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What is distillation? How does it basically work?
Purification of liquid (liq) with low boiling point (bp).
Heat solution (sol).
Vapours rise to heat up the thermometer and vapours go into condensor.
Condensor condenses the vapours to give a liquid.
Liquid runs down condensor and drips into collecting vessel.
What does contamination of (solids) slds and liqs lead to?
Contamination leads to decreasing and broadening of mp of slds.
Contamination leads to increasing or decreasing of bp of liqs.
What are the three common types of distillation? Differentiate each.
Simple distillation: Separates liq from dissolved sld or two liqs that differ in bps > 100ºC.
Fractional distillation: Separates liqs differing in bps < 100ºC. Used for separating components in crude oil.
Steam distillation: Separating water insoluble compound using steam. Used for separating natural products.
Explain the principle of distillation.
When the liquid in the distillation flask boils, vapour rises to the top of the flask, through the distillation head, past the thermometer, out the side arm and into the condenser. Some vapour wil condense on the walls of the flask, three-way adapter, and on the thermometer.
As long as vapour is flowing out the side arm, the condensed liquid on the tip of the thermometer is in equilibrium with said vapour, and an accurate boiling point can be determined.
Generally, when thermal equilibrium has been reached, the boiling point remains relatively constant (not changing by more than 1-2°C) during the distillation. When a significant change in temperature (decrease or increase by 5°C) is observed, the vapour composition has changed and therefore it's likely that another compound wil come out of the tail adapter. When the temperature changes significantly, collect the distillate with another vessel since this component wil not be pure.
Explain how distillation is set up.
Raise hot plate.
Place df on hot plate, and clamp the df. Liquid must be half of the rb flask.
Insert three-way adapter.
Insert condenser into three way adapter. Use elastic to bind the three way adapter and the water out inlet.
Clamp the condenser. Don’t make it too tight or it will have contort the set up and allow vapours to escape.
Insert the take-off adapter. Use another elastic to bind the water out inlet and the take off adapter.
Insert the thermometer into three-way adapter. Tip of thermometer right below the intersection of three-way adapter. If the bulb is placed too high, no accurate reading. If too low, temp read may not be representative of what’s collected.
Place distillate flask below take-off adapter and in an ice bath,
Heat up. General distill rate would be 1 drop/second, controlled by heating temp.
How do you deconstruct the distillation setup?
In the reverse order of setting the distillation setup.
What are the two usual reasons as to why one would perform a distillation?
Removing hazardous compounds from solv or liq into the distillation flask (df) as a non-volatile sld or concentrated sol.
Purifying volatile liqs since the components distill according to bp.
What happens if you have a mixture of two or more liqs in regards to their boiling bps when heated up together?
What is an azeotrope?
Molecules will interact to change the bp of the mixture such that it will be different from the bp of either component.
Azeotrope: Liq mixture with constant bp. An azeotrope’s bp can be > or < the bp of its constituents.
What should you do when the temp of distillation head changes?
What should you take down over time to maintain purity?
When the temp of the distillation head changes, collect distillate w/ a different flask for purity.
Record bp (range of bps recorded) of droplets going into collection vessel.
What are the four NEVERS for a df?
Never distill df to dryness. Presence of liq prevents flask from overheating, breaking, and pyrolytic tars.
Never more than half in df.
Never too large df for vapour waste filling in flask.
Never too small df for distillation material loss due to foaming, splashing, or boiling up into the distillation head.
For a liq to boil, what does the temp need to be?
For a liq to boil, needs to be slightly above bp before initiation of bubble can begin.
If bubbles of vapours form within this liq, what are the two things that could happen?
Bubbles will collapse if its below a minimum size because of the surface tension of the liq.
Bubbles will grow to the surface of the liq.
If a liquid that is free of sld impurities or free of dissolved gases is heated slowly, what does the temp tend to be?
A temp well beyond bp of the liquid can be reached without any boiling taking place.
What is superheating?
What is bumping?
Increasing energy required for bubble formation.
Bubble forming with explosive power leading to splashing of solvent.
What are the two things that can be done to prevent overheating and bubbling?
(1) Continue to swirly the flask or vessel while it is being heated. However, most of the time we cannot swirl for extended periods of time, so (2) we add a boiling aid (an inert material, e.g. stir bar) to liq so that bubbles are formed easily.
What is the one NEVER for a boiling aid?
Never add it to a hot liq.
What does the IR spectrophotometer measure?
IR spectrophotometer will measure amount of light trasmitted through the sample.
What does attenuated total reflectance (ATR) only require?
What is the cause of a bad quality spectrum (spec) on this note? What does this look like on a spec?
Intimate contact of crushed analyte sample with crystal.
A bad quality IR spec is the result of sample not completely covering crystal surface. Bad quality IR spectra are characterized by a low signal to baseline ration and basically appearing hairy.
What is the one common fix with collecting IR spectra in regards to ATR coverage of crystal?
Ensure sample covers entire surfave of crystal and recollect spectrum.
What is the two most common problems with collecting IR spectra in regards to concentration (conc)?
If conc is large, then swamp detector of spectrophotometer.
If conc is small or dilute, then peaks will be lost in noise of detect
In regards to intensity of peaks, what will more functional groups bring about vs. less functional groups?
More functional groups in sample will absorb more and lead to higher intensity than other groups with less of their functional group.
