Class 11th

5.32. Which of the following gases will have the lowest rate of diffusion?

(a) H₂

(b) N₂

(c) F₂

(d) O₂

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5.32. (c) F₂

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5.31. Viscosity of a liquid is a measure of

(a) Repulsive forces between the liquid molecules

(b) Frictional resistance

(c) Intermolecular forces between the molecules

(d) None of the above

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5.31. (b) frictional resistance

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5.30. With rise in temperature, the surface tension of a liquid

(a) Decreases

(b) Increases

(c) Remaining the same

(d) None of the above

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5.30. (a) decreases

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8.23. Chlorine is used to purify drinking water. Excess of chlorine is harmful. The excess of chlorine is removed by treating with sulphur dioxide. Present a balanced equation for this redox change taking place in water.

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The balanced chemical reaction for the redox reaction between chlorine and sulphur dioxide is:

Cl₂? + SO₂? + 2H₂? O → 2Cl⁻ + SO₄²⁻? + 4H⁺.

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8.22. Consider the elements:

Cs, Ne, I, F
(a) Identify the element that exhibits negative oxidation state.
(b) Identify the element that exhibits positive oxidation state.
(c) Identify the element that exhibits both positive and negative oxidation states.
(d) Identify the element which neither exhibits negative nor does the positive oxidation state.

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(a) F. Fluorine being the most electronegative element shows only a -ve oxidation state of -1.

(b) Cs. Alkali metals because of the presence of a single electron in the valence shell, exhibit an oxidation state of +1.

(c) I. Because of the presence of seven electrons in the valence shell, I shows an oxidation state of -1 (in compounds of I with more electropositive elements such as H, Na, K, Ca, etc.) or an oxidation state of +1 compounds of I with more electronegative elements, i.e., O, F, etc.) and because of the presence of d-orbitals it also exhibits +ve oxidation states of +3, +5 and +7.

(d) Ne. It is an inert gas (with high ioni

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5.29. At constant temperature, the pressure of the gas is reduced to one-third, the volume

(a) Reduce to one-third

(b) Increases by three times

(c) Remaining the same

(d) Cannot be predicted

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5.29. (b) increases by three times

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8.21. The Mn³⁺ion is unstable in solution and undergoes disproportionation to give Mn²⁺, MnO₂ and H⁺ ion. Write a balanced ionic equation for the reaction.

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The unbalanced chemical reaction is:
Mn³⁺ (aq) → Mn²⁺ (aq) + MnO₂? (s) + H⁺ (aq)
The oxidation half reaction is,
Mn³⁺ (aq) → MnO₂? (s).
To balance oxidation number, one electron is added on R.H.S.
Mn³⁺ (aq) → MnO₂? (s) + e⁻
4 protons are added to balance the charge.
Mn³⁺ (aq) → MnO₂? (s) + 4H⁺ (aq) + e⁻
2 water molecules are added to balance O atoms.
The reduction half reaction is Mn³⁺ (aq) → Mn²⁺ (aq).
An electron is added to balance oxidation number.
Mn³⁺ (aq) + e⁻ → Mn²⁺ (aq)
Two half-cell reactions are added to obtain balanced chemical equation.
2Mn³⁺ (aq) + 2H₂? O (l) → Mn2+ (aq) + MnO₂? (s) + 4H⁺ (aq)

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MCQs:

5.28. The average kinetic energy of the gas molecule is

(a) Inversely proportional to its absolute temperature

(b) Directly proportional to its absolute temperature

(c) Equal to the square of its absolute temperature

(d) All of the above

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5.28. (b) directly proportional to its absolute temperature

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8.20. What sorts of information can you draw from the following reaction?
(CN)₂(g) + 2OH^–(aq) → CN^–(aq) + CNO^–(aq) + H₂O(l)

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Let x be the O.N. of C.
O.N. of C in cyanogen, (CN)₂ = 2 (x – 3) = 0 or x = +3

O.N. of C in cyanide ion, CN^- = x – 3 = -1 or x = +2

O.N. of C in cyanate ion, CNO =x-3-2 = -l or x: = +4

The four information about the reaction are:
(i) The reaction involves decomposition of cyanogen, (CN)₂ in the alkaline medium to cyanide ion, CN and cyanate ion, CNO^–.

(ii) The O.N. of C decreases from +3 in (CN)₂ to +2 in CN^–ion and increases from +3 in (CN)₂ to +4 in CNO^– ion. Thus, cyanogen is simultaneously reduced to cyanide ion and oxidised to cyanate ion.

(iii) It is an example of a redox reaction in general an

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5.27. Assertion: At high altitudes, liquids boil at lower temperatures in comparison to that at sea level.

Reason: At high altitudes atmospheric pressure is high.

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