Lab 1: Distillation Flashcards
How is Distillation different than Refluxing?
In Distillation, the condensate is returned to a separate vessel called a receiver. In Refluxing, the condensate is returned to the original vessel.
What is the Distillation technique useful for?
1) Useful for separating a mixture when the components of the mixture have different boiling points
2) The principle method used for purifying a liquid.
What are the 3 conditions that must be followed in Distillation?
1) At least one component in the mixture must be volatile (ie. there could be nonvaolatile solids present which would be left behind in the distillation flask)
2) If two or more volatile liquids are to be separated, then they must have a wide separation between their boiling points (eg. 50 degrees Celsius.
3) The components must not form an azeotrope
If a liquid is pure, will the b.p. measured remain constant throughout distillation?
Yes.
If the liquid of a mixture of two or more miscible (ie. soluble in all proportions) substances, will the boiling point be constant? If not, explain why not.
No, the b.p. will not be constant and will vary continuously during distillation because the composition of the liquid being distilled also varies continuously during the distillation; since the vapour pressure of the liquid varies with its composition, so therefore will the boiling point.
What is a specific example of Azeotropes?
Ethanol and water will form an azeotropic mixture at 95% and 5% respectively).
Define Refractive Index. How does refraction happen?
The refractive index is the measure of the change in the light path (refraction) as light passes at an angle from one medium to another (ie. air to liquid). This is due to the difference in light velocity in the two media. The extent to which the beam is refracted depends on the relative concentration of atoms and on the arrangement within the molecule; Hence the refractive index is a unique property of each medium.
Why is Refractive Index important? What is it dependent on?
The Refractive Index is the criteria for a pure liquid. It is a physical constant that is dependent on the wavelength of light and the temperature, and for most purposes, these are standardized to the sodium D line (wavelength = 598 nm) and 20 degrees Celsius. Because the refraction of light is an additive property it can be used to determine the concentration of solutions, to identify copounds and to determine their purity.
What is the device the takes refractive index readings?
Refractometer.
How do we set up and minimize the strain placed on the all-glass system distillation apparatus?
1) Clamp the RB flask to the vertical support.
2) Place the stillhead adapter with thermometer on top of the RB flask
3) Secure the takeoff adapter to the condenser by means of an elastic band. Lubricate the rubber tubings with water; then attach them securely to the condenser
4) Join the condenser to the stillhead adapter and secure it by clamping the center of the condenser to the horizonal bar, using a three-prong clamp (for less stress, the two prongs should be on the bottom)
5) Position the receiver beneath the take-off adapter
6) Put both rubber tubings over the horizontal bar. Connect the lower tubing on the condenser to the water tap and lower the other one into the sink. Turn on the water slowly and check to the flow rate. (In a condenser, the direction of the flow of water is always against gravity).
7) Connect the heating mantle to the rheostat. Position the mantle snugly under the RB flask, using the large ring clampand wooden square. Plug the rheostat into the wall socket.
How is smooth boiling achieved?
By placing a boiling chip into the solution prior to heating. These tiny chips are very porous rocks, which release bubbles of entrapped air to the solution being heated. These bubbles provide a path by which the vapour of the boiling liquid can be smoothly led to the surface and released.
Is an initial high heat input necessary to bring the solution to the boiling point?
Yes, the rheostat is usually set to a maximum, then once boiling begins, the heat input is reduced to maintain a dropping rate of the condensate into the receiver one drop per second.
How can we tell if the liquid and vapour are at equilibrium?
There should always be a droplet of condensate on the thermometer tip, and as it falls back into the boiling flask another droplet should form from the surroung vapours. Rheostat needs to be adjusted to maintain this tate
Should the system operate as adiabatically as possible? How do we minimize large heat loss?
Yes. To minimize large heat loss, insulate the distilling flask and stillhead adapter (and fracitoning column, if being used) with aluminum foil. This is especially important for fractional distillation.
Why and How do we calibrate a thermometer?
For accurate temperature readings, a thermometer that has not been used before must always be calibrated. We accomplish this by placing it into a beaker with ice cold water, ensuring the immersion line is covered by the liquid. Check the temperature after a few minutes.
