SOME pBLOCK ELEMENTS 26 Classify the following oxides

SOME p-BLOCK ELEMENTS

26. Classify the following oxides as neutral, acidic, basic, & amphoteric. Tl 2 O 3, CO, B 2 O 3, Si. O 2, CO 2, Al 2 O 3 Ans: Neutral: - CO Acidic: - B 2 O 3, Si. O 2, CO 2 Amphoteric: - Al 2 O 3 Basic: - Tl 2 O 3

27. In some of reactions, thallium resembles aluminium, whereas in some others it resembles with group I metals. Support this statement by giving some evidences. Ans: Aluminium shows a uniform oxidation of +3. Like aluminium, Tl also shows oxidation state of +3 in some of its compounds like Ti. Cl 3, Tl 2 O 3, etc. like Al, Tl also forms octahedral complexes : [Al. F 6]3 - and [Tif 6]3 -. Group 1 metals shows a oxidation state of +1. Like group 1 metals, Tl due to inert pair effect also shows +1 oxidation state in some of its compounds like Tl 2 O, Tl. Cl. O 4, etc.

28. When metal X is treated with Naoh a white ppt. (A) is obtained, which is soluble in excess of Na. OH to give a soluble complex (B). compound (A) is soluble in dil. HCl to form compound (C). the compound (A) when heated strongly give (D), which is used to extract metals. Indentify all the compounds. Ans: Since metal (X) reacts with Na. OH to first give white ppt. (A) which dissolves in excess of Na. OH to give soluble complex (B), therefore metal (X) must be Al; ppt (A) must be Al(OH)3 and complex (B) must be Na+[Al(OH)4]2 Al + 3 Na. OH Al(OH)3 + 3 Na+ Al(OH)3 + Na. OH Na+[Al(OH)4]Since (A) is amphoteric in nature, it reacts give dil. HCl to form (C) must be Al. Cl 3 Al(OH)3 + 3 HCl Al. Cl 3 + 3 H 2 O Since (A) on heating given (D) which is used to extract metal, therefore (D) must be Al 2 O 3 2 Al(OH)3 Al 2 O 3 + 3 H 2 O

29. What do you understand by the following: Ans: Inert pair effect: - as we move down the group the tendency of s-electrons to participate in bond formation decreases. This effect is known as inert pair effect. Allotropy: -the phenomenon of existence of elements in two or more forms which have different physical properties but same chemical properties is called allotropy. Catenation: -ability of like atoms to link one another through covalent bonds.

30. A certain salt X, gives the fol. Results: (i) its aq. Is alkaline to litmus (ii) it swells up to glassy material Y on strong heating (iii) when conc. H 2 SO 4 is added to hot solution of X, white crystal of acid Z separates out. Write eqns. For all above reactions and identify X, Y, Z. Ans: Na 2 B 4 O 7. 10 H 2 O 2 Na. OH + H 2 B 4 O 7 + 8 H 2 O Na 2 B 4 O 7. 10 H 2 O Na 2 B 4 O 7 + 10 H 2 O Na 2 B 4 O 7 2 Na. BO 2 + B 2 O 3 Na 2 B 4 O 7. 10 H 2 O + H 2 SO 4 4 H 3 BO 3 + Na 2 SO 4 + 5 H 2 O

31 write the balanced equations for: (i) BF 3 + Li. H (ii) B 2 H 6 + H 2 O (iii) Na. H + B 2 H 6 (iv) H 3 BO 3 (v) Al + Na. OH (vi) B 2 H 6 + NH 3 Ans: 2 BF 3 +6 Li. H B 2 H 6 + 6 Li. F B 2 H 6 + 6 H 2 O 2 H 3 BO 3 + 6 H 2 2 Na. H + B 2 H 6 2 Na+[NH 4]H 3 BO 3 HBO 2 + H 2 O 2 Al + 2 Na. OH 2 Na+[Al(OH)4]- + 3 H 2 B 2 H 6 +2 NH 3 2 BH 3. NH 3

32. Give one method for industrial and laboratory preparation of CO and CO 2 each. Ans: Industrial : 2 C + O 2 2 CO; C + O 2 CO 2 Laboratory: HCOOH CO + H 2 O; Ca. CO 3 + 2 HCl Ca. Cl 2 + CO 2 + H 2 O 33. An aq. Sol. Of Borax is: (a) neutral (b)amphoteric (c) basic (d) acidic Ans: - (c)

34. Boric acid is polymeric due to : (a) its acidic nature (b)the presence of hydrogen bonds (c) its monobasic nature (d) its geometry Ans: - (b) 35. The type of hybridization of boron in diborane is (a) sp (b) sp 2 (c) sp 3 (d)dsp 2 Ans: - (c)

36. Thermodynamically the most stable form of carbon is: (a) diamond (b) graphite (c) fullerenes (d)coal Ans: - (b) 37. Elements group 14. (a)exhibits oxidation state of +4 only (b) exhibit oxidation state of +2 and +4 (c) forms M 2 - and M 4 - ion (d) form M 2+ and M 4+ ions Ans: - (b)

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