A sample of steel weighing 0 . 6 g and containing S as an impurity was burnt in a stream of O 2 , when S was converted to its oxide SO 2 · SO 2 was then oxidized to SO 4 - - by using H 2 O 2 solution containing 30 mL of 0 . 04 M NaOH . 22 . 48 mL of 0 . 024 M HCl was required to neutralize the base remaining after oxidation. Calculate the % of S in the sample:

Given: weight of the sample = 0 . 6 g , NaOH = 0 . 04 M , HCl = 0 . 024 4 OH - + 2 H 2 O + SO 2 ⟶ SO 4 2 - + 4 H 2 O + 2 e - 4 OH - + SO 2 ⟶ SO 4 2 - + 2 H 2 O + 2 e - … 1 (Balanced chemical reaction) 2 H 2 O + H 2 O 2 + 2 e - ⟶ 2 H 2 O + 2 OH - H 2 O 2 + 2 e - ⟶ 2 OH - . . . 2 (Balanced chemical reaction) Eq . 1 + 2 2 OH - + H 2 O 2 + SO 2 ⟶ SO 4 2 - + 2 H 2 O … 3 ∵ NaOH + HCl ⟶ NaCl + H 2 O gm Eq . = Normality × volume gm Eq . of NaOH = 0 . 04 × 30 × 10 - 3 = 1 . 2 × 10 - 3 gm Eq . of HCl = 0 . 024 × 22 . 48 × 10 - 3 = 0 . 53952 × 10 - 3 gm Eq . of unneutralized NaOH = 1 . 2 - 0 . 53952 × 10 - 3 = 0 . 66048 × 10 - 3 From equation 3 2 OH - + H 2 O 2 + SO 2 ⟶ SO 4 2 - + 2 H 2 O Moles of sulfate ion or sulfur = Moles of NaOH 2 ( By Stoichiometry of this reaction ) n S = 0 . 66048 × 10 - 3 2 = 0 . 33024 × 10 - 3 ∴ moles of S = 0 . 33024 × 10 - 3 mole = wt . atomic wt . 0 . 33024 × 10 - 3 = wt . 32 wt . = 10 . 5676 × 10 - 3 gm % of S sample = 10 . 5676 × 10 - 3 0 . 6 × 100 = 1 . 76 % Hence % of S in the sample is 1 . 76 %

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 %

HARD

JEE Main/Advance

IMPORTANT

Earn 100

$2.5 g$ of mixture of crystalline oxalic acid $(H_{2} C_{2} O_{4} . 2 H_{2} O)$ and sodium oxalate $({Na}_{2} C_{2} O_{4})$ was dissolved in $100 mL$ of water. $50 mL$ of this solution was titrated against $\frac{N}{10 NaOH}$ solution when $119.05 mL$ of the base was found necessary to reach the end point with phenolphthalein as the indicator. $1 g$ of the mixture was dissolved in water and the solution titrated against $\frac{N}{10 {KMnO}_{4}}$ in the presence of dil. $H_{2} {SO}_{4}$ . What is the volume of ${KMnO}_{4}$ needed for getting the end point with $0.5 g$ of the mixture?

Important Questions on Redox Reactions

HARD

JEE Main/Advance

IMPORTANT

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

0.6213 g

of sample contains an unknown amount of

{As}_{2} O_{3}

. The sample was treated with

HCl

resulting information of

{AsCl}_{3} (g)

which was distilled into a beaker of water. The hydrolysis reaction is as follows:

{AsCl}_{3} + 2 H_{2} O \to {HAsO}_{2} + 3 H^{+} + 3 {Cl}^{-}

The amount of

{HAsO}_{2}

was determined by titration with

H_{2} C_{2} O_{4} . 2 H_{2} O = \frac{0.3 \times 2}{126}

, requiring

23.04 mL

to reach the equivalence point. The redox products in the titration were

H_{3} {AsO}_{4}

and

I

. Find the amount of

{KMnO}_{4}

needed to oxidize

As

{As}_{2} O_{3}

to its maximum possible oxidation state in acidic medium.

HARD

JEE Main/Advance

IMPORTANT

Beta Question Bank for Engineering: Chemistry>Chapter 6 - Redox Reactions>EXERCISE-4>Q 5

A sample of steel weighing

0.6 g

and containing

S

as an impurity was burnt in a stream of

O_{2}

, when

S

was converted to its oxide

{SO}_{2} \cdot {SO}_{2}

was then oxidized to

gm Eq .

by using

H_{2} O_{2}

solution containing

30 mL

0.04 M NaOH . 22.48 mL

0.024 M HCl

was required to neutralize the base remaining after oxidation. Calculate the

%

S

in the sample:

EASY

JEE Main/Advance

IMPORTANT

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

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

{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

%

{Mn}_{3} O_{4}

in the sample?

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

{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

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.

Important Questions on Redox Reactions

Learn and Prepare for any exam you want !