Group VI Assignment
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Assignment given by Dr. Manisha Jain
B.Sc(H) Chem/II -NS Paper - VII (Group-VI) Q.1. Justify the following statements: 1. CO2 is a stable gas, CS2 is comparatively unstable, CSe2 exists as a polymer whereas CTe2 is not known. 2. Action of conc. HNO3 on elemental sulphur generates sulphuric acid while with selenium, selenious acid is the final product. 3. A large number of condensed silicates, many polyphosphates and a few polysulphates are known but no polychlorate is known. 4. TeF6 is rapidly hydrolysed to telluric acid while SF6 is not attacked even by boiling alkali. 5. The compounds with S-S bonds are more numerous and stable than those of O-O, Se -Se and Te -Te bonds. 6. The process of addition of an electron to oxygen atom is exothermic whereas it is endothermic for nitrogen. 7. The process of addition of electrons to Oxygen ( O + 2 e- O2-) is endothermic (note the difference between 6 and 7) still a large number of compounds containing this ion exists. 8. Unlike SO2, SeO2 is a solid with chain structure. 9. An aqueous solution of SO2 is a stronger reducing agent in alkaline medium than in acidic medium. 10. Sulphuric acid is formulated as H2SO4 while telluric acid as Te(OH)6. 11. Oxygen is colourless in gaseous state but aquires pale blue colour in solid state. 12. NO+ has a shorter bond length than NO even though the later has an extra electron. 13. Liquid oxygen sticks to the poles of the magnet while liquid dinitrogen does not. 14. Oxygen exists as O2 while sulphur exists as S8. 15. SOCl2 can act both as a lewis acid and a lewis base. 16. S-O bond strength in oxyhalides of sulphur follow the order SOBr2 < SOCl2 < SOF217. H2O is a liquid but H2S is a gas. 18. Of all hexahalides, only hexafluorides are known for group VI elements. 19. Selenic acid is a weaker acid but a stronger oxidizing agent than sulphuric acid. 20. When a sulphite solution is boiled with labelled S35, labelled thiosulphate is obtained. This on acidification gives a solution which is not radioactive and a radioctive yellow ppt. 21. Thiosulphuric acid can't be prepared by acidification of thiosulphates. 22. Extent of autoionisation in sulphuric acid is much higher than that in water, still unlike water, sulphuric acid is not used as a common solvent. 23. Sulphurous acid and sulphites are reducing in nature. Q.2. Predict giving reasons: 1. Which is paramagnetic O22- or O2- 2. Stronger oxidising agent H2SO4 or H2SeO4 3. Longer O-F bond O2F2 or OF2 4. Not known SF6 or OF6 Q.3. Do you agree with the following statements? Justify your answer. 1. The lack of reactivity of SF6 is thermodynamic than kinetic in nature 2. Among the oxoacids of an element, the acidic strength increases with increase in the number of oxygen atoms present in the molecule. 3. Pattern of stability of tetrahalides illustrates the interplay of oxidising power of the halogen and the resistance of group VI elements towards oxidation. Q.4. a. Compare the boiling points and acid strengths in the series where H2X where X is O,S, Se, Te. Explain the trends. b. Describe the changes which occur on heating sulphur. c. Describe one method by which H2O2 is prepared. Give the structure of H2O2 in gas phase. Write balanced equations for the reaction of H2O2 with(i) an acidified solution of potassium permanganate (ii) aqueous HI (iii) an acidic solution of potassium hexacyanoferrate. d. What are thionic acids? Give their structural relations. How are polythionates prepared?
a. O3 + KOH b. SCl2 + SO32- H2SO4 c. H2NCONH2 + SO3 d. SF4 + I2O5 e. KIO4 + H2O2 f. Na2S2O3 + I2 g. NaHSO3 h. SOCl2 + H2O
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