Liquid Separations Flashcards
(48 cards)
raoult’s law
States that the partial pressure of a liquid above a solution is equal to the vapour pressure of the pure solvent at the same temperature
what is vapour pessure?
It is the pressure exerted by vapour molecules on the liquid surface when a liquid is in a container.
what happens when a liquid in a closed vessel reaches dynamic equilibrium?
The rates at which the liquid turns to vapour and vapour condenses back to liquid become equal, resulting in saturated vapour pressure (SVP).
how does SVP vary with temperature?
SVP increases with temperature because more molecules acquire energy to escape into vapour
how does SVP vary with temperature?
SVP increases with temperature because more molecules acquire energy to escape into vapour
What is the difference between miscible d immiscible liquids?
Miscible liquids form a homogeneous solution in any proportion (e.g., H₂O and CH₃OH), while immiscible liquids separate into distinct layers (e.g., H₂O and paraffin oil).
define an ideal solution
An ideal solution is where the forces of attraction between different molecules in the mixture are of the same strength as in the pure liquids, with no volume change on mixing.
how do you calculate total vapor pressure in a mixture?
Add the partial pressures of each liquid in the mixture.
how do you calculate total vapor pressure in a mixture?
Add the partial pressures of each liquid in the mixture.
what is fractional distillation?
It is a process to separate liquid mixtures based on differences in boiling points.
what happens as vapour rises in a fractionating column?
It becomes richer in the more volatile component, eventually producing pure vapour at the top.
what happens as vapour rises in a fractionating column?
It becomes richer in the more volatile component, eventually producing pure vapour at the top.
how does packing improve the efficiency of fractional distillation?
Packing provides a surface area for condensation and ensures equal rates of vapour rise and liquid descent.
what causes negative deviation from Raoult’s law?
Stronger forces of attraction in the mixture than in the pure liquids, leading to lower SVP and higher boiling points.
what happens to volume and heat in mixtures showing negative deviation?
The volume contracts, and heat is released (ΔH is negative).
what happens to volume and heat in mixtures showing negative deviation?
The volume contracts, and heat is released (ΔH is negative).
what is an azeotrope?
A constant boiling point mixture that retains the same composition in liquid and vapour phases during boiling.
provide an example of azeotropic behaviour
H₂O and HNO₃ mixtures form an azeotrope at 121°C with 31.8% H₂O and 68.2% HNO₃.
what is the positive deviation from Raoults Law?
A pair of liquids will mix and form a mixture, which shows a positive deviation from Raoult’s Law when there are weaker forces in the mixture than in the pure liquids.
When these liquids mix, there will be:
i. an increase in volume
ii. an absorption of heat
what are immiscible liquids?
A pair of liquids is said to be immiscible if they separate into distinct layers on mixing, with the less dense liquids above.
properties of immiscible liquids
Whenever a pair of immiscible liquids is in a container, each liquid exerts its total SVP above the mixture.
The mixture has to be agitated by either shaking or stirring for the lower liquid to establish its SVP.
Does boiling point vary with composition for immiscible liquids?
no because each liquid exerts its total SVP above the mixtures so all the mixtures will have the same boiling point
what is the rule of boiling point with immiscible liquids?
The boiling point of a pair of immiscible liquids is always lower than the boiling point of either liquid.
what is stam distillation?
Steam distillation is a method of purification and extraction of compounds which tend to decompose at temperature values less than their boiling points.
