Answer Happy

3. Large sections of the description in this question are taken from the Wikipedia entry on Azeotropes. Azeotrope means 'to boil without changing'. A mixture is given this label when it is not possible to separate its components by fractional distillation. (a) Systems where both components can be completely separated by fractional dis- tillation are not azeotropes. The phase diagram of a non-ideal two component mixture is shown in Figure 2 i. Draw on the figure, starting in the liquid phase at a mole fraction of 0.5, a fractional distillation pathway that purifies the vapour. ii. As the vapour becomes purer, what happens to the remaining liquid? (1) In general, a positive azeotrope boils at a lower temperature than any other ratio of its constituents. Positive azeotropes are also called minimum boiling mixtures or pressure maximum azeotropes. A well-known example of a positive azeotrope is 95.63% ethanol and 4.37% water (by mass). Ethanol boils at 78.4C, water boils at 100C, but the azeotrope boils at 78.2C, which is lower than either of its constituents. An example of this type of behaviour is seen in Figure 3 Start with a liquid mixture at a 0.2 mole fraction of chloroform and show by using fractional
Liquid Pressure L+V Vapour 0 Mole Fraction A Figure 2: A phase diagram for a non-azeotrope mixture. distillation that it is not possible to separate completely the mixture since frac- tional distillation leads to the azeotrope mixture. Pressure Waxinum Azeotrope Mixture of Chloroform and Methanol Constant Temperature T-298.15K Azeotrope Liquid only Liquid composition Boiling point curve Preware Minimum Azeotrope Mixture of Water and Formic Acid 50 Constant Temperature 5T-298.15 K (25 "C) Pure boiling point of Formic Acid 54 52 5 43 Liquid composition Boiling point curve PrePA 82 MSM Liquid only Coexistent phases Pure boiling point of Chloroform Vapor only Vapor composition Dew point curve Pure boiling point of Water 32 Pure boling point of Methanol 20 20 Vapor corposition Dew point curve Azeotrope Vapor only 01 02 03 04 05 06 07 08 09 Hele fraction for Acid Fox 01 02 03 04 05 06 07 08 09 Fraction Conform Chardom Figure 3: A diagram of a positive Figure 4: A diagram of a negative azeotrope. azeotrope. (c) In general, a negative azeotrope boils at a higher temperature than any other ratio of its constituents. Negative azeotropes are also called maximum boiling mixtures or pressure minimum azeotropes. An example of a negative azeotrope