Chemistry

Lithium resembles magnesium in some of its properties. Mention two such properties and give reasons for this resemblance.

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These two elements have similar properties because of their similar atomic and ionic radii.

(i) Both are lighter element and harder than the other metals in their respective groups.

(ii) The halides of both elements, LiCl and MgCl₂ are soluble in ethanol.

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58. Match the intermediates given in Column I with their probable structure in Column II.

Column I	Column II
(i) Free radical	(a) Trigonal planar
(ii) Carbocation	(b) Pyramidal
(iii) Carbanion	(c) Linear

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58. (i) → (a); (ii) → (a); (iii) → (b)

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Complete the following reactions

(i) O₂^2– + H₂O →

(ii) O₂^– + H₂O →

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(i) O₂²⁻+ 2H₂O → H₂O₂+2OH⁻

(ii) 2O₂⁻+2H₂O→2OH⁻+H₂O₂+O₂

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Match Column I with Column II.

Column I	Column II
(i) Dumas method	(a) AgNO3
(ii) Kjeldahl's method	(b) Silica gel
(iii) Carius method	(c) Nitrogen gas
(iv) Chromatography	(d) Free radicals
(v) Hemolysis	(e) Ammonium sulphate

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57. Match the terms mentioned in Column I with the terms in Column II.

Column I	Column II
(i) Carbocation	(a) Cyclohexane and 1- hexane
(ii) Nucleophile	(b) Conjugation of electrons of C–H bond with empty p-orbital present at adjacent positively charged carbon.
(iii) Hyperconjugation	(c) sp²hybridized carbon with empty p-orbital
(iv) Isomers	(d) Ethyne
(v) sp hybridization	(e) Species that can receive a pair of electrons
(vi) Electrophile	(f) Species that can supply a pair of electrons

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57. (i) → (c); (ii) → (f); (iii) → (b) : (iv) → (a); (v) → (d) ; (vi) → (e)

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When heated in air, the alkali metals form various oxides. Mention the oxides formed by Li, Na and K

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Alkali metals forms oxide when reacted with air. Lithium forms monoxide, sodium forms peroxide and potassium forms superoxide.

4Li+O₂→2Li₂O

Na+O₂→Na₂O₂

K+O₂→KO₂

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How do you account for the strong reducing power of lithium in aqueous solution?

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Lithium has the highest negative reduction potential value. Due to the small size of lithium it has the highest ionization enthalpy. Due to this, the reducing power of lithium is the highest in an aqueous solution.

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56. Match the type of mixture of compounds in Column I with the technique of separation/purification given in Column II.

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56. (i) → (e); (ii) → (d); (iii) → (a) : (iv) → (b); (v) → (c)

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55. Hyperconjugation involves delocalization of ______.

(i) Electrons of carbon-hydrogen σ bond of an alkyl group directly attached to an atom of unsaturated system.

(ii) Electrons of carbon-hydrogen σ bond of alkyl group directly attached to the positively charged carbon atom.

(iii) π-electrons of carbon-carbon bond

(iv) One pair of electrons

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55. Options (i) and (ii) are correct since hyperconjugation involves the delocalization of electrons of C—H bond of an alkyl group directly attached to an atom of unsaturated system or to an atom with an unshared p-orbital. The electrons of C—H bond of the alkyl group enter into partial conjugation with the attached unsaturated system or with the unshared p-orbital. This is a permanent effect. Hyperconjugation can be shown as-

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Ions of an element of group 1 participate in the transmission of nerve signals and transport of sugars and amino acids into cells. This element imparts yellow colouctor the flame in flame test and forms an oxide and a peroxide with oxygen. Identify the element and write a chemical reaction to show the formation of its peroxide. Why does the element impart colour to the flame?

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