Group III Assignment

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Assignment given by Dr. Manisha Jain
          B.Sc(H) Chem/II -NS
               Paper - VII
                                                                Marks: 25

Q.1. Provide a suitable explanation for the following:

1. First ionization energy of Group III elements follow an irregular trend B > Al < Ga > In < Tl

2. Boric acid behaves as a weak monobasic acid but behaves as a strong acid in the presence of glycol.

3. TlIIII3 is unstable relative to TlII3 whereas opposite is true for Al, Ga and In.

4. Structurally boron nitride is similar to graphite; however it is not an electrical conductor.

5. AlF3 is almost insoluble in anhydrous HF, but dissolves if KF is also present. Passage of BF3 through the same solution results in reprecipitation of AlF3.

6. BI3 does not form addition compound with ammonia while BF3 does it easily.

7. The rate of exchange of water is much faster in [Al(H2O)6]3+ than in [Cr(H2O)6]3+Superscript text .

8. The rate of hydrolysis of diborane by water vapour is proportional to P1/2 B2H6. P1/2 H2O.

9. 2,6-Dimethylpyridine, although a stronger base towards proton than pyridine, differs from the later by not forming an adduct with boron trimethyl; it does however combine with aluminium triethyl.

10. LiAlH4 explodes with water whereas NaBH4 does not.

11. The barriers to rotation around the B-N bond in the following aminoboranes display the trend H2B – NR2 > HB-(NR2) > B(-NR2)3

12. Tl+/Tl3+ electrochemical potential sensitive to pH and to the presence of complexing anions.

13. Boron always form covalent compounds.