jee main chemistry important questions | d And f-Block Elements jee main questions FREE

Q 21 :
Consider the following reactions

$K_{2} {Cr}_{2} O_{7} \to_{- H_{2} O}^{KOH} [A] \to_{- H_{2} O}^{H_{2} {SO}_{4}} [B] + K_{2} {SO}_{4}$

The products [A] and [B], respectively are: [2025]

$K_{2} {CrO}_{4} and K_{2} {Cr}_{2} O_{7}$
$K_{2} {CrO}_{4} and CrO$
$K_{2} {CrO}_{4} and {Cr}_{2} O_{3}$
$K_{2} Cr {(OH)}_{6} and {Cr}_{2} O_{3}$

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(1)

Chromate $({CrO}_{4}^{2 -})$ and dichromate $({Cr}_{2} O_{7}^{2 -})$ are inter-convertible into each other depending upon the pH of the solution. In acidic medium, ${Cr}_{2} O_{7}^{2 -}$ is more stable and in basic medium, ${CrO}_{4}^{2 -}$ is more stable.

$K_{2} {Cr}_{2} O_{7} \to_{- H_{2} O}^{KOH} \underset{[A]}{K_{2} {CrO}_{4}} \to_{- H_{2} O}^{H_{2} {SO}_{4}} \underset{[B]}{K_{2} {Cr}_{2} O_{7}} + K_{2} {SO}_{4}$

Q 22 :
Preparation of potassium permanganate from ${MnO}_{2}$ involves a two-step process in which the first step is a reaction with $KOH$ and ${KNO}_{3}$ to produce [2025]

$K_{2} {MnO}_{4}$
$K_{3} {MnO}_{4}$
${KMnO}_{4}$
$K_{4} [Mn {(OH)}_{6}]$

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(1)

Potassium permanganate is prepared by fusion of ${MnO}_{2}$ (pyrolusite) with an alkali metal hydroxide and an oxidising agent. This produces the dark green $K_{2} {MnO}_{4}$ , which disproportionates in a neutral or acidic solution to give permanganate.

${MnO}_{2} + 2 KOH + {KNO}_{3} \to K_{2} {MnO}_{4} + {KNO}_{2} + H_{2} O$

$3 {MnO}_{4}^{2 -} + 4 H^{+} \to 2 {MnO}_{4}^{-} + {MnO}_{2} + 2 H_{2} O$

Q 23 :
Which of the following oxidation reactions are carried out by both $K_{2} {Cr}_{2} O_{7}$ and ${KMnO}_{4}$ in acidic medium? [2025]

(A)   $I^{-} \to I_{2}$

(B)    $S^{2 -} \to S$

(C)   ${Fe}^{2 +} \to {Fe}^{3 +}$

(D)   $I^{-} \to {IO}_{3}^{-}$

(E)   $S_{2} O_{3}^{2 -} \to {SO}_{4}^{2 -}$

Choose the correct answer from the options given below:

(C), (D) and (E) only
(A), (B) and (C) only
(B), (C) and (D) only
(A), (D) and (E) only

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(2)

Reactant	Product with acidic ${KMnO}_{4}$	Product with faintly alkaline ${KMnO}_{4}$	Product with acidic $K_{2} {Cr}_{2} O_{7}$
$I^{-}$	$I_{2}$	${IO}_{3}^{-}$	$I_{2}$
$S^{2 -}$	$S$	$S$	$S$
${Fe}^{2 +}$	${Fe}^{3 +}$	${Fe}^{3 +}$	${Fe}^{3 +}$
$S_{2} O_{3}^{2 -}$	${SO}_{4}^{2 -} + S$	${SO}_{4}^{2 -}$	${SO}_{4}^{2 -} + S$

Q 24 :
The amphoteric oxide among $V_{2} O_{3}, V_{2} O_{4}$ and $V_{2} O_{5}$ , upon reaction with alkali leads to formation of an oxide anion. The oxidation state of V in the oxide anion is: [2025]

+4
+7
+3
+5

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(4)

$V_{2} O_{3}$ – basic, $V_{2} O_{4}$ – less basic, $V_{2} O_{5}$ – amphoteric. $V_{2} O_{5}$ reacts with alkalies as well as acids to give ${VO}_{4}^{3 -}$ and ${VO}_{4}^{+}$ respectively. Oxidation number of V in ${VO}_{4}^{3 -}$ is +5.

Q 25 :
The molar mass of the water insoluble product formed from the fusion of chromite ore $({FeCr}_{2} O_{4})$ with ${Na}_{2} {CO}_{3}$ in presence of $O_{2}$ is ______ g ${mol}^{- 1}$ . [2025]

0%

(160)

$4 {FeCr}_{2} O_{4} + 8 {Na}_{2} {CO}_{3} + 7 O_{2} \to 8 {Na}_{2} {CrO}_{4} + 2 {Fe}_{2} O_{3} + 8 {CO}_{2}$

${Fe}_{2} O_{3}$ is insoluble in water. Its molar mass $= [2 \times 56 + 3 \times 16]$ $g/mol$

$= 160 g/mol$

Topic Question Set

Q 21 :
Consider the following reactions

$K_{2} {Cr}_{2} O_{7} \to_{- H_{2} O}^{KOH} [A] \to_{- H_{2} O}^{H_{2} {SO}_{4}} [B] + K_{2} {SO}_{4}$

The products [A] and [B], respectively are: [2025]

Q 22 :
Preparation of potassium permanganate from ${MnO}_{2}$ involves a two-step process in which the first step is a reaction with $KOH$ and ${KNO}_{3}$ to produce [2025]

Q 24 :
The amphoteric oxide among $V_{2} O_{3}, V_{2} O_{4}$ and $V_{2} O_{5}$ , upon reaction with alkali leads to formation of an oxide anion. The oxidation state of V in the oxide anion is: [2025]

Q 25 :
The molar mass of the water insoluble product formed from the fusion of chromite ore $({FeCr}_{2} O_{4})$ with ${Na}_{2} {CO}_{3}$ in presence of $O_{2}$ is ______ g ${mol}^{- 1}$ . [2025]

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Topic Question Set

Q 21 : Consider the following reactions K2Cr2O7→-H2OKOH[A]→-H2OH2SO4[B]+K2SO4 The products [A] and [B], respectively are: [2025]

Q 22 : Preparation of potassium permanganate from MnO2 involves a two-step process in which the first step is a reaction with KOH and KNO3 to produce [2025]

Q 23 : Which of the following oxidation reactions are carried out by both K2Cr2O7 and KMnO4 in acidic medium? [2025] (A) I-→I2 (B) S2-→S (C) Fe2+→Fe3+ (D) I-→IO3- (E) S2O32-→SO42- Choose the correct answer from the options given below:

Q 24 : The amphoteric oxide among V2O3, V2O4 and V2O5, upon reaction with alkali leads to formation of an oxide anion. The oxidation state of V in the oxide anion is: [2025]

Q 25 : The molar mass of the water insoluble product formed from the fusion of chromite ore (FeCr2O4) with Na2CO3 in presence of O2 is ______ g mol-1. [2025]

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Q 21 :
Consider the following reactions

$K_{2} {Cr}_{2} O_{7} \to_{- H_{2} O}^{KOH} [A] \to_{- H_{2} O}^{H_{2} {SO}_{4}} [B] + K_{2} {SO}_{4}$

The products [A] and [B], respectively are: [2025]

Q 22 :
Preparation of potassium permanganate from ${MnO}_{2}$ involves a two-step process in which the first step is a reaction with $KOH$ and ${KNO}_{3}$ to produce [2025]

Q 24 :
The amphoteric oxide among $V_{2} O_{3}, V_{2} O_{4}$ and $V_{2} O_{5}$ , upon reaction with alkali leads to formation of an oxide anion. The oxidation state of V in the oxide anion is: [2025]

Q 25 :
The molar mass of the water insoluble product formed from the fusion of chromite ore $({FeCr}_{2} O_{4})$ with ${Na}_{2} {CO}_{3}$ in presence of $O_{2}$ is ______ g ${mol}^{- 1}$ . [2025]