Class 11th

5.24. Assertion: Viscosity of liquids decreases as the temperature rises.

Reason: Molecules of liquids are held together by attractive intermolecular forces.

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5.24. (b) Viscosity of liquids decreases as the temperature rises because at high temperature molecules have high kinetic energy and can overcome the intermolecular forces to slip past one another between the layers.

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Assertion and Reason:

Directions:

(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.

(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.

(c) Assertion is correct statement but reason is wrong statement.

(d) Assertion is wrong statement but reason is correct statement.

5.23. Assertion: The dipole-dipole interactionbetween two HCl moleculesis stronger than the London forces.

Reason: Only partial charges are involved

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5.23. (a) The dipole-dipole interaction between two HCl molecules is stronger than the London forces but is weaker than ion-ion interaction because only partial charges are involved.

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8.17. Consider the reactions:
(a) H₃PO₂(aq) + 4AgNO₃(aq) + 2H₂O(l) → H₃PO₄(aq) + 4Ag(s) + 4HNO₃(aq)
(b) H₃PO₂(aq) + 2CuSO₄(aq) + 2H₂O(l) → H₃PO₄(aq) + 2Cu(s) + H₂SO₄(aq)
(c) C₆H₅CHO(l) + 2[Ag(NH₃)₂]⁺(aq) + 3OH^–(aq→ C₆H₅COO^–(aq) + 2Ag(s) + 4NH₃(aq) + 2H₂O(l)
(d) C₆H₅CHO(l) + 2Cu²⁺(aq) + 5OH^–(aq) → No change observed
What inference do you draw about the behaviour of Ag⁺and Cu²⁺ from these reactions?

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Reactions (a) and (b) indicate that H₃PO₂ (hypophosphorous acid) is a reducing agent and thus reduces both AgNO₃ and CuSO₄ to Ag and Cu respectively. Conversely, both AgNO₃ and CuSO₄ act as oxidising agent and thus oxidise H₃PO₂to H₃PO₄ (orthophosphoric acid) Reaction (c) suggests that [Ag (NH₃)₂]⁺ oxidises C₆H₅CHO (benzaldehyde) to C₆H₅COO^– (benzoate ion) but reaction (d) indicates that Cu²⁺ ions cannot oxidise C₆H₅CHO to C₆H₅COO^–. Therefore, from the above reactions, we conclude that Ag⁺ ion is a strong deoxidising agent than Cu²⁺ ion.

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8.16. Why does the following reaction occur?

XeO₆^4– (aq) + 2F^– (aq) + 6H⁺(aq) → XeO₃(g)+ F₂(g) + 3H₂O(l)

What conclusion about the compound Na₄XeO₆ (of which XeO₆^4– is a part) can be drawn from the reaction?

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XeO₆⁴⁻? oxidizes F⁻ and F⁻ reduces XeO₆⁴⁻?
Hence, the given reaction occurs.
The oxidation number of Xe decreases from +8 to +6. The oxidation number of F increases from -1 to 0.
Thus, Na₄? XeO₆? is a stronger oxidising agent than F⁻.

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8.15. Justify giving reactions that among halogens, fluorine is the best oxidant and among hydrohalic compounds, hydroiodic acid is the best reductant.

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Fluorine oxidizes chloride ion to chlorine, bromide ion to bromine and iodide ion to iodine respectively.
F₂? + 2Cl⁻ → 2F⁻ + Cl₂?
F₂? + 2Br⁻ → 2F⁻ + Br₂?
F_2? + 2I⁻ → 2F⁻ + I₂?

Chlorine oxidizes bromide ion to bromine and iodide ion to iodine.
Cl_2? + Br⁻ → 2Cl⁻ + Br₂?
Cl₂? + I⁻ → 2Cl⁻ + I₂?

Bromine oxidizes iodide ion to iodine.
Br₂? + I⁻ → 2Br⁻ + I₂?

But bromine and chlorine cannot oxidize fluoride to fluorine. Hence, fluorine is the best oxidizing agent amongst the halogens. The decreasing order of the oxidizing power of halogens is F₂? >Cl₂? >Br₂? >I₂?

HI and HBr can reduce sulphuric acid

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Why does the same reductant, thiosulphate react differently with iodine and bromine?

8.14. Consider the reactions:

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The average O.N. of S in S₂O₃^2- is +2 while in S₄O₆^2- it is + 2.5. The O.N. of S in SO₄^2- is +6. Since Br₂ is a stronger oxidising agent than I₂, it oxidises S of S₂O₃^2- to a higher oxidation state of +6 and hence forms SO₄^2- ion. I₂, however, being weaker oxidising agent oxidises S of S₂O₃^2- ion to a lower oxidation of +2.5 in S₄O₆^2- ion. It is because of this reason that thiosulphate reacts differently with Br₂ and I₂.

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

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Substance oxidised	Substance reduced	Oxidising agent	Reducing agent
(a) C₆H₁₂O₆	AgBr	C₆H₁₂O₆
(b) HCHO	[Ag (NH₃)₂]⁺	[Ag (NH₃)₂]⁺	HCHO
(c) HCHO	Cu²⁺	HCHO
(d) N₂H₄	H₂O₂	N₂H₄
(e) Pb	PbO₂	Pb

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5.22. Critical temperature for CO₂ and CH₄ are 31.1°C and -81.9°C respectively. Which of these has stronger intermolecular forces and why?

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5.22. Higher the critical temperature, more easily the gas can be liquefied, i.e., greater are the intermolecular forces of attraction. Hence, CO₂ has stronger intermolecular forces than CH₄.

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8.12. How do you account for the following observations?
(a) Though alkaline potassium permanganate and acidic potassium permanganate both are used as oxidants, yet in the manufacture of benzoic acid from toluene we use alcoholic potassium permanganate as an oxidant. Why? Write a balanced redox equation for the reaction.

(b) When concentrated sulphuric acid is added to an inorganic mixture containing chloride, we get colourless pungent smelling gas HCl, but if the mixture contains bromide then we get red vapour of bromine. Why?

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(a) Toluene can be oxidised to benzoic acid in acidic, basic and neutral media according to the following redox equations:

In the laboratory, benzoic acid is usually prepared by alcoholic KMnO₄ oxidation of toluene. However, in industry alcoholic KMnO₄ is preferred over acidic or alkaline KMnO₄ because of the following reasons:
(i) The cost of adding an acid or the base is avoided because in the neutral medium, the base (OH^- ions) are produced in the reaction itself.
(ii) Since reactions occur faster in homogeneous medium than in heterogeneous medium, therefore, alcohol helps in mixing the two reactants, i.e., KMnO₄

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5.21. In terms of Charles' law explain why -273°C is the lowest possible temperature.

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