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D and F Block Elements question

2019 · 11 Jan · Shift 2 · Q16
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D and F Block Elements question

2019 · 11 Jan · Shift 2 · Q16

JEE MainChemistryD and F Block ElementsMCQ+4 / −1
A‾  →4KOH,O2  2B‾(Green)  +  2H2O3B‾  →4HCl  2C‾(Purple)  +  MnO2+2H2O2C‾  →H2O.KI  2A‾(Purple)  +  2KOH  +  D‾\underline A \,\,\xrightarrow{4KOH,{O_2}} \,\,\mathop {2\underline B }\limits_{\left( {Green} \right)} \,\, + \,\,2{H_2}O3\underline B \,\,\xrightarrow{4HCl} \,\,\mathop {2\underline C }\limits_{\left( {Purple} \right)} \,\, + \,\,Mn{O_2} + 2{H_2}O2\underline C \,\,\xrightarrow{{H_2}O.KI} \,\,\mathop {2\underline A }\limits_{\left( {Purple} \right)} \,\, + \,\,2KOH\,\, + \,\,\underline DA​4KOH,O2​​(Green)2B​​+2H2​O3B​4HCl​(Purple)2C​​+MnO2​+2H2​O2C​H2​O.KI​(Purple)2A​​+2KOH+D​ In the above sequence of reactions, A‾{\underline A }A​ and D‾{\underline D }D​, respectively, are :
  1. A
    KlKlKl and KMnO4KMnO_4KMnO4​
  2. B
    KlKlKl and K2MnO4K_2MnO_4K2​MnO4​
  3. C
    KlO3KlO_3KlO3​ and MnO2MnO_2MnO2​
  4. D
    MnO2MnO_2MnO2​ and KlO3KlO_3KlO3​
View written solutionFree

Correct answer: D

  1. Identify the manganese species from the colors
  • Green manganese compound in alkaline medium is typically potassium manganate, K2MnO4K_2MnO_4K2​MnO4​.
  • Purple manganese compound is potassium permanganate, KMnO4KMnO_4KMnO4​.

So,

B=K2MnO4,C=KMnO4B = K_2MnO_4, \qquad C = KMnO_4B=K2​MnO4​,C=KMnO4​
  1. Use the first reaction to identify AAA

Given:

A→O24KOH2B+2H2OA \xrightarrow[O_2]{4KOH} 2B + 2H_2OA4KOHO2​​2B+2H2​O

Substituting B=K2MnO4B = K_2MnO_4B=K2​MnO4​:

A→O24KOH2K2MnO4+2H2OA \xrightarrow[O_2]{4KOH} 2K_2MnO_4 + 2H_2OA4KOHO2​​2K2​MnO4​+2H2​O

This is the well-known preparation of manganate from manganese dioxide:

2MnO2+4KOH+O2→2K2MnO4+2H2O2MnO_2 + 4KOH + O_2 \rightarrow 2K_2MnO_4 + 2H_2O2MnO2​+4KOH+O2​→2K2​MnO4​+2H2​O

Hence,

A=MnO2A = MnO_2A=MnO2​
  1. Check the second reaction

Given:

3B→4HCl2C+MnO2+2H2O3B \xrightarrow{4HCl} 2C + MnO_2 + 2H_2O3B4HCl​2C+MnO2​+2H2​O

Substitute B=K2MnO4B = K_2MnO_4B=K2​MnO4​ and C=KMnO4C = KMnO_4C=KMnO4​:

3K2MnO4+4HCl→2KMnO4+MnO2+4KCl+2H2O3K_2MnO_4 + 4HCl \rightarrow 2KMnO_4 + MnO_2 + 4KCl + 2H_2O3K2​MnO4​+4HCl→2KMnO4​+MnO2​+4KCl+2H2​O

This is the correct disproportionation of manganate in acidic medium, confirming:

B=K2MnO4,C=KMnO4B = K_2MnO_4, \quad C = KMnO_4B=K2​MnO4​,C=KMnO4​
  1. Use the third reaction to identify DDD

Given:

2C→H2O,KI2A+2KOH+D2C \xrightarrow{H_2O, KI} 2A + 2KOH + D2CH2​O,KI​2A+2KOH+D

Substitute C=KMnO4C = KMnO_4C=KMnO4​ and A=MnO2A = MnO_2A=MnO2​:

2KMnO4+KI+H2O→2MnO2+2KOH+D2KMnO_4 + KI + H_2O \rightarrow 2MnO_2 + 2KOH + D2KMnO4​+KI+H2​O→2MnO2​+2KOH+D

In neutral/alkaline medium, permanganate oxidizes iodide to iodate while itself gets reduced to MnO2MnO_2MnO2​:

2KMnO4+KI+H2O→2MnO2+KIO3+2KOH2KMnO_4 + KI + H_2O \rightarrow 2MnO_2 + KIO_3 + 2KOH2KMnO4​+KI+H2​O→2MnO2​+KIO3​+2KOH

So,

D=KIO3D = KIO_3D=KIO3​
  1. Final identification

Thus,

A=MnO2,D=KIO3A = MnO_2, \qquad D = KIO_3A=MnO2​,D=KIO3​

So the correct option is:

D: MnO2 and KIO3\boxed{\text{D: } MnO_2 \text{ and } KIO_3}D: MnO2​ and KIO3​​
  1. Comparison with stored correct answer

Stored correct answer: D

Our derived answer: D

They match.

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