III Group EXPLAIN WITH REASON 1. Although aluminium is above hydrogen in the electrochemical series, it is stable in air and water

2. In the electrolytic manufacture of aluminium carbon anodes are consumed.

3. Cryolite is added to alumina in the electrolytic manufacture of aluminium

4. Anhydrous AlCl3 fumes in air

5. Alum is used in setting muddy water

6. It is necessary to purify bauxite ore before it is subjected to electrolytic reduction.

7. Boron tribromide is stronger acid than boron trifluoride

8. Boron and aluminium halides behave as Lewis acids

9. Pure alumina cannot be electrolysed

10. Aqueous AlCl3 solution behaves acidic towards litmus while that of NaCl does not

11. Aluminium forms [AlF6]3- ion but boron does not form [BF6]3-

12. AlF3 is a high melting solid while AlCl3 is a low melting volatile solid

13. Aluminium becomes passive in concentrated nitric acid

14. Aluminium chloride forms a dimer while boron trichloride does not form a dimer.

15. Aluminium metal is frequently used as reducing agent in the extraction of chromium and manganese

16. Aluminium generally forms covalent compounds

17. Anhydrous aluminium choride cannot be prepared by heating hydrated AlCl36H2O

18. Aluminium vessels should not be cleaned with cleaning agent containing washing soda

19. Duralumin is used in aircraft industry

20. The hydroxides of aluminium and iron are insoluble in water however NaOH is used to separate one from the other.

21. Boron has high m.pt and b.pt

22. Boron does not form B3+ ion

23. Aluminium cannot be prepared by the electrolysis of aqueous solution of its salt

24. Fine aluminium powder when exposed to air becomes hazardous.

25. B(OH)3 is an acid, Al(OH)3 is amphoteric and Tl(OH)3 is basic

26. Boron never forms compounds in unipositive state but Thallium is quite stable in unipositive state

27. The pp - pp back bonding occurs in the halides of boron but not in the halides of aluminium.

28. Molten AlBr3 is a poor conductor but aqueous AlBr3 is a good conductor of electricity

29. The B-X bond distance is shorter than the sum of the covalent radii of boron and halogen (X)

30. Certain metallic oxides are reduced with aluminium rather than with carbon.

31. Boric acid can be titrated against sodium hydroxide using methyl orange as indicator only in the presence of polyhydroxy compounds like catechol

32. Aluminium sulphide gives foul odour when it becomes damp. Write balanced chemical equation for the reaction.

33. Arrange the following ions in order of their increasing radii Li+, Mg2+, K+, Al3+

Starting from boric acid how would you prepare.

(1) Boric anhydride (2) Boron trichloride (3) Boron trifluoride (4) Boron hydrides (5) Ethyl borate (6) Meta and tetra boric acids

How will you obtain 1) Anhydrous aluminium chloride from aluminium

2) Anhydrous aluminium chloride from alumina

3) Potash alum from aluminium sulphate

4) Anhydrous aluminium chloride from potash alum

5) Borax from colemanite

6) Boric acid from borax and colemanite

7) Boron from boric acid

8) Aluminium chloride from aluminium sulphate

9) Aluminium sulphate from potash alum.

What happens when 1) Excess of caustic soda is added to a solution of aluminium chloride

2) Dry chlorine gas is passed over hot mixture of aluminium and coke

3) Water is added to aluminium nitride

4) Borax is heated strongly

5) Sodium hydroxide is added to potash alum

6) Ammonium hydroxide is added to potash alum

7) Potash alum is heated strongly

8) Anhydrous aluminium is heated strongly

9) Boric acid is heated

10) Hydrated aluminium chloride is heated

11) Alumina is heated in a stream of sulphur monochloride vapour and chlorine

12) Aluminium is heated with hot concentrated sodium hydroxide

13) Aluminium is heated with carbon and the product is hydrolysed

14) Aluminium is heated with nitrogen and the product is hydrolysed

15) Aluminium is treated with dilute nitric acid.

16) A mixture of aluminium fillings and iron oxide is ignited

State whether the following statements true or false 1) Aluminium is ionic in all of its compounds

2) Aluminium is the third most abundant metal on earth

3) All the Al-Cl bonds in Al2Cl6 are equivalent

4) Potash alum is water soluble and ionizes in aqueous solution to give three types of ions

5) The basic nature of the hydroxides of group B(IIIA) decrease progressively down the group

6) Thermite is a mixture of alumina and iron

7) Ultramarine is an artificial blue pigment

8) Aluminium hydroxide is soluble in ammonium hydroxide

9) Gold Schmidt thermite process is used in the extraction of aluminium

10) Al2O3 can be converted to Al by passing H2 over it

11) Borax when heated with ammonium chloride forms ammonium ………..

12) Boron dissolves in hydrochloric acid

13) Al2O3 is water soluble and gives Al(OH)3

14) H3BO3 is monobasic acid

15) Boron halides possess resonance structure.

16) Many gems contain Al2O3.

17) The maximum covalency of aluminium is 4

18) TlOH is a strong base

19) Jeweller’s Borax is Na2B4O7 5H2O

Give the formula of the following:

1) Panderinite 2) Corundum 3) Rajorite 4) Alunite 5) Jeweller’s Borax

6) Turquoise 7) Felspar 8) Colemanite 9) Cryolite 10) Mica

Arrange the following in the order asked against each:

1) BCl3, AlCl3, GaCl3 increasing ionic character.

2) BF3, BCl3, BBr3 increasing Lewis acid character.

3) BCl3, AlCl3, GaCl3, InCl3 increasing Lewis acid character.

4) Li2O, BeO, B2O3, CO2 increasing basic character.

5) B2O3, Al2O3, Be2O3, In2O3 increasing acidic character.

6) LiCl, BeCl2, MgCl2, AlCl3. Decreasing pH of the aqueous solution.

PROBLEMS 1. Identify A and B in the following reactions

Colemanite + A ® Na2B4O7

Na2B4O7 + B ® H3BO3

2. An inorganic Lewis acid X shows the following reactions.

(i) It fumes in moist air

(ii) the intensity of fumes increases when a rod dipped in NH4OH is brought near to it

(iii) An acidic solution of X on adding NH4Cl and NH4OH gives a precipitate which dissolves in NaOH

solution

(iv) An acidic solution of X does not give a precipitate with H2S

Identify X and give chemical reactions in steps i to iii

3. An inorganic compound A shows the following reactions

(i) It is a white solid exists as dimer and fumes in wet air

(ii) it sublimes at 180oC and forms mononer if heated to 400oC

(iii) it aqueous solution turns blue litmus to red and gives a white precipitate with AgNO3 solution which

is soluble in NH4OH

(iv) Addition of NH4OH and NaOH separately to the solution of A gives a gelatinous precipitate which

is, however soluble in excess of NaOH

Identify the compound

4. A certain salt X gives the following tests.

(i) Its aqueous solution is alkaline to litmus

(ii) On strongly heating it swells to give a glassy material

(iii) When concentrated sulphuric aicd is added to a hot concentrated solution of X white crystals of weak acid separates out. Identify X and write down the chemical equations for reactions at steps (i) (ii) and (iii)

5. The metallic salt XY is soluble in water

When the solution is treated with NaOH solution, a white precipitate A is formed. This precipitate is soluble in excess of NaOH solution to form a compound B. When this solution is boiled with solid NH4Cl, a precipitate of a compound C is formed. An aqueous solution of XY upon treatment with BaCl2 solution gave a white precipitate D which was insoluble indilute HCl. The salt XY forms a double salt with potassium sulphate.

Identify XY and give equations for reactions

6. (i) A white precipitate B is formed when a mineral A is boiled with Na2CO3 solution.

(ii) The precipitate is filtered and the filtrate contain two compounds C and D. The compound C is removed by crystallization and when CO2 is passed through the mother liquor left D changes to C

(iii) The compound C on strong heating gives two compounds D and E

(iv) E on heating with cobalt oxide produces blue coloured substance F

Identify A to F and give chemical reactions for the reactions at the steps i to iv

7. A white crystalline compound A swells up on heating and gives violet coloured flame on Bunsen flame. Its aqueous solution gives the following reactions

a) A white precipitate with BaCl2 in presence of HCl b) When treated with excess of NH4OH, it gives white gelatinous precipitate. The white

precipitate dissolves in NaOH and reappears on boiling with concentrated solution of NH4Cl c) It gives yellow precipitate with cobaltinitrite solution identify the compound (A) and explain

the reactions.