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CHEM 2422 Distillation (Lab 3)
Terms in this set (22)
What are the benefits of carrying out distillation under reduced pressure?
Reduction in pressure causes a reduction in boiling point, meaning boiling occurs faster. This is useful for distilling liquids with high boiling points.
Why is it necessary to add boiling stones during distillation?
Boiling stones prevent bumping due to super heating.
The pressure created by vapor molecules striking the walls of the container they occupy.
The temperature of a liquid at which the vapor pressure of the liquid becomes equal to the atmospheric pressure.
Why does the vapor pressure of a liquid increase with temperature?
The vapor pressure of a liquid increases with temperature. This is because as temperature increases, molecules escape from the vapor until equilibrium is reestablished.
Be able to...
-Estimate volume of a boiling liquid with and without a column using distillation curves (lab report)
-Identify mole fraction for vapor line
Why is fractional distillation more effective at separating the mixture into its components?
Fractional distillation better separates components because the iron wool in the column causes the liquid to re-condense, thus preventing the less volatile liquid from evaporating.
Why does a pure liquid have a constant boiling point, but a liquid with a constant boiling point is not necessarily pure?
In some mixtures, the vapor has the same portion of constituents as the unboiled mixture. Azeotropes are mixtures of compounds with the same boiling point, thus the boiling point is fixed.
What effect does a reduction of atmospheric pressure have on the boiling point of a liquid?
When pressure is reduced, boiling point is also reduced. Boiling point can differ by location depending on pressure.
Why doesn't a pure liquid in a distilling flask vaporize all at once when the boiling temperature is reached?
Additional heat must be supplied for a phase change to occur.
Why is it dangerous to heat a liquid in a distilling apparatus that is closed tightly at every joint and has no vent to the atmosphere?
The increase in heat and pressure inside the apparatus will increase and possibly explode the distillation equipment.
Why is it important that the cooling water in a distillation apparatus enter the condenser jacket at the lower end and exit at the upper end?
It ensures efficient condensing. The coolest water is the last water to surround the condenser, it is able to remove any residual heat.
Why should a distilling flask be filled no more than two thirds of its capacity at the beginning of the distillation procedure?
If the flask is to full, it could boil over without vaporizing contaminate the pure distillate.
Dalton's Law of Partial Pressures
Total pressure of a gas is equal to the sum of the partial pressure of the component gases
What is the purpose of distillation?
To purify liquids, separation is based on boiling point
Is performed when trace impurities need to be removed from a relatively pure compound, or when a mixture of compounds with significantly different boiling points need to be separated.
Is used when the difference in boiling points of the components in the liquid mixture is not large. Column is packed with an appropriate material; packing of column results in liquid mixture being subjected to many vaporization -condensation cycles it moves up the column. Composition of the vapor gradually becomes enriched in the lower boiling component. Near top of column, nearly pure vapor reaches condenser and condenses back to liquid.
Different vapor and liquid lines due to interactions between the compounds. Two or more liquids whose proportions cannot be altered by simple distillation, because when an azeotrope is boiled, the vapour has the same proportions of constituents as the unboiled mixture.
How do impurities affect boiling point?
Impurities raise boiling point.
This set is often in folders with...
CHEM 2242 Extraction (Lab 4)
CHEM 2242 Recrystallization (Lab 2)
CHEM 2242 Melting Point (Lab 1)
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