Class 11 Chemistry - Chapter Redox Reactions NCERT Solutions | Why does the following reaction occur ?

Balance the following redox reactions by ion – electron method :

(a) MnO₄ ^– (aq) + I ^– (aq) → MnO_{2 (s)} + I_2(s) (in basic medium)

(b) MnO₄ ^– (aq) + SO_{2 (g)} → Mn²⁺ (aq) + HSO₄^– (aq) (in acidic solution)

(c) H₂O_{2 (aq)} + Fe ²⁺ (aq) → Fe³⁺ (aq) + H₂O (l) (in acidic solution)

(d) Cr₂O₇ ^2– + SO_2(g) → Cr³⁺ _(aq) + SO₄^2– (aq) (in acidic solution)

Assign oxidation number to the underlined elements in each of the following species:

(a) NaH₂PO₄

(b) NaHSO₄

(c) H₄P₂O₇

(d) K₂MnO₄

(e) CaO₂

(f) NaBH₄

(g) H₂S₂O₇

(h) KAl(SO₄)₂.12 H₂O

What are the oxidation number of the underlined elements in each of the following and how do you rationalise your results ?

(a) KI₃

(b) H₂S₄O₆

(c) Fe₃O₄

(d) CH₃CH₂OH

(e) CH₃COOH

Justify that the following reactions are redox reactions:

(a) CuO_(s) + H_2(g) → Cu_(s) + H₂O_(g)

(b) Fe₂O_3(s) + 3CO_(g) → 2Fe_(s) + 3CO_2(g)

(c) 4BCl_3(g) + 3LiAlH_4(s) → 2B₂H_6(g) + 3LiCl_(s) + 3 AlCl_{3 (s)}

(d) 2K_(s) + F_2(g) → 2K⁺F^– _(s)

(e) 4 NH_3(g) + 5 O_2(g) → 4NO_(g) + 6H₂O_(g)

Balance the following equations in basic medium by ion-electron method and oxidation number methods and identify the oxidising agent and the reducing agent.

(a) P_4(s) + OH ^– _(aq)  →  PH_3(g) + HPO^{2 –} _(aq)

(b) N₂H_4(l) + ClO^{3 –} _(aq)  →  NO_(g)  +  Cl^–_(g)

(c) Cl₂O_{7 (g)}  +  H₂O_2(aq)  →  ClO ^– _2(aq)   +  O_2(g)  +  H ⁺ _(aq)

Fluorine reacts with ice and results in the change:

H₂O_(s) + F_2(g) → HF_(g) + HOF_(g)

Justify that this reaction is a redox reaction.

Write the formulae for the following compounds:
(a) Mercury(II) chloride
(b) Nickel(II) sulphate
(c) Tin(IV) oxide
(d) Thallium(I) sulphate
(e) Iron(III) sulphate
(f) Chromium(III) oxide

While sulphur dioxide and hydrogen peroxide can act as oxidising as well as reducing agents in their reactions, ozone and nitric acid act only as oxidants. Why?

Identify the substance oxidised, reduced, oxidising agent and reducing agent for each of the following reactions:

(a) 2AgBr _(s) + C₆H₆O_2(aq) → 2Ag_(s) + 2HBr _(aq) + C₆H₄O_2(aq)

(b) HCHO_(l) + 2[Ag (NH₃)₂]⁺_(aq) + 3OH^-_(aq) → 2Ag_(s) + HCOO^-_(aq) + 4NH_3(aq) + 2H₂O_(l)

(c) HCHO _(l) + 2Cu²⁺_(aq) + 5 OH^-_(aq) → Cu₂O_(s) + HCOO^-_(aq) + 3H₂O_(l)

(d) N₂H_4(l) + 2H₂O_2(l) → N_2(g) + 4H₂O_(l)

(e) Pb_(s) + PbO_2(s) + 2H₂SO_4(aq) → 2PbSO_4(s) + 2H₂O_(l)

The compound AgF₂ is an unstable compound. However, if formed, the compound acts as a very strong oxidizing agent. Why?

How do you account for the formation of ethane during chlorination of methane?

What are hybridisation states of each carbon atom in the following compounds ?

(i) CH₂=C=O,

(ii) CH₃CH=CH₂,

(iii) (CH₃)₂CO,

(iv) CH₂=CHCN,

(v) C₆H₆

What will be the minimum pressure required to compress 500 dm³ of air at 1 bar to 200 dm³ at 30°C?

What are the common physical and chemical features of alkali metals?

Calculate the molecular mass of the following:
(i) H₂O
(ii) CO₂
(iii) CH₄

What is the basic theme of organisation in the periodic table?

Explain the formation of a chemical bond.

Choose the correct answer. A thermodynamic state function is a quantity
(i) used to determine heat changes
(ii) whose value is independent of path
(iii) used to determine pressure volume work
(iv) whose value depends on temperature only.

A liquid is in equilibrium with its vapour in a sealed container at a fixed temperature. The volume of the container is suddenly increased.
a) What is the initial effect of the change on vapour pressure?
b) How do rates of evaporation and condensation change initially?
c) What happens when equilibrium is restored finally and what will be the final vapour pressure?

Justify the position of hydrogen in the periodic table on the basis of its electronic configuration.

Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation.

(a) C₆H₅OH

(b) C₆H₅NO₂

(c) CH₃CH=CHCHO

(d) C₆H₅–CHO

(e) C₆ H₅ - C⁺H₂ 

(f)  CH₃CH = CHC⁺H₂

How will you convert benzene into

(i) p - nitrobromobenzene

(ii) m - nitrochlorobenzene

(iii) p - nitrotoluene

(iv) acetophenone?

In a process, 701 J of heat is absorbed by a system and 394 J ofwork is done by the system. What is the change in internal energy for the process?

Identify the functional groups in the following compounds

The enthalpy of combustion of methane, graphite and dihydrogen at 298 K are, –890.3 kJ mol^–1  , –393.5 kJ mol^–1, and –285.8 kJ mol^–1 respectively. Enthalpy of formation of CH₄(g) will be

(i) –74.8 kJ mol^–1

(ii) –52.27 kJ mol^–1

(iii) +74.8 kJ mol^–1

(iv) +52.26 kJ mol^–1

Which of the alkali metal is having least melting point?

(a) Na (b) K (c) Rb (d) Cs

What is meant by the conjugate acid-base pair? Find the conjugate acid/base for the following species:

HNO₂,  CN^– ,  HClO₄,  F ^–,  OH^–,  CO^2–₃  and  S^-

Electrons are emitted with zero velocity from a metal surface when it is exposed to radiation of wavelength 6800 Å. Calculate threshold frequency (v₀) and work function (W₀) of the metal.

Explain what happens when boric acid is heated.

The ionization constant of dimethylamine is 5.4 x 10^-4. Calculate its degree of ionization in its 0.02 M solution. What percentage of dimethylamine is ionized if the solution is also 0.1 M in NaOH?