, oxidation reactions are essential as they involve the transfer of electrons from one molecule to another. When we talk about oxidation, we refer to the process where an element loses electrons.
This typically results in an increase in the oxidation state of that element.

An interesting example of an oxidation reaction is the interaction between manganese dioxide (\( \mathrm{MnO}_2 \)) and potassium hydroxide (\( \mathrm{KOH} \)). ### Understanding the ReactionWhen \( \mathrm{MnO}_2 \) is fused with \( \mathrm{KOH} \), an oxidizing agent, typically oxygen, is present.
This leads to the manganese ion in \( \mathrm{MnO}_2 \) being further oxidized.
Manganese originally has an oxidation state of +4 in \( \mathrm{MnO}_2 \), but during the reaction, this state increases due to the loss of electrons.

The result of this process is the formation of potassium manganate (\( \mathrm{K}_2\mathrm{MnO}_4 \)).
This compound has manganese in a +6 oxidation state, showcasing the higher oxidation level achieved by the electron transfer.
  • Oxidation = Loss of electrons
  • Oxidizing agents help facilitate electron transfer
  • Manganese oxidation state increases from +4 to +6
Potassium Manganate
Potassium manganate (\( \mathrm{K}_2\mathrm{MnO}_4 \)) is the product of the oxidation reaction between \( \mathrm{MnO}_2 \) and \( \mathrm{KOH} \). This compound is a significant example in manganese chemistry due to its unique properties.
Let's delve into what makes it noteworthy.### Characteristics and UsesPotassium manganate is known for its striking green color, a direct result of its molecular structure and electronic transitions.
As an oxidizing agent itself, \( \mathrm{K}_2\mathrm{MnO}_4 \) can partake in further reactions, often being reduced back into manganese dioxide or transformed into potassium permanganate (\( \mathrm{KMnO}_4 \)).

This compound’s ability to change color makes it valuable for chemical tests and synthesis processes.
  • Characteristic green color
  • Forms basis for further reactions
  • Used in chemical analysis

In industrial applications, potassium manganate assists in organic synthesis and in some cases, removes impurities from solutions.
This highlights its versatility beyond just being a chemical curiosity.
Coloured Compounds
Coloured compounds, such as potassium manganate, are fascinating due to the visual clues they provide about chemical composition and reaction dynamics.
The color of a compound often arises from electronic transitions within its molecules. ### How Colours ManifestThe green color in potassium manganate is caused by the d-d electron transitions within the manganese atom.
These transitions occur when an electron moves between d-orbitals of different energy levels, absorbing specific wavelengths of light.
The wavelengths of light that are not absorbed are what we see as the compound's color.

Manganese compounds display a range of colors due to the various oxidation states manganese can adopt.
  • Potassium manganate: Green due to \( \mathrm{Mn}^{6+} \)
  • Potassium permanganate: Purple due to \( \mathrm{Mn}^{7+} \)
  • Manganese dioxide (\( \mathrm{MnO}_2 \)): Brown

The study of these colors aids in understanding the electronic structure and the nature of the elements involved in the complex reactions.

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Most popular questions from this chapter

The number of unpaired electrons present in \(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{4-}\) and \(\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\) are, respectively (a) 0,0 (b) 0,4 (c) 1,2 (d) 2,4Among the following four sets, the one having the same geometry and same magnetic property for both complexes is (a) \(\left[\mathrm{Co}\left(\mathrm{CN}_{6}\right)\right]^{3-}\) and \(\left[\mathrm{CoF}_{6}\right]^{3-}\) (b) \(\left[\mathrm{Mn}(\mathrm{CN})_{6}\right]^{3-}\) and \(\left[\mathrm{MnF}_{6}\right]^{3-}\) (c) \([\mathrm{Cr}(\mathrm{CN})]^{3-}\) and \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}\) (d) \(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{4-}\) and \(\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\)

The correct order of ionic radii of \(\mathrm{Y}^{3+}, \mathrm{La}^{3+}, \mathrm{Eu}^{3+}\) and \(\mathrm{Lu}^{3+}\) is (a) \(\mathrm{Lu}^{3+}<\mathrm{Eu}^{3+}<\mathrm{La}^{3+}<\mathrm{Y}^{3+}\) (b) \(\mathrm{La}^{3+}<\mathrm{Eu}^{3+}<\mathrm{Lu}^{3+}<\mathrm{Y}^{3+}\) (c) \(\mathrm{Y}^{3+}<\mathrm{La}^{3+}<\mathrm{Eu}^{3+}<\mathrm{Lu}^{3+}\) (d) \(\mathrm{Y}^{3+}<\mathrm{Lu}^{3+}<\mathrm{Eu}^{3+}<\mathrm{La}^{3+}\)

Which of the following compounds is expected to be coloured? (a) \(\mathrm{Ag}_{2} \mathrm{SO}_{4}\) (b) \(\mathrm{CuF}_{2}\) (c) \(\mathrm{MgF}_{2}\) (d) \(\mathrm{CuCl}\)

An aqueous solution of \(\left[\mathrm{Ti}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}\) ion has a mild violet colour of low intensity. Which of the following statements is incorrect? (a) The colour results from an electronic transition of one electron from the \(t_{2}\) to an \(\mathrm{e}_{e}\) orbital (b) The ion absorbs visible light in the region of \(\sim 5000 \AA\) (c) The transition is the result of metal-ligand back bonding (d) The low colour intensity is because of a low probability of transition

The outer electron configuration of Gd (atomic number \(=64\) ) is: (a) \(4 f^{7} 5 \mathrm{~d}^{1} 6 \mathrm{~s}^{2}\) (b) \(4 \mathrm{f}^{3} 5 \mathrm{~d}^{2} 6 \mathrm{~s}^{2}\) (c) \(4 \mathrm{f}^{5} 5 \mathrm{~d}^{0} 6 \mathrm{~s}^{2}\) (d) \(4 \mathrm{f}^{4} 5 \mathrm{~d}^{4} 6 \mathrm{~s}^{2}\)
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