1 g of a moist sample of a mixture of KClO 3 and KCl was dissolved in water and made upto 250 mL . 25 mL of this solution was treated with SO 2 to reduced chlorate into chloride and the excess SO 2 was boiled off. When the total chloride was precipitated, 0 . 1435 g of AgCl was obtained. In another experiment 25 mL of the original solution was treated with 30 mL of 0 . 2 N solution of FeSO 4 and unreacted FeSO 4 required 37 . 5 mL of 0 . 08 N solution of an oxidizing agent for complete oxidation. Calculate the molar ratio of chlorate and chloride in the given mixture. Fe 2 + reacts with ClO 3 - according to equation: ClO 3 - + 6 Fe 2 + + 6 H + → Cl - + 6 Fe 3 + + 3 H 2 O Also calculate the mass percent of moisture present in the moist sample.

Let the mass of KClO 3 be x gm Let mass of KCl be y gm mole = mass atomic mass n KClO 3 ( moles ) = x 122 . 5 n KCl = y 74 . 5 For Cl 6 e - + 6 H + + Cl + 5 O 3 - ⟶ Cl - + 3 H 2 O Valence factor = 5 - - 1 = 6 It is given that When the total chloride was precipitated, 0 . 1435 gm AgCl was obtained ⇒ n KClO 3 + n KCl = n AgCl ⇒ x 122 . 5 + y 74 . 5 = 0 . 1435 143 . 5 = 0 . 001 . . . i for complete oxidation of an oxidizing agent Milliequivalents of KClO 3 or KCl = Milliequivalents of ( reacted FeSO 4 solution - unreacted FeSO 4 solution ) gm Eq . = moles × valence factor M . eq . = Normality × Volume = N 1 V 1 - N 2 V 2 = 30 × 0 . 2 - 37 . 5 × 0 . 08 = 3 gm Eq . of KClO 3 = x ( 6 ) 122 . 5 = 0 . 003 x 122 . 5 = 0 . 0005 ( n KClO 3 ) gm Eq . of KCl = y ( 6 ) 74 . 5 = 0 . 003 y 74 . 5 = 0 . 0005 ( n KCl ) Molar ratio n KClO 3 n KCl = 1 1 moisture = 1 - mass ( KClO 3 + KCl ) = 1 - ( 122 . 5 + 74 . 5 ) × 0 . 0005 = 0 . 015 g Mass % of moisture = 0 . 015 1 × 100 = 1 . 5 % Hence, the molar ratio of KClO 3 and KCl is 1 : 1 and % of moisture is 1 . 5 %

EASY

JEE Main/Advance

IMPORTANT

Earn 100

In the presence of fluoride ion, ${Mn}^{2 +}$ can be titrated with ${MnO}_{4}^{-}$ , both reactants being converted to a complex of $Mn$ (III). A $0.545 g$ sample containing ${Mn}_{3} O_{4}$ was dissolved and all manganese was converted to ${Mn}^{2 +}$ . Titration in the presence of fluoride ion consumed $31.1 mL$ of ${KMnO}_{4}$ that was $0.177 N$ against oxalate.
(a) write a balanced chemical equation for the reaction, assuming that the complex is ${MnF}_{4}^{-}$ .
(b) what was the $%$ of ${Mn}_{3} O_{4}$ in the sample?

Important Questions on Redox Reactions

HARD

JEE Main/Advance

IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 6 - Redox Reactions>EXERCISE-4>Q 7

A mixture of two gases,

H_{2} S

and

{SO}_{2}

is passed through three beakers successively. The first beaker contains

{Pb}^{2 +}

ions, which absorbs

S^{2 -}

forming

PbS

. The second beaker contains

25 mL

0.0396 {NI}_{2}

to oxidize

{SO}_{2}

{SO}_{4}^{2 -}

. The third contains

10 mL

0.0345 N

thiosulphate solution to retain any

I_{2}

carried over from the second absorber. A

25 L

gas sample was passed through the apparatus followed by an additional amount of

N_{2}

to sweep last traces of

{SO}_{2}

from first and second absorber. The solution from the first absorber was made acidic and treated with

20 mL

0.0066 M K_{2} {Cr}_{2} O_{7}

which converted

S^{2 -}

{SO}_{2}

. The excess dichromate was reacted with solid

KI

and the liberated iodine required

7.45 mL

0.0345 N {Na}_{2} S_{2} O_{3}

solution. The solutions in the second and third absorbers were combined and the resultant iodine was titrated with

2.44 mL

of the same thiosulphate solution. Calculate the concentrations of

{SO}_{2}

and

H_{2} S

\frac{mg}{L}

of the sample :

HARD

JEE Main/Advance

IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 6 - Redox Reactions>EXERCISE-4>Q 8

1 g

of a moist sample of a mixture of

{Mn}^{2 +}

and

KCl

was dissolved in water and made upto

= \frac{1}{3} \times 2.91096 = 0.97032

of this solution was treated with

{SO}_{2}

to reduced chlorate into chloride and the excess

{SO}_{2}

was boiled off. When the total chloride was precipitated,

0.1435 g

AgCl

was obtained. In another experiment

25 mL

of the original solution was treated with

30 mL

0.2 N

solution of

{FeSO}_{4}

and unreacted

{FeSO}_{4}

required

37.5 mL

0.08 N

solution of an oxidizing agent for complete oxidation. Calculate the molar ratio of chlorate and chloride in the given mixture.

{Fe}^{2 +}

reacts with

{ClO}_{3}^{-}

according to equation:

{ClO}_{3}^{-} + 6 {Fe}^{2 +} + 6 H^{+} \to {Cl}^{-} + 6 {Fe}^{3 +} + 3 H_{2} O

Also calculate the mass percent of moisture present in the moist sample.

HARD

JEE Main/Advance

IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 6 - Redox Reactions>EXERCISE-4>Q 9

A steel sample is to be analysed for

Cr

and

Mn

simultaneously. By suitable treatment the

Cr

is oxidized to

{Cr}_{2} O_{7}^{2 -}

and the

Mn

{MnO}_{4}^{-} . A 10.00 g

sample of steel is used to produce

250.0 mL

of a solution containing

{Cr}_{2} O_{7}^{2 -}

and

{MnO}_{4}^{-} . A 10.00 mL

portion of this solution is added to

{aBaCl}_{2}

solution and by proper adjustment of the acidity, the chromium is completely precipitated as

{BaCrO}_{4}; 0.0549 g

is obtained. A second

10.00 mL

portion of this solution requires exactly

15.95 mL

0.0750 M

standard

{Fe}^{2 +}

solution for its titration (in acid solution). Calculate the

%

Mn

and

%

Cr

in the steel sample.

HARD

JEE Main/Advance

IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 6 - Redox Reactions>EXERCISE-4>Q 10

1.5 g

sample containing oxalic acid and some inert impurity was dissolved in enough water and volume made up to

250 mL

. A

20 mL

portion of this solution was then mixed with

30 mL

of an alkali solution. The resulting solution was then treated with stoichiometric amount of

{CaCl}_{2}

just needed for precipitation of oxalate as

{CaC}_{2} O_{4}

. Solution was filtered off and filtrate was finally titrated against

0.1 M HCl

solution.

8.0 mL

of acid was required to reach the equivalence point. At last, the above neutral solution was treated with excess of

{AgNO}_{3}

solution and

AgCl

obtained was washed, dried and weighed to be

0.4305 g . De -

termine mass percentage of oxalic acid in the original sample:

HARD

JEE Main/Advance

IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 6 - Redox Reactions>EXERCISE-4>Q 11

1 g

sample containing

NaOH

as the only basic substance and some inert impurity was left exposed to atmosphere for a very long time so that part of

NaOH

got converted into

{Na}_{2} {CO}_{3}

by absorbing

{CO}_{2}

from atmosphere. The resulting sample was dissolved in water and volume made upto

100 mL

. A

20 mL

portion of this solution required

16 mL 0.25 M HCl

solution to reach the equivalence point when methyl orange was used as indicator. In a separate analysis,

20 mL

portion of the same solution was taken along with phenolphthalein indicator and mixed with

50 mL

0.1 M HCl

solution. An additional

9.00 mL 0.1 M

Ba (OH)_{2}

solution was required to just restore the pink colour of solution. Determine mass percentage of

NaOH

in the original sample and mass percentage of

{Na}_{2} {CO}_{3}

in the sample after exposure to atmosphere.

EASY

JEE Main/Advance

IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 6 - Redox Reactions>EXERCISE-4>Q 12

Write balanced net ionic equation for the following reactions in acidic solution.

(a) $S_{2} O_{3}^{2 -} (aq) + {Cr}_{2} O_{7}^{2 -} (aq) ⟶ S_{4} O_{6}^{2 -} (aq) + {Cr}^{3 +} (aq)$

(b) ${ClO}_{3}^{-} (aq) + {As}_{2} S_{3} (s) ⟶ {Cl}^{-} (aq) + H_{2} {AsO}_{4}^{-} (aq) + {HSO}_{4}^{-} (aq)$

MEDIUM

JEE Main/Advance

IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 6 - Redox Reactions>EXERCISE-4>Q 13

Write balanced net ionic equations for the following reactions in basic solution :

(a) ${Tl}_{2} O_{3} (s) + {NH}_{2} OH (aq) ⟶ TlOH (s) + N_{2} (g)$

(b) $Cu {({NH}_{3})}_{4}^{2 +} (aq) + S_{2} O_{4}^{2 -} (aq) ⟶ {SO}_{3}^{2 -} (aq) + Cu (s) + {NH}_{3} (aq)$

MEDIUM

JEE Main/Advance

IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 6 - Redox Reactions>EXERCISE-4>Q 14

In a quantitative determination of iron in an ore, an analyst converted $0.40 g$ , of the ore into its ferrous. This required $40.00 mL$ of $0.1 N$ solution of ${KMnO}_{4}$ for titration.

(i) How many milliequivalents of ${KMnO}_{4}$ does $40.00 mL$ of $0.1 N$ solution represent?

(ii) How many equivalents of iron were present in the sample of the ore taken for analysis?

(iii) How many grams of iron were present in the sample?

(iv) What is the percentage of iron in the ore?

(v) What is the molarity of ${KMnO}_{4}$ solution used?

(vi) How many moles of ${KMnO}_{4}$ were used for titration ? $(Fe = 56)$

Important Questions on Redox Reactions

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