Q128P - Chemistry: Molecular Nature Of Matter And Change

Question

Dark green manganate salts contain the  $Mn{O_4}^{2-}$ ion. The ion is stable in basic solution but disproportionates in acid to $Mn{O}_2\left(s\right)$  and $Mn{O_4}^{-}$.

(a) What is the oxidation state of$Mn$in $Mn{O_4}^{-}$, and  $Mn{O}_2$? 

(b) Write a balanced equation for the reaction of   in acidic solution.1

Step-by-Step Solution

Answer

1. The oxidation state of MN in $Mn{O_4}^{2-}$  is +6  , in $Mn{O_4}^{-}$  is  +7 and in  $Mn{O}_2$ is  +4 .
2. The balanced chemical reaction is given by

      $2e^{-} + Mn{{O_4}^{2-}}_{\left(aq\right)}+ 4{H^{+}}_{\left(aq\right)} Mn{O}_{2\left(s\right)}+ 2H_2{O}_{\left(l\right)}$

Step 1: Given information

The composition of dark green manganate salt is  $Mn{O_4}^{2-}$ ions. This ion stays stable in the basic solution but shows disproportion reaction in acidic solution of $Mn{O_4}^{-}$  and  $Mn{O}_2$  .

Step 2: Definition of the oxidation process and the loss of oxygen atoms involved in the process

 

The loss of electrons during a chemical reaction which a molecule, atom or ion undergoes is known as oxidation.

The electrons are taken up by  $Mn{O_4}^{2-}$ as it is reduced to $Mn{O}_2$  in the presence of an acid. The reaction involves losing of two oxygen atoms and this produces water molecules with protons in solution.

 

Step 3: The oxidation state of f o r M n O 4 2 -

(a)The oxidation state of $Mn$ for $Mn{O_4}^{2-}$  is given by:

The overall charge is  -2  .

The charge of each oxygen atom is also -2   .

The charge of   is calculated as:

 $$\begin{gathered} =-2-4(-2) \\ =-2+8 \\ =+6 \end{gathered}$$

Step 4: The oxidation state of M n for M n O 4 -

The oxidation state of $Mn$ for $Mn{O_4}^{-}$  is given by:

The overall charge is  -1    .

The charge of each oxygen atom is also   -2 .

The charge of   is calculated as:

 $$\begin{gathered} =-1-4(-2) \\ =-1+8 \\ =+7 \end{gathered}$$

Step 5: The oxidation state of M n f o r   M n O 2

The oxidation state of $Mn$ for $Mn{O}_2$  is given by:

The overall charge is  0  .

The charge of each oxygen atom is also  -2  .

The charge of   is calculated as:

 $$\begin{gathered} =0-2(-2) \\ =0+4 \\ =+4 \end{gathered}$$

Step 6: The chemical reaction involved in acidic solution

c) The reaction for this is given by:

 ­$2e^{-}+ Mn{{O_4}^{2-}}_{\left(aq\right)} + 4{H^{+}}_{\left(aq\right)}\to Mn{O}_{2\left(s\right)} + 2H_2{O}_{\left(l\right)}$