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Some properties as boiling point, freezing point and vapour pressure of a pure solvent change when solute molecules are added to get homogeneous solution. These are called colligative properties. Applications of colligative properties are useful in day-to day life. Its example is the use of ethylene glycol and water mixture as anti-freezing liquid in the radiator of automobiles. A solution M is prepared by mixing ethanol and water. The mole fraction of ethanol in the mixture is 0.9. Given : Freezing point depression constant of water `(K_(f)^("water"))=1.86" K kg mol"^(-1)` Freezing point depression constant of ethanol `(K_(f)^("ethanol"))=2.0"K kg mol"^(-1)` Boiling point elevation of water `(K_(b)^("water"))=0.52" K kg mol"^(-1)` Boiling point elevation constant of ethanol `(K_(b)^("ethanol"))=1.2" K kg mol"^(-1)` Standard freezing point of water = 273 K Standard freezing point of ethanol = 155.7 K Standard boiling point of water = 373 K Standard boiling point of ethanol = 251.5 K Vapour pressure of pure water = 32.8 mm Hg Vapour pressure of pure ethanol = 40 mm Hg Molecular weight of water `= 18 g mol^(-1)` Molecular weight of ethanol `= 46 g mol^(-1)` In answering the following questions, consider the solutions to be ideal dilute solutions and solutes to be non-volatile and non-dissociative. Water is added to the solution M such that the mole fraction of water in the solution becomes 0.9. The boiling point of this solution isA. 380.4 KB. 376.2 KC. 375.5 KD. 354.7 K |
Answer» Correct Answer - B `{:("Solute ethanol","Solvent " H_(2)O),(0.1,0.9),(4.6 gm,16.2 gm):}` `Delta T_(b)=0.52((4.6xx1000)/(46xx16.2))` `Delta T_(b)=3.20` `T_(b)=3.20+373=376.20 K` |
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