chem_lab_outlines-1

chem_lab_outlines-1 - Chem Lab Outlines Experiment 1 Simple...

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Chem Lab Outlines Experiment 1 – Simple Distillation - distillation – usual method for separation and purification of liquids - vapor pressure – the pressure exerted by the vapor in equilibrium with the liquid - boiling point – the temperature at which the vapor pressure of a liquid equals some external pressure - normal boiling point – the temperature at which the vapor pressure of a liquid equals atmospheric pressure – 760 torr - volatile – any substance with appreciable vapor pressure in a temperature range under consideration - relationship between vapor pressure and absolute temperature o vapor pressure increases with temperature expontentially o differential equation dP/dT = P (enthalpy change) / RT^2 - Vapor pressure of a component in a solution o A volatile liquid with an insoluble involatile substance as a VP equal to volatile liquid pure o A volatile liquid with a soluble involatile substance has reduced VP due to dilution o Two volatile substances follow Raoult’s Law The partial pressure of A is equal to the pressure of pure A at that temperature times the mole fraction of A in solution The vapor is richer in the more volatile substance than the solution Bp changes as solution is distilled since composition of liquid changes Questions 1. The boiling point is the temperature at which the vapor pressure of a liquid equals some external pressure. The normal boiling point is the temperature at which the vapor pressure of a liquid equals atmospheric pressure of 760 torr 2. a. dP/dT= P (change in enthalpy)/RT^2 As temperature and pressure increase, the molecules in the liquid have a greater collective kinetic energy. This slight increase in average kinetic energy reduces the amount of energy needed to release the liquid into vapor. Higher temperature brings the liquid state closer in character to the final vapor state reducing the energy gap between them b. the liquid’s critical temperature is the temperature above which the substance can exist only as a gas. The liquid’s critical pressure is the pressure below which the substance can exist only as a gas c. Carbon dioxide can only exist as a gas above 31 degrees celcius regardless of pressure. If the room is above 31, the shaking of liquid CO2 can’t be heard since all contents have been vaporized. 3. a. dP/dT = P (change in entropy)/RT a lower Tbp of one organic solvent at a given pressure will result in a steeper slope than an organic solvent with a higher Tbp b. v
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c. v i. H-bonding and dipole-dipole moments result in stronger intermolecular bonding in the liquid state and consequently require more energy to vaporize ii. Because H-bonding requires specific orientation, the liquid
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chem_lab_outlines-1 - Chem Lab Outlines Experiment 1 Simple...

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