16.1 Flashcards
Basic set if Quickfit apparatus includes…
Round-bottom or pear-shaped flask Receiver Screw-tap adaptor Condenser Still head
(Check book page 240 for pictures)
Reflux meaning
Continual boiling and condensing of reaction mixture back to original container to ensure reaction takes place without the contents of the flask boiling dry
Why reflux used as common procedure?
Many organic reactions slow at room temp, so common for reactions to be heated to overcome activation energy and increase rate of reaction
Equipment needed for reflux
Round-bottom/pear-shaped flask Condenser Rubber tubing Stand and clamp Heat source (bunsen burner with tripod and gauze, or heating mantle)(water bath if reaction carried out under 100C)
Flaming mantle safer with flammable liquids as no fire
When refluxing, what do you need to add to the flask?
Anti-bumping granules and reaction mixture
Why are anti-bumping granules added during reflux?
So that contents will boil smoothly. If granules not used, large bubbles form at bottom of liquid, make glassware vibrate/jump violently
For reflux, what dies setup look like?
Stand holding flask. Flask clamped by NECK. Condenser placed into flask in upright position.
Precautions to take when clamping a condenser during reflux?
Clamp loosely as glass very fragile and can easily break. Never put a stopper at top of condenser, as pressure could build up, make it explode.
Which side of the condenser does water enter through during reflux?
Enters at bottom and leaves at the top, to ensure outer jacket is full
Why is reflux a good method?
Allows liquid be continually boiled whilst reaction happens. Prevents volatile components escaping and flask from boiling dry. Vapour rises up condenser, meets outer jacket containing cold water, condenses, drips back into flask
Once reflux complete, why might you want to use distillation?
Crude liquid or solid product present in flask needs be purified to remove any by-products or remaining reactants. Distillation allows us separate pure liquid from impurities
Equipment needed for distillation
Round-bottom / pear-shaped flask Condenser Rubber tubing Heat source Stand and clamp Screw-cap adaptor Receiver adaptor Still head Thermometer
What does setup look like for distillation?
Flask clamped by neck, then still head ADAPTOR connected to flask.
Still head/thermometer pocket put into top of still head adaptor.
Receiver adaptor clamped (on separate stand) at point where connected to condenser - means no clamp needed for condenser.
Rubber tubing needed for condenser, water enters through lowest point (for distillation, this is closest point to receiver adaptor)
Flask underneath receiver adaptor to collect distillate
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Once apparatus set up, flask heated, mixture in flask start boil, different liquids in mixture have different boiling points, so lower boiling point liquid will boil first (more volatile). Vapour leaves flask, moves ro other parts of apparatus. Leave behind less volatile. When vapour reaches condenser, condenses, drips into collecting flask
What does it mean if tou get 2 layers in collecting flask?
When prepare sample of organic liquids, water may be obtained along with product. If this happened, 2 liquid layers inside collection flask, one organic, one aqueous/water layer. To tall which is which, add water - layer that grows in size is aqueous.
How to separate if 2 layers in collecting flask?
Use a separating funnel:
1) ensure tap of separating funnel is closed
2) pour mixture of liquids into separating funnel, place stopper at end, invert to mix contents
3) allow layers to settle
4) add some water to see which layer increases in volume - this is aqueous layer
5) place conical flask under separating funnel, remove stopper, open tap until whole of lower layer has left funnel
6) place second flask under separating funnel to collect other layer
7) now have 1 conical flask with organic, one with aqueous (label flasks)
