InterviewSolution
Saved Bookmarks
InterviewSolution
| 1. |
On heating the viscosity of liquid sulphur areA. incrasesB. decreasesC. first increasea and then decreasesD. first decrease and the n increase |
|
Answer» Correct Answer - 2 Both rhombic and monoclinic sulphur melt to forms a low-visosity straw-colord liquid. Owing to the conversion of rhomble to monocline sulphure,and also to possible variations in the percentage ofa llotropes of liquid sulphur formed,the melting points are not sharp, rhombic sulphur melts at approxmately `113^(@)C` whist monoclinic sulphur at approximately `119^(@)C`. But when the liquid is heated, there is an abrupt change in propertics at `159^(@)C`. The most dramatic transformation is a `10^(4)`-fold increases in visosity.The liquid also darkness considerably until it is nearly black and becomes viscous. We can explain these change in terms of a rupture of the `S_(8)` rings . The octasulphur chain then link one to another to form polymers containing as many as `20,000 S` atoms. Thus, the rise in viscocity is explained by a replacement of the free-moving `S_(8)` molecules by these interwined chains, which have strong dispersion force interactions. The viscosity increases sharply abd continue to rise up to`200^(@)C`. At about `200^(@)C` the viscosity begins to fall and at its boiling point of `445^(@)C` the liquids is again mobile. When sulphur vapour come in contact with a cool surface it sublimes to give a pale yellow solid. The drcreases in viscosity of liquid sulphur that occurs above `200^(@)C` is explained as being due to the breakdown of these long chains and the reforming fo `S_(8)` rinds. Sulphur vapour contains `S_(8)` rings ,together with small fragments such as `S_(6),S_(4)` consist of `S_(2)` molecules. At `600^(@)C` the gas mainly consists of `S_(2)` molecules. At very high temperatures,atomic sulphur is formed. The `S_(2)` molecules is paramagnetic and blue colored like `O_(2)` and prsumably has similarly bonding. `S_(2)` gas is stable up to `2200^(@)C` .The stability of `S_(2)` is used in the quantitative analysis of `S` compounds. They are burnt in a reducing flame, and the color from excited `S_(2)` is measured spactrophotometrically .`S_(3)` and `S_(4)` are also known . |
|