Chemistry

Chemistry Chemistry NCERT Exemplar Solutions Class 12th Chapter Seven

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This is a short answer type question as classified in NCERT Exemplar

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Write a balanced chemical equation for the reaction showing catalytic oxidation of NH₃ by atmospheric oxygen.

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Chemistry Chemistry NCERT Exemplar Solutions Class 12th Chapter Seven

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This is a short answer type question as classified in NCERT Exemplar

4NH₃ + 5O₂ 4NO + 6H₂O

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In the preparation of H₂SO₄ by Contact Process, why is SO₃ not absorbed directly in water to form H₂SO₄?

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Chemistry Chemistry NCERT Exemplar Solutions Class 12th Chapter Seven

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This is a short answer type question as classified in NCERT Exemplar

SO₃ generates a dense fog of sulphuric acid that does not condense quickly, it is not absorbed directly in water to form H₂SO_4.

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On heating compound (A) gives a gas (B) which is a constituent of air. This gas when treated with 3 mol of hydrogen (H2) in the presence of a catalyst gives another gas (C) which is basic in nature. Gas C on further oxidation in moist condition gives a compound (D) which is a part of acid rain. Identify compounds (A) to (D) also give necessary equations of all the steps involved.

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Chemistry Chemistry NCERT Exemplar Solutions Class 12th Chapter Seven

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This is a long answer type question as classified in NCERT Exemplar

A = NH₄NO₂

B = N₂

C = NH₃

D = HNO₃

(i) NH₄NO₂→N₂ + 2H₂O

(ii) N₂ + 3H₂→2NH₃

(iii) 4NH₃ + 5O₂→4NO + 6H₂O

4NO + O₂→4NO₂

3NO₂ + H₂O→2HNO₃ + NO

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On heating lead (II) nitrate gives a brown gas “A”. The gas “A” on cooling changes to colourless solid “B”. Solid “B” on heating with NO changes to a blue solid 'C'. Identify 'A', 'B' and 'C' and write reactions involved and draw the structures of 'B' and 'C'.

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Chemistry Chemistry NCERT Exemplar Solutions Class 12th Chapter Seven

Contributor-Level 10

This is a long answer type question as classified in NCERT Exemplar

Here, 'A' is NO₂ (Nitrogen dioxide)

'B' is N₂O₄ (dinitrogen tetraoxide)

'C' is N₂O₃ (dinitrogen trioxide)

A brown gas is produced when lead nitrate (II) is heated

2Pb (NO₃)₂ 2PbO + 4NO₂ + O₂

2NO₂ N₂O₄

2NO + N₂O₄ 2N₂O₃

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An amorphous solid “A” burns in air to form a gas “B” which turns lime water milky. The gas is also produced as a by-product during roasting of sulphide ore. This gas decolourises acidified aqueous KMnO₄ solution and reduces Fe₃⁺ to Fe₂⁺ . Identify the solid “A” and the gas “B” and write the reactions involved.

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Contributor-Level 10

This is a long answer type question as classified in NCERT Exemplar

'A' is S₈ 'B' is SO₂ gas

S₈ + 8O₂ 8SO₂

2MnO₄ ^– + 5SO₂ + 2H₂O → 5 SO₄^2– + 4H⁺ + 2Mn²⁺

(violet) (colourless)

2Fe³⁺+ SO₂ + 2H₂O → 2Fe²⁺ + SO₄^2– + 4H⁺

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Assertion (A): A liquid crystallises into a solid and is accompanied by decrease in entropy.

Reason (R): In crystals, molecules organise in an ordered manner.

(i) Both A and R are true and R is the correct explanation of A.

(ii) Both A and R are true but R is not the correct explanation of A.

(iii) A is true but R is false.

(iv) A is false but R is true.

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Contributor-Level 10

This is a Assertion and Reason Type Questions as classified in NCERT Exemplar

option (i)

Explanation: The entropy of a liquid reduces as it crystallises. Because the molecules are more organised in crystalline form.

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Assertion (A): Spontaneous process is an irreversible process and may be reversed by some external agency.

Reason (R): Decrease in enthalpy is a contributory factor for spontaneity.

(i) Both A and R are true and R is the correct explanation of A.

(ii) Both A and R is true but R is not the correct explanation of A.

(iii) A is true but R is false.

(iv) A is false but R is true

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Contributor-Level 10

This is a Assertion and Reason Type Questions as classified in NCERT Exemplar

Ans: (ii)

Explanation: The energy factor for a spontaneous process should be favourable (i.e., -ve) and the randomness should be positive.

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Assertion (A): Combustion of all organic compounds is an exothermic reaction.

Reason (R) : The enthalpies of all elements in their standard state are zero.

(i) Both A and R are true and R is the correct explanation of A.

(ii) Both A and R are true but R is not the correct explanation of A.

(iii) A is true but R is false.

(iv) A is false but R is true.

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Contributor-Level 10

This is a Assertion and Reason Type Questions as classified in NCERT Exemplar

option (ii)

Explanation: The enthalpy of the reactants is always greater than the enthalpy of the product in a combustion reaction.

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Match the following:

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