CBSE Class 11 Chemistry Redox Reaction Worksheet

Question. 2CuI → Cu +CuI₂ the reaction is:
a. Redox
b. Neutralisation
c. Oxidation
d. Reduction
Answer : A

Question. H₂S reacts with halogens, the halogens:
a. Form sulphur halides
b. Are oxidised
c. Are reduced
d. None of these
Answer : C

Question. H₂O₂ reduces K₄Fe(CN)₆ :
a. In neutral solution
b. In acidic solution
c. In non-polar solvent
d. In alkaline solution
Answer : B

Question. Which halide is not oxidised by MnO₂ ?
a. F
b. Cl
c. Br
d. I
Answer : A

Question. Oxidation number of N in HNO₃ is:
a. – 3.5
b. + 3.5
c. – 3, +5
d. + 5
Answer : D

Question. The oxidation number of Mn in MnO⁻¹₄ is:
a. + 7
b. – 5
c. + 6
d. + 5
Answer : A

Question. The compound(s) behaving both oxidizing as well as reducing agent is/are:
a. H₂O₂
b. SO₂
c. HNO₂
d. HNO₃
Answer : A, B, D

Question. When Fe²⁺ changes to Fe³⁺ in a reaction?
a. It loses an electron
b. It gains an electron
c. It loses a proton
d. It gains a proton
Answer : A

Question. In acid solution, the reaction MnO^-₄ → Mn²⁺ involves:
a. Oxidation by 3 electrons
b. Reduction by 3 electrons
c. Oxidation by 5 electrons
d. Reduction by 5 electrons
Answer : D

Question. When iron or zinc is added to CuSO₄ solution, copper is precipitated. It is due to?
a. Oxidation of 2 Cu⁺²
b. Reduction of 2 Cu⁺²
c. Hydrolysis of 4 CuSO₄
d. Ionization of 4 CuSO₄
Answer : B

Question. The reaction H₂S₂+H₂O₂ → 2H₂O+S shows:
a. Oxidizing action of H₂O₂
b. Reducing action of H₂O₂
c. Alkaline nature of H₂O₂
d. Acidic nature of H₂O₂
Answer : A

Question. Which of the following is not a reducing agent?
a. NaNO₂
b. NaNO₃
c. HI
d. SnCl₂
Answer : B

Question. The compound in which the same element possesses two different oxidation states is/are:
a. bleaching powder
b. hypo
c. perdisulphuric acid
d. potassium permanganate
Answer : A, B, C

Question. Which of the following cannot work as oxidising agent?
a. O₂
b. KMnO₄
c. I₂
d. None of these
Answer : C

Assertion and Reason

Note: Read the Assertion (A) and Reason (R) carefully to mark the correct option out of the options given below:
a. If both assertion and reason are true and the reason is the correct explanation of the assertion.
b. If both assertion and reason are true but reason is not the correct explanation of the assertion.
c. If assertion is true but reason is false.
d. If the assertion and reason both are false.
e. If assertion is false but reason is true.

Question. Assertion: The oxidation numbers are artificial; they are useful as a ‘book-keeping’ device of electrons in reactions.
Reason: The oxidation numbers do not usually represent real charges on atoms, they are simply conventions that indicate what the maximum charge could possibly be on an atom in a molecule.
Answer : A

Question. Assertion: H₂ SO₄ cannot act as reducing agent.
Reason: Sulphur cannot increase its oxidation number beyond + 6.
Answer : A

Question. Assertion: Equivalent weight of NH₃ in the reaction N₂ → NH₃ is 17/3 while that of N₂ is 28/6.
Reason: Equivalent weight = Molecular weight/number of e¯ lost or gained
Answer : A

Question. Assertion: SO₂ and Cl₂ both are bleaching agents.
Reason: Both are reducing agents.
Answer : C

Question. Assertion: Fluorine exists only in −1 oxidation state.
Reason: Fluorine has 2s² 2p⁵ configuration.
Answer : B

Question. Assertion: Stannous chloride is a powerful oxidising agent which oxidises mercuric chloride to mercury.
Reason: Stannous chloride gives grey precipitate with mercuric chloride, but stannic chloride does not do so
Answer : C

Question. Assertion: HClO₄ is a stronger acid than HClO₃.
Reason: Oxidation state of Cl in HClO₄ is +VII and in HClO₃ + V.
Answer : B

Question. Assertion: In a reaction Zn(s) + CuSO₄ (aq) → ZnSO₄ (aq) + Cu(s), Zn is a reductant but itself get oxidized.
Reason: In a redox reaction, oxidant is reduced by accepting electrons and reductant is oxidized by losing electrons.
Answer : A

Question. Assertion: Oxidation number of carbon in CH₂O is zero.
Reason: CH₂O formaldehyde, is a covalent compound.
Answer : B

Question. Assertion: A reaction between Fe and 2 I occurs, but a reaction between Fe²⁺ and I⁻ does not occur.
Reason: Fe is a better reducing agent than I .
Answer : A

Comprehension Based

Paragraph–I

Consider the following unbalanced redox reaction: H₂O + AX+ BY → HA + OY + X₂B
The oxidation number of X is −2, and neither X nor water is involved in the redox process.

Question. The element(s) undergoing oxidation is/are:
a. A
b. B
c. Y
d. B or Y or both
Answer : D

Question. The possible oxidation state of B and Y in BY are, respectively:
a. +1, −1
b. +2, − 2
c. +3, − 3
d. All of these
Answer : D

Question. If the above reaction is balanced with smallest whole number coefficients, the sum of the stoichiometric coefficients of all the compounds is:
a. 9
b. 8
c. 7
d. 6
Answer : B

Paragraph–II

Oxidation reaction involves loss of electrons, and reduction reaction involves gain of electrons. The reaction in which a species disproportionate into two oxidation states (lower and higher) is called disproportionation reaction

Question. Which of the following statements is wrong?
a. A acidified K₂Cr₂O₇ paper on being exposed to SO₂ turns green.
b. Mercuric chloride and stannous chloride cannot exist as such.
c. Iron turning on addition to CuSO₄ solution decolourises the blue colour.
d. [CuI₄]²⁻ is formed but [CuCl₄]²⁻ is not.
Answer : D

Question. Which of the following statements is wrong?
a. Accidified KMnO₄ solution decolourieses on the addition of sodium oxalate.
b. In the reaction between Br₂ and CsI, Br₂ is an oxidising agent and CsI is a reducing agent.
c. In the reaction 2K₂S₂O₃ + I₂ → 2KI + K₂S₄O₆₊ , the change in the oxidation number of S is 0.5
d. C has the same oxidation number in both CH₄ and CO₂
Answer : D

Question. Which of the following statements is correct?
a. An element in the lowest oxidation state acts only as a reducing agent.
b. An element in the highest oxidation sate acts only as a reducing agent.
c. The oxidation number of V in Rb₄K(HV₁₀O₂₈) is +4.
d. The oxidation number and valency of Hg in calomel is +1
Answer : A

Question. Which of the following statements is wrong?
a. The algebraic sum of the oxidation numbers of all atoms in an ion is zero
b. The oxidation number is an arbitrary number. It can have positive, negative, zero, or fractional values.
c. When a negative ion changes to neutral species, the process is oxidation.
d. The oxidation number of phosphorous can very form –3 to +5.
Answer : A

Question. Which of the following is not a disproportionation reaction?
a. OH^- + Br₂ → Br^- + BrO^-₃ 
b. Cu₂O + 2H⁺  → Cu + Cu²⁺ +  H₂O
c. (CN)- → CO₃^2- + NO^-₃ 
d. (CN)₂ + 2OH → CN^- + CNO^- + H₂O
Answer : C

Integer

Question. Find out the value of n in MnO^-₄ + 8H⁺ + ne → Mn⁺² + 4H₂O
Answer : 5

Question. One mole of N₂H₄ loses 10 mole electrons to form a new compound Y. Assuming that all the N₂ appears in new compound, what is oxidation state of N in Y? There is no change in oxidation state of H.
Answer : 3

Question. The equivalent weight of HNO₃ (molecular weight = 63) in the following reaction is 3Cu + 8HNO₃ → 3Cu(NO₃)₂ + 2NO + 4H₂O
Answer : 84

Question. In the following reaction xZn + yHNO₃ (dil) → aZn(NO₃)₃ + bH₂O + cNH₄NO₃
What is the sum of the coefficients (a + b + c) ?
Answer : 8

Question. CN⁻ ion is oxidized by a powerful oxidising agent of NO⁻₃ and CO₂ or CO₃²⁻ depending on the acidity of the reaction mixture CN⁻ → CO₂ + NO⁻₃ + H⁺ + ne⁻
What is the number (n) of electrons involved in the process, divided by 10?
Answer : 3

Instructions:

1. All questions are compulsory.

2. Please give the explanation for the answer where applicable.

Q1 - Name the oxidiser and reducer in the following reaction:-

SnCl2 + 2FeCl3 SnCl4 + 2FeCl2 (1 Mark)

Q2 - Define oxidation number and calculate the oxidation number of Cr in K2Cr2O7. (2 Marks)

Q3 - What is the usual oxidation state of oxygen? In which type of compounds oxygen shows an oxidation no. of -1 and +2? (1 Mark)

Q4 - What is meant by half reaction? (1 Mark)

Q5 - Balance the following equation in the acidic medium by oxidation number method. (5 Marks)

Q6 - Write the half reactions for the following Redox reaction;-

(a) 2Fe3+(aq) +2I-(aq) 2Fe2+(aq) + I2(aq)

(b) Zn(s) + 2H+(aq) Zn2+(aq) + H2(g) (2 Marks)

Q7 - Identify the strongest and the weakest reducing agents from the following metals:- Zn, Cu, Ag, Na (2 Marks)

Q8 - The standard reduction potential for Cu2+/Cu is +0.34 V. Calculate the standard reduction potential at pH =14 for the above couple Ksp of Cu(OH)2 is 1.0X10-19. (3 Marks)

Q9 - Calculate pH of the following half cell Pt, H2/H2SO4. The oxidation potential is +0.3 V. (3 Marks)

Q1. Explain the terms: oxidation & reduction in terms of electrons. Give one e.g. n each case.

Q2. Define the terms: - oxidizing agent & reducing agent according to electronic concept. Give one e.g. in each case.

Q3. What are redox reactions? Give one e.g.

Q4. Explain what happens when a zinc rod is dipped in CuSO4 solu.

Q5. Write the following redox reactions using half equations:- (a) Zn + PbCl2 → Pb + ZnCl2
(b) 2Fe+3 + 2I- → I2 + 2Fe+2 (c) 2Na + Cl2 → 2NaCl (d)Mg + Cl2 → MgCl2 (e) Zn + 2H+ → ZN+2 + H2

Q6. Define oxidation number. Write general rules of assigning oxidation numbers to various atoms in ions & molecules.

Q7. Explain the terms: - (1) oxidation (2) Reduction (3) Oxidising agent (4) Reducing agent in terms of oxidation number. Give two e.g. to illustrate your answer:-

Q8. Discuss the following redox reactions:- (a) Combination reactions (b) Decomposition reactions
(c) Metals & Non-Metals displacement reactions (d) Disproportionation reaction. Give one e.g. in each case.

Q9. Draw a labelled diagram for the Daniel cell. Discuss its working.

Q10. Discuss briefly the function of the salt bridge in an electrochemical cell.

Q11. What is the oxidation No. of (i) C in CH2O (ii) H in [Pt(C2H4)Cl3] (iii) N in HNO3

Q12. Identify the oxidizing agent, reducing agent, substances oxidized & reduced in the following reactions;-
(i) MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O (ii) 2MnO4- + 10Cl-1 16H+ → 7Mn+2 ⊥ < 10

Q13. Justify that the reaction:- 2Cu2O + Cu2S → 6Cu + SO2 is a redox reaction.
Identify the species oxidized, reduced, which acts as oxidant & which acts as reductant?

Q14. Find out the oxidation number of underline atoms in the following species :- PbSO4, BrF3, CrO4-2, MnO4, Sb2O5, (NH4)2SO4, C6H12O6, CH4, Cr2O7-2, Na2S4O6, H2S2O8

Q15. Which of the following species, do not show disproportion reaction and why?
ClO-, ClO2-, ClO3- & ClO4-
Also write reaction for each species that disproportionate.