- a way to purify liquids (separated based on boiling points)
Reason for carrying out (distillation)
wrap with tin foil to minimize heat loss
Insulation of apparatus (distillation)
to ensure vapor condenses in sidearm
Wrapping with a wet paper towel - why? (distillation)
below the sidearm, not touching glass of apparatus
Position of the thermometer (distillation)
inside beaker but not touching the sides of beaker
Position of end of sidearm (distillation)
scrape sand away from the round bottom flask and/or lower sand bath temp
How to control heat (distillation)
- acending vapors and decending liquids wont reach equilibrium
- overheating can cause bumping in the flask
- need proper temperature gradient to ensure separation of liquids.
What may occur if the distillation occurs too quickly - why (distillation)
- solution will never boil
- liquids and vapors will not reach equilibrium
- liquids wont separate
- vapors wont condense
-temperature can drop too low
What may occur if the distillation occurs too slowly why (distillation)
can change mole fractions and temperature values of distillation
Effect of changing atmospheric pressure on boiling point (distillation)
simple: mixtures of liquids with bp differences over 75C
fractional: mixtures of liquids with bp differences under 75C
Uses of simple and fractional distillation - what kinds of mixtures are suitable for each kind of distillation
requirements
- significant contact between liquid and vapor pahses in the columns: achieved by filling column with packing material with large surface are
- maintenance of proper temperature gradient along the column
problems:
- flooded column - solve by
Requirements for a successful fractional distillation -including problems and how to solve
should rise at a fairly constant rate
Behavior of temperature during a simple or fractional distillation of a mixture.
mixture of liquids of a certain definite composition that distills at a constant temperature without change in composition. boils above or below both liquids bps. non azeotrope boils in between both liquids boiling points
minimum: boils lower than either
Definition of azeotrope (minimum and maximum) (distillation)
unrecoverable distillate that wets the column packing
Definition of hold up (distillation)
- packing material used to increase the surface area
- should not be too dense that pressure changes take place within the column
- too much will cause too large of a surface area and cause the distillate to hold up in column
Use of a packing material and criteria for choosing, why should the packing material not be too dense or have too large a surface area (distillation)
when substances have too high of boiling points or are sensitive to oxidation use vacuum. Accomplishes distillation at a reduced pressure. used with immiscible liquids
Purpose of vacuum distillation
compounds that have too high of boiling points or are sensitive to oxidation
What kind of compounds need to be purified by vacuum distillation
- used for compounds that are not very volatile
- water is used to mix with non volatile substances to entrain then
- Difference: steam uses non volatile substances, vacuum uses substances with low boiling points and sensitive to oxidation
Steam distillation - uses, what kind of mixture used in steam distillation - difference between vacuum distillation and steam distillation
- there needs to be adequate amounts of water and the organic component present to saturate the vapor space
Precautions
- never distill to dryness as dry residue of liquids can be explosive (dont fill more than 2/3 full)
- never distill in closed system o
What requirement is necessary for boiling point in steam distillation to be constant? Precautions about distilling to dryness, distilling in closed system.
- loose connectors
- temperature variations (due to environment and not constant heating)
- large surface area of microscale apparatus
- thermometer calibration
- positioning of sidearm
- holdup in fractional distillation
- significant amount of distillat
Sources of error in a distillation - what happens and why it happens
- positioning of sidearm
- holdup in fractional distillation
- significant amount of distillate left adhering to glass
- loose connectiors
Reasons for not recovering all liquid in distillation and why
a) (570)(.68) = 387.6, (810)(.32) = 259.2, XB = .40
b) .52 = x/748, x = 388.96, 388.96 = (590)(x), x = (.66)(100) = 66%
- Calculate the mole fraction of B (XB) in the vapor if a mixture of liquids is 68%A and 32%B. The vapor pressure of pure A (PA�) is 570 torr and the vapor pressure of pure B (PB�) is 810 torr. Show calculations and give answer to 2 decimal places.
- The
condensing of higher boiling vapor releases heat which causes the vaporization of the lower boiling pt liquid
What specifically causes the vaporization of the lower boiling liquid on the packing in a fractional distillation?
equilibrium is attained between the ascending vapor and descending liquid when a number of distillations take place in a fractional column. there is no heat gained or heat lost with the surroundings
Explain the adiabatic process as it specifically pertains to a fractional distillaion.
made by analyzing the proportion of lower to higher boiling material at the top of the column and in the distillation pot
How is the calculation for HETP of a column made?
boiling stones dont activate in a vacuumed system which prevents them from absorbing or trapping liquids to control bumping
Why would boiling stones not be able to control the bumping of liquids in vacuum distillation?
you must heat the flask only after the system is vacuumed to the desired pressure
In vacuum distillation, how you do ensure that the liquid does not boil too suddenly upon reduction of pressure?
it can depress the boiling point of the substances to prevent decomposition
What aspect of water makes it favorable to use in steam distillation?